number
A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers c ...
natural number
In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country").
Numbers used for counting are called ''cardinal ...
semiprime
In mathematics, a semiprime is a natural number that is the product of exactly two prime numbers. The two primes in the product may equal each other, so the semiprimes include the squares of prime numbers.
Because there are infinitely many prime ...
and
composite number
A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself. Every positive integer is composite, prime, ...
composite number
A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself. Every positive integer is composite, prime, ...
, its proper
divisor
In mathematics, a divisor of an integer n, also called a factor of n, is an integer m that may be multiplied by some integer to produce n. In this case, one also says that n is a multiple of m. An integer n is divisible or evenly divisible by ...
s being and . Four is the sum and product of
two
2 (two) is a number, numeral and digit. It is the natural number following 1 and preceding 3. It is the smallest and only even prime number. Because it forms the basis of a duality, it has religious and spiritual significance in many cultur ...
with itself: + = = x , the only number such that + = = x , which also makes four the smallest squared
prime number
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
. In
Knuth's up-arrow notation
In mathematics, Knuth's up-arrow notation is a method of notation for very large integers, introduced by Donald Knuth in 1976.
In his 1947 paper, R. L. Goodstein introduced the specific sequence of operations that are now called ''hyperoperati ...
, , and so forth, for any number of up arrows. By consequence, four is the only square one more than a prime number, specifically
three
3 is a number, numeral, and glyph.
3, three, or III may also refer to:
* AD 3, the third year of the AD era
* 3 BC, the third year before the AD era
* March, the third month
Books
* '' Three of Them'' (Russian: ', literally, "three"), a 1901 ...
. The sum of the first four prime numbers
two
2 (two) is a number, numeral and digit. It is the natural number following 1 and preceding 3. It is the smallest and only even prime number. Because it forms the basis of a duality, it has religious and spiritual significance in many cultur ...
+
three
3 is a number, numeral, and glyph.
3, three, or III may also refer to:
* AD 3, the third year of the AD era
* 3 BC, the third year before the AD era
* March, the third month
Books
* '' Three of Them'' (Russian: ', literally, "three"), a 1901 ...
+
five
5 is a number, numeral, and glyph.
5, five or number 5 may also refer to:
* AD 5, the fifth year of the AD era
* 5 BC, the fifth year before the AD era
Literature
* ''5'' (visual novel), a 2008 visual novel by Ram
* ''5'' (comics), an awa ...
+
seven
7 is a number, numeral, and glyph.
7 or seven may also refer to:
* AD 7, the seventh year of the AD era
* 7 BC, the seventh year before the AD era
* The month of
July
Music Artists
* Seven (Swiss singer) (born 1978), a Swiss recording artist ...
is the only sum of four consecutive prime numbers that yields an
odd
Odd means unpaired, occasional, strange or unusual, or a person who is viewed as eccentric.
Odd may also refer to:
Acronym
* ODD (Text Encoding Initiative) ("One Document Does it all"), an abstracted literate-programming format for describing X ...
three
3 is a number, numeral, and glyph.
3, three, or III may also refer to:
* AD 3, the third year of the AD era
* 3 BC, the third year before the AD era
* March, the third month
Books
* '' Three of Them'' (Russian: ', literally, "three"), a 1901 ...
and
five
5 is a number, numeral, and glyph.
5, five or number 5 may also refer to:
* AD 5, the fifth year of the AD era
* 5 BC, the fifth year before the AD era
Literature
* ''5'' (visual novel), a 2008 visual novel by Ram
* ''5'' (comics), an awa ...
, which are the first two
Fermat prime
In mathematics, a Fermat number, named after Pierre de Fermat, who first studied them, is a positive integer of the form
:F_ = 2^ + 1,
where ''n'' is a non-negative integer. The first few Fermat numbers are:
: 3, 5, 17, 257, 65537, 429496 ...
s, like seventeen, which is the third. On the other hand, the
square
In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90- degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length a ...
of four 42, equivalently the
fourth power
In arithmetic and algebra, the fourth power of a number ''n'' is the result of multiplying four instances of ''n'' together. So:
:''n''4 = ''n'' × ''n'' × ''n'' × ''n''
Fourth powers are also formed by multiplying a number by its cube. Further ...
of two 24, is sixteen; the only number that has = as a form of
factorization
In mathematics, factorization (or factorisation, see English spelling differences) or factoring consists of writing a number or another mathematical object as a product of several ''factors'', usually smaller or simpler objects of the same kind ...
division
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
*Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
(÷); and four basic
number system
A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can ...
s, the
real number
In mathematics, a real number is a number that can be used to measure a ''continuous'' one-dimensional quantity such as a distance, duration or temperature. Here, ''continuous'' means that values can have arbitrarily small variations. Every ...
s ,
rational number
In mathematics, a rational number is a number that can be expressed as the quotient or fraction of two integers, a numerator and a non-zero denominator . For example, is a rational number, as is every integer (e.g. ). The set of all rat ...
s ,
integer
An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...
s , and
natural number
In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country").
Numbers used for counting are called ''cardinal ...
s .
Each natural number divisible by 4 is a difference of squares of two natural numbers, i.e. = − . A number is a multiple of 4 if its last two digits are a multiple of 4. For example, 1092 is a multiple of 4 because .
Lagrange's four-square theorem
Lagrange's four-square theorem, also known as Bachet's conjecture, states that every natural number can be represented as the sum of four integer squares. That is, the squares form an additive basis of order four.
p = a_0^2 + a_1^2 + a_2^2 + a_ ...
states that every positive integer can be written as the sum of at most four
square number
In mathematics, a square number or perfect square is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, 9 is a square number, since it equals and can be written as .
The usu ...
s. Three are not always sufficient; for instance cannot be written as the sum of three squares.
There are four
all-Harshad number
In mathematics, a harshad number (or Niven number) in a given number base is an integer that is divisible by the sum of its digits when written in that base.
Harshad numbers in base are also known as -harshad (or -Niven) numbers.
Harshad number ...
s: 1, 2, ''4'', and 6. 12, which is divisible by four thrice over, is a Harshad number in all bases except
octal
The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. This is to say that 10octal represents eight and 100octal represents sixty-four. However, English, like most languages, uses a base-10 number ...
.
A four-sided plane figure is a
quadrilateral
In geometry a quadrilateral is a four-sided polygon, having four edges (sides) and four corners (vertices). The word is derived from the Latin words ''quadri'', a variant of four, and ''latus'', meaning "side". It is also called a tetragon, ...
or quadrangle, sometimes also called a ''tetragon''. It can be further classified as a rectangle or ''oblong'',
kite
A kite is a tethered heavier-than-air or lighter-than-air craft with wing surfaces that react against the air to create lift and drag forces. A kite consists of wings, tethers and anchors. Kites often have a bridle and tail to guide the fac ...
,
rhombus
In plane Euclidean geometry, a rhombus (plural rhombi or rhombuses) is a quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The ...
, and
square
In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90- degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length a ...
.
Four is the highest degree general
polynomial equation
In mathematics, an algebraic equation or polynomial equation is an equation of the form
:P = 0
where ''P'' is a polynomial with coefficients in some field (mathematics), field, often the field of the rational numbers. For many authors, the term '' ...
four-color theorem
In mathematics, the four color theorem, or the four color map theorem, states that no more than four colors are required to color the regions of any map so that no two adjacent regions have the same color. ''Adjacent'' means that two regions sha ...
states that a planar graph (or, equivalently, a flat
map
A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.
Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...
of two-dimensional regions such as countries) can be colored using four colors, so that adjacent vertices (or regions) are always different colors. Three colors are not, in general, sufficient to guarantee this. The largest planar
complete graph
In the mathematical field of graph theory, a complete graph is a simple undirected graph in which every pair of distinct vertices is connected by a unique edge. A complete digraph is a directed graph in which every pair of distinct vertices is ...
has four vertices.
A solid figure with four faces as well as four vertices is a
tetrahedron
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all th ...
, which is the smallest possible number of faces and vertices a
polyhedron
In geometry, a polyhedron (plural polyhedra or polyhedrons; ) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices.
A convex polyhedron is the convex hull of finitely many points, not all on ...
can have. The regular tetrahedron, also called a 3- simplex, is the simplest
Platonic solid
In geometry, a Platonic solid is a convex, regular polyhedron in three-dimensional Euclidean space. Being a regular polyhedron means that the faces are congruent (identical in shape and size) regular polygons (all angles congruent and all e ...
. It has four
regular triangle
In geometry, an equilateral triangle is a triangle in which all three sides have the same length. In the familiar Euclidean geometry, an equilateral triangle is also equiangular; that is, all three internal angles are also congruent to each ...
s as faces that are themselves at dual positions with the vertices of another tetrahedron. Tetrahedra can be inscribed inside all other four Platonic solids, and tessellate space alongside the
regular octahedron
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
in the
alternated cubic honeycomb
The tetrahedral-octahedral honeycomb, alternated cubic honeycomb is a quasiregular space-filling tessellation (or honeycomb) in Euclidean 3-space. It is composed of alternating regular octahedra and tetrahedra in a ratio of 1:2.
Other names incl ...
convex
Convex or convexity may refer to:
Science and technology
* Convex lens, in optics
Mathematics
* Convex set, containing the whole line segment that joins points
** Convex polygon, a polygon which encloses a convex set of points
** Convex polytop ...
figures:
*Two-dimensional: infinitely many
regular polygon
In Euclidean geometry, a regular polygon is a polygon that is direct equiangular (all angles are equal in measure) and equilateral (all sides have the same length). Regular polygons may be either convex, star or skew. In the limit, a sequence ...
s.
*Three-dimensional: five
regular polyhedra
A regular polyhedron is a polyhedron whose symmetry group acts transitively on its flags. A regular polyhedron is highly symmetrical, being all of edge-transitive, vertex-transitive and face-transitive. In classical contexts, many different equival ...
; the five
Platonic solid
In geometry, a Platonic solid is a convex, regular polyhedron in three-dimensional Euclidean space. Being a regular polyhedron means that the faces are congruent (identical in shape and size) regular polygons (all angles congruent and all e ...
s which are the
tetrahedron
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all th ...
octahedron
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
,
dodecahedron
In geometry, a dodecahedron (Greek , from ''dōdeka'' "twelve" + ''hédra'' "base", "seat" or "face") or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagon ...
regular polychora
In mathematics, a regular 4-polytope is a regular four-dimensional polytope. They are the four-dimensional analogues of the regular polyhedra in three dimensions and the regular polygons in two dimensions.
There are six convex and ten star regu ...
; the
5-cell
In geometry, the 5-cell is the convex 4-polytope with Schläfli symbol . It is a 5-vertex four-dimensional object bounded by five tetrahedral cells. It is also known as a C5, pentachoron, pentatope, pentahedroid, or tetrahedral pyramid. It i ...
, 8-cell or
tesseract
In geometry, a tesseract is the four-dimensional analogue of the cube; the tesseract is to the cube as the cube is to the square. Just as the surface of the cube consists of six square faces, the hypersurface of the tesseract consists of e ...
,
16-cell
In geometry, the 16-cell is the regular convex 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is one of the six regular convex 4-polytopes first described by the Swiss mathematician Ludwig Schläfli in the ...
,
24-cell
In geometry, the 24-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is also called C24, or the icositetrachoron, octaplex (short for "octahedral complex"), icosatetrahedroid, o ...
,
120-cell
In geometry, the 120-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is also called a C120, dodecaplex (short for "dodecahedral complex"), hyperdodecahedron, polydodecahedron, hec ...
, and
600-cell
In geometry, the 600-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is also known as the C600, hexacosichoron and hexacosihedroid. It is also called a tetraplex (abbreviated from ...
. The
24-cell
In geometry, the 24-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is also called C24, or the icositetrachoron, octaplex (short for "octahedral complex"), icosatetrahedroid, o ...
, made of regular
octahedra
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...
, has no analogue in any other dimension; it is self-dual, with its
24-cell honeycomb
In Four-dimensional space, four-dimensional Euclidean geometry, the 24-cell honeycomb, or icositetrachoric honeycomb is a regular polytope, regular space-filling tessellation (or honeycomb (geometry), honeycomb) of 4-dimensional Euclidean space by ...
dual to the
16-cell honeycomb
In four-dimensional Euclidean geometry, the 16-cell honeycomb is one of the three regular space-filling tessellations (or honeycombs), represented by Schläfli symbol , and constructed by a 4-dimensional packing of 16-cell facets, three around ...
.
*Five-dimensional and every higher dimension: three regular convex -
polytope
In elementary geometry, a polytope is a geometric object with flat sides ('' faces''). Polytopes are the generalization of three-dimensional polyhedra to any number of dimensions. Polytopes may exist in any general number of dimensions as an ...
icosahedra
In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons".
There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
and
dodecahedra
In geometry, a dodecahedron (Greek , from ''dōdeka'' "twelve" + ''hédra'' "base", "seat" or "face") or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagon ...
.
*Five-dimensional and every higher dimension: zero regular star-polytopes;
uniform
A uniform is a variety of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, ...
star polytopes in dimensions > are the most symmetric, which mainly originate from stellations of regular -polytopes.
Altogether, sixteen (or 16 = 42) regular convex and star polychora are generated from symmetries of ''four'' (4)
Coxeter
Harold Scott MacDonald "Donald" Coxeter, (9 February 1907 – 31 March 2003) was a British and later also Canadian geometer. He is regarded as one of the greatest geometers of the 20th century.
Biography
Coxeter was born in Kensington to ...
Weyl group
In mathematics, in particular the theory of Lie algebras, the Weyl group (named after Hermann Weyl) of a root system Φ is a subgroup of the isometry group of that root system. Specifically, it is the subgroup which is generated by reflections ...
s and
point groups
In geometry, a point group is a mathematical group of symmetry operations ( isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every ...
in the fourth dimension: the simplex, hypercube, icositetrachoric, and hexacosichoric groups; with the
demihypercube
In geometry, demihypercubes (also called ''n-demicubes'', ''n-hemicubes'', and ''half measure polytopes'') are a class of ''n''- polytopes constructed from alternation of an ''n''- hypercube, labeled as ''hγn'' for being ''half'' of the hy ...
group generating two alternative constructions.
There are also sixty-four (or 64 = 43) four-dimensional
Bravais lattice
In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by
: \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...
s, ''and'' sixty-four uniform polychora in the fourth dimension based on the same , , and
Coxeter groups
In mathematics, a Coxeter group, named after Harold Scott MacDonald Coxeter, H. S. M. Coxeter, is an group (mathematics), abstract group that admits a group presentation, formal description in terms of Reflection (mathematics), reflections (or Kal ...
uniform polyhedra
In geometry, a uniform polyhedron has regular polygons as faces and is vertex-transitive (i.e., there is an isometry mapping any vertex onto any other). It follows that all vertices are congruent.
Uniform polyhedra may be regular (if also ...
grand antiprism
In geometry, the grand antiprism or pentagonal double antiprismoid is a uniform 4-polytope (4-dimensional uniform polytope) bounded by 320 cells: 20 pentagonal antiprisms, and 300 tetrahedra. It is an anomalous, non-Wythoffian uniform 4-polytope ...
. There are also two infinite families of
duoprism
In geometry of 4 dimensions or higher, a double prism or duoprism is a polytope resulting from the Cartesian product of two polytopes, each of two dimensions or higher. The Cartesian product of an -polytope and an -polytope is an -polytope, wher ...
differential manifold
In mathematics, a differentiable manifold (also differential manifold) is a type of manifold that is locally similar enough to a vector space to allow one to apply calculus. Any manifold can be described by a collection of charts (atlas). One ma ...
s have some unique properties. There is only one
differential structure In mathematics, an ''n''-dimensional differential structure (or differentiable structure) on a set ''M'' makes ''M'' into an ''n''-dimensional differential manifold, which is a topological manifold with some additional structure that allows for dif ...
on except when = , in which case there are uncountably many.
The smallest non-
cyclic group
In group theory, a branch of abstract algebra in pure mathematics, a cyclic group or monogenous group is a group, denoted C''n'', that is generated by a single element. That is, it is a set of invertible elements with a single associative bina ...
has four elements; it is the
Klein four-group
In mathematics, the Klein four-group is a group with four elements, in which each element is self-inverse (composing it with itself produces the identity)
and in which composing any two of the three non-identity elements produces the third one. ...
. ''A''
alternating group
In mathematics, an alternating group is the group of even permutations of a finite set. The alternating group on a set of elements is called the alternating group of degree , or the alternating group on letters and denoted by or
Basic pr ...
s are not
simple
Simple or SIMPLE may refer to:
*Simplicity, the state or quality of being simple
Arts and entertainment
* ''Simple'' (album), by Andy Yorke, 2008, and its title track
* "Simple" (Florida Georgia Line song), 2018
* "Simple", a song by Johnn ...
complex numbers
In mathematics, a complex number is an element of a number system that extends the real numbers with a specific element denoted , called the imaginary unit and satisfying the equation i^= -1; every complex number can be expressed in the form ...
octonion
In mathematics, the octonions are a normed division algebra over the real numbers, a kind of hypercomplex number system. The octonions are usually represented by the capital letter O, using boldface or blackboard bold \mathbb O. Octonions hav ...
s . Under
Cayley–Dickson construction
In mathematics, the Cayley–Dickson construction, named after Arthur Cayley and Leonard Eugene Dickson, produces a sequence of algebras over the field of real numbers, each with twice the dimension of the previous one. The algebras produced b ...
s, the
sedenion
In abstract algebra, the sedenions form a 16-dimensional noncommutative and nonassociative algebra over the real numbers; they are obtained by applying the Cayley–Dickson construction to the octonions, and as such the octonions are isomorphic to ...
s constitute a further fourth extension over . The real numbers are ordered,
commutative
In mathematics, a binary operation is commutative if changing the order of the operands does not change the result. It is a fundamental property of many binary operations, and many mathematical proofs depend on it. Most familiar as the name of ...
algebras
In mathematics, an algebra over a field (often simply called an algebra) is a vector space equipped with a bilinear product. Thus, an algebra is an algebraic structure consisting of a set together with operations of multiplication and addition ...
, as well as
alternative algebra In abstract algebra, an alternative algebra is an algebra in which multiplication need not be associative, only alternative. That is, one must have
*x(xy) = (xx)y
*(yx)x = y(xx)
for all ''x'' and ''y'' in the algebra.
Every associative algebra is o ...
s with power-associativity. The complex numbers share all four multiplicative algebraic properties of the reals , without being ordered. The quaternions loose a further commutative algebraic property, while holding associative, alternative, and power-associative properties. The octonions are alternative and power-associative, while the sedenions are only power-associative. The sedenions and all further ''extensions'' of these four normed division algebras are solely power-associative with non-trivial
zero divisor
In abstract algebra, an element of a ring is called a left zero divisor if there exists a nonzero in such that , or equivalently if the map from to that sends to is not injective. Similarly, an element of a ring is called a right zer ...
vector space
In mathematics and physics, a vector space (also called a linear space) is a set whose elements, often called '' vectors'', may be added together and multiplied ("scaled") by numbers called ''scalars''. Scalars are often real numbers, but can ...
of
dimension
In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. Thus, a line has a dimension of one (1D) because only one coor ...
1, while , , and work in algebraic number fields of dimensions 2, 4, 8, and 16, respectively.
List of basic calculations
Evolution of the Hindu-Arabic digit
Brahmic numerals
The Brahmi numerals are a numeral system attested from the 3rd century BCE (somewhat later in the case of most of the tens). They are a non positional decimal system. They are the direct graphic ancestors of the modern Hindu–Arabic numeral s ...
represented 1, 2, and 3 with as many lines. 4 was simplified by joining its four lines into a cross that looks like the modern plus sign. The
Shunga
is a type of Japanese erotic art typically executed as a kind of ukiyo-e, often in woodblock print format. While rare, there are also extant erotic painted handscrolls which predate ukiyo-e. Translated literally, the Japanese word ''shunga' ...
would add a horizontal line on top of the digit, and the Kshatrapa and Pallava evolved the digit to a point where the speed of writing was a secondary concern. The
Arab
The Arabs (singular: Arab; singular ar, عَرَبِيٌّ, DIN 31635: , , plural ar, عَرَب, DIN 31635: , Arabic pronunciation: ), also known as the Arab people, are an ethnic group mainly inhabiting the Arab world in Western Asia, ...
s' 4 still had the early concept of the cross, but for the sake of efficiency, was made in one stroke by connecting the "western" end to the "northern" end; the "eastern" end was finished off with a curve. The Europeans dropped the finishing curve and gradually made the digit less cursive, ending up with a digit very close to the original Brahmin cross.
While the shape of the character for the digit 4 has an ascender in most modern
typeface
A typeface (or font family) is the design of lettering that can include variations in size, weight (e.g. bold), slope (e.g. italic), width (e.g. condensed), and so on. Each of these variations of the typeface is a font.
There are thousands o ...
s, in typefaces with
text figures
Text figures (also known as non-lining, lowercase, old style, ranging, hanging, medieval, billing, or antique figures or numerals) are numerals designed with varying heights in a fashion that resembles a typical line of running text, hence the ...
the glyph usually has a
descender
In typography and handwriting, a descender is the portion of a letter that extends below the baseline of a font.
For example, in the letter ''y'', the descender is the "tail", or that portion of the diagonal line which lies below the ''v'' c ...
, as, for example, in .
On the
seven-segment display
A seven-segment display is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, basic ...
s of pocket calculators and digital watches, as well as certain
optical character recognition
Optical character recognition or optical character reader (OCR) is the electronic or mechanical conversion of images of typed, handwritten or printed text into machine-encoded text, whether from a scanned document, a photo of a document, a sc ...
fonts, 4 is seen with an open top.
Television station
A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television (ATV) operator, that transmits video content and audio content via radio waves directly from a transmitter on the eart ...
s that operate on
channel 4
Channel 4 is a British free-to-air public broadcast television network operated by the state-owned Channel Four Television Corporation. It began its transmission on 2 November 1982 and was established to provide a fourth television service ...
have occasionally made use of another variation of the "open 4", with the open portion being on the side, rather than the top. This version resembles the Canadian Aboriginal syllabics letter ᔦ. The
magnetic ink character recognition
Magnetic ink character recognition code, known in short as MICR code, is a character recognition technology used mainly by the banking industry to streamline the processing and clearance of cheques and other documents. MICR encoding, called the ' ...
Nirodha
In Buddhism, nirodha, "cessation," "extinction," or "suppression," refers to the cessation or renouncing of craving and desire. It is the third of the Four Noble Truths, stating that suffering ( dukkha) ceases when craving and desire are renoun ...
,
Magga
The Buddhist path (''marga'') to liberation, also referred to as awakening, is described in a wide variety of ways. The classical one is the Noble Eightfold Path, which is only one of several summaries presented in the Sutta Pitaka. A number of ...
*
Four sights
The four sights are four events described in the legendary account of Gautama Buddha's life which led to his realization of the impermanence and the ultimate dissatisfaction of conditioned existence. According to this legend, before these encounte ...
– observations which affected Prince Siddhartha deeply and made him realize the sufferings of all beings, and compelled him to begin his spiritual journey—an old man, a
sick
Sick may refer to:
Medical conditions
* Having a disease or infection
* Vomiting (British)
Music
* The Sick, a Swedish band formed by two members of Dozer
Albums
* Sick (Loaded album), ''Sick'' (Loaded album), 2009
* Sick (Massacra album), ' ...
man, a
dead
Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
,
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
,
fire
Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
At a certain point in the combustion reaction, called the ignition point, flames a ...
, and
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
*
Four Heavenly Kings
The Four Heavenly Kings are four Buddhist gods, each of whom is believed to watch over one cardinal direction of the world. In Chinese mythology, they are known collectively as the "Fēng Tiáo Yǔ Shùn" () or "Sìdà Tiānwáng" (). In the ...
* Four Foundations of Mindfulness – contemplation of the body, contemplation of feelings, contemplation of mind, contemplation of mental objects
*
Four Right Exertions
The Four Right Exertions (also known as, Four Proper Exertions, Four Right Efforts, Four Great Efforts, Four Right Endeavors or Four Right Strivings) (Pali: '; Skt.: ' or ') are an integral part of the Buddhist path to Enlightenment (understan ...
loving-kindness Loving-kindness may refer to:
* an English translation of Chesed
( he, חֶסֶד, also Romanized: ) is a Hebrew word that means 'kindness or love between people', specifically of the devotional piety of people towards God as well as of love o ...
Four stages of enlightenment
The four stages of awakening in Early Buddhism and Theravada
are four progressive stages culminating in full awakening (''Bodhi'') as an Arahant (SN 22.122).
These four stages are Sotāpanna, Sakadāgāmi, Anāgāmi, and Arahant. The oldest ...
arahant
In Buddhism, an ''arhat'' (Sanskrit: अर्हत्) or ''arahant'' (Pali: अरहन्त्, 𑀅𑀭𑀳𑀦𑁆𑀢𑁆) is one who has gained insight into the true nature of existence and has achieved ''Nirvana'' and liberated ...
Lumbini
Lumbinī ( ne, लुम्बिनी, IPA=ˈlumbini , "the lovely") is a Buddhist pilgrimage site in the Rupandehi District of Lumbini Province in Nepal. It is the place where, according to Buddhist tradition, Queen Mahamayadevi gave birth ...
Sarnath
Sarnath (Hindustani pronunciation: aːɾnaːtʰ also referred to as Sarangnath, Isipatana, Rishipattana, Migadaya, or Mrigadava) is a place located northeast of Varanasi, near the confluence of the Ganges and the Varuna rivers in Uttar Pr ...
, and
Kusinara
Kushinagar ( Hindustani: or ; Pali: ; Sanskrit: ) is a town in the Kushinagar district in Uttar Pradesh, India. It is an important and popular Buddhist pilgrimage site, where Buddhists believe Gautama Buddha attained ''parinirvana''.
Etymo ...
Judeo-Christian symbolism
*The
Tetragrammaton
The Tetragrammaton (; ), or Tetragram, is the four-letter Hebrew theonym (transliterated as YHWH), the name of God in the Hebrew Bible. The four letters, written and read from right to left (in Hebrew), are ''yodh'', '' he'', '' waw'', and ...
is the four-letter name of
God
In monotheistic thought, God is usually viewed as the supreme being, creator, and principal object of faith. Swinburne, R.G. "God" in Honderich, Ted. (ed)''The Oxford Companion to Philosophy'', Oxford University Press, 1995. God is typically ...
living creatures
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fungi; ...
: a man, a lion, an ox, and an eagle.
*The four Matriarchs (foremothers) of
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
Rebekah
Rebecca, ; Syriac: , ) from the Hebrew (lit., 'connection'), from Semitic root , 'to tie, couple or join', 'to secure', or 'to snare') () appears in the Hebrew Bible as the wife of Isaac and the mother of Jacob and Esau. According to biblical ...
,
Leah
Leah ''La'ya;'' from (; ) appears in the Hebrew Bible as one of the two wives of the Biblical patriarch Jacob. Leah was Jacob's first wife, and the older sister of his second (and favored) wife Rachel. She is the mother of Jacob's first son ...
, and
Rachel
Rachel () was a Biblical figure, the favorite of Jacob's two wives, and the mother of Joseph and Benjamin, two of the twelve progenitors of the tribes of Israel. Rachel's father was Laban. Her older sister was Leah, Jacob's first wife. Her aun ...
lulav
''Lulav'' (; he, לולב) is a closed frond of the date palm tree. It is one of the Four Species used during the Jewish holiday of Sukkot. The other Species are the '' hadass'' ( myrtle), '' aravah'' (willow), and ''etrog'' (citron). When ...
etrog
Etrog ( he, אֶתְרוֹג, plural: '; Ashkenazi Hebrew: ', plural: ') is the yellow citron or ''Citrus medica'' used by Jews during the week-long holiday of Sukkot as one of the four species. Together with the ''lulav'', ''hadass'', and '' a ...
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
)
*The Four Cups of Wine to drink on the
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
holiday of
Passover
Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...
. (
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
)
*The Four Questions to be asked on the
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
holiday of
Passover
Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...
. (
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
)
*The Four Sons to be dealt with on the
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
holiday of
Passover
Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...
. (
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
)
*The Four Expressions of Redemption to be said on the
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
holiday of
Passover
Passover, also called Pesach (; ), is a major Jewish holiday that celebrates the Biblical story of the Israelites escape from slavery in Egypt, which occurs on the 15th day of the Hebrew month of Nisan, the first month of Aviv, or spring. ...
. (
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
)
*The four
Gospel
Gospel originally meant the Christian message (" the gospel"), but in the 2nd century it came to be used also for the books in which the message was set out. In this sense a gospel can be defined as a loose-knit, episodic narrative of the words a ...
s:
Matthew
Matthew may refer to:
* Matthew (given name)
* Matthew (surname)
* ''Matthew'' (ship), the replica of the ship sailed by John Cabot in 1497
* ''Matthew'' (album), a 2000 album by rapper Kool Keith
* Matthew (elm cultivar), a cultivar of the Ch ...
,
Mark
Mark may refer to:
Currency
* Bosnia and Herzegovina convertible mark, the currency of Bosnia and Herzegovina
* East German mark, the currency of the German Democratic Republic
* Estonian mark, the currency of Estonia between 1918 and 1927
* F ...
John
John is a common English name and surname:
* John (given name)
* John (surname)
John may also refer to:
New Testament
Works
* Gospel of John, a title often shortened to John
* First Epistle of John, often shortened to 1 John
* Secon ...
. (
Christianity
Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. It is the world's largest and most widespread religion with roughly 2.38 billion followers representing one-third of the global pop ...
)
*The
Four Horsemen of the Apocalypse
The Four Horsemen of the Apocalypse are figures in the Christian scriptures, first appearing in the Book of Revelation, a piece of apocalypse literature written by John of Patmos.
Revelation 6 tells of a book or scroll in God's right hand t ...
ride in the
Book of Revelation
The Book of Revelation is the final book of the New Testament (and consequently the final book of the Christian Bible). Its title is derived from the first word of the Koine Greek text: , meaning "unveiling" or "revelation". The Book of ...
. (
Christianity
Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. It is the world's largest and most widespread religion with roughly 2.38 billion followers representing one-third of the global pop ...
Jerusalem
Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس ) (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałēm. i ...
,
Hebron
Hebron ( ar, الخليل or ; he, חֶבְרוֹן ) is a Palestinian. city in the southern West Bank, south of Jerusalem. Nestled in the Judaean Mountains, it lies above sea level. The second-largest city in the West Bank (after Eas ...
Tiberius
Tiberius Julius Caesar Augustus (; 16 November 42 BC – 16 March AD 37) was the second Roman emperor. He reigned from AD 14 until 37, succeeding his stepfather, the first Roman emperor Augustus. Tiberius was born in Rome in 42 BC. His father ...
Hinduism
*There are four
Vedas
upright=1.2, The Vedas are ancient Sanskrit texts of Hinduism. Above: A page from the '' Atharvaveda''.
The Vedas (, , ) are a large body of religious texts originating in ancient India. Composed in Vedic Sanskrit, the texts constitute th ...
: Rigveda, Samaveda, Yajurveda and Atharvaveda.
*In
Puruṣārtha
''Purushartha'' (Sanskrit: पुरुषार्थ, IAST: ) literally means "object(ive) of men".Dharma,
Artha
''Artha'' (; sa, अर्थ; Tamil: ''poruḷ'' / ''பொருள்'') is one of the four aims of human life in Indian philosophy.James Lochtefeld (2002), The Illustrated Encyclopedia of Hinduism, Rosen Publishing, New York, , pp 55–56 ...
,
Kāma
''Kama'' (Sanskrit ) means "desire, wish, longing" in Hindu, Buddhist, Jain, and Sikh literature.Monier Williamsकाम, kāmaMonier-Williams Sanskrit English Dictionary, pp 271, see 3rd column Kama often connotes sensual pleasure, sexua ...
,
Moksha
''Moksha'' (; sa, मोक्ष, '), also called ''vimoksha'', ''vimukti'' and ''mukti'', is a term in Hinduism, Buddhism, Jainism and Sikhism for various forms of emancipation, enlightenment, liberation, and release. In its soteriologic ...
Sannyasa
''Sannyasa'' (Sanskrit: संन्यास; IAST: ), sometimes spelled Sanyasa (सन्न्यास) or Sanyasi (for the person), is life of renunciation and the fourth stage within the Hindu system of four life stages known as '' A ...
(renunciation).
*The four primary castes or strata of society: Brahmana (priest/teacher),
Kshatriya
Kshatriya ( hi, क्षत्रिय) (from Sanskrit ''kṣatra'', "rule, authority") is one of the four varna (social orders) of Hindu society, associated with warrior aristocracy. The Sanskrit term ''kṣatriyaḥ'' is used in the con ...
(warrior/politician),
Vaishya
Vaishya (Sanskrit: वैश्य, ''vaiśya'') is one of the four varnas of the Hindu social order in India. Vaishyas are classed third in the order of caste hierarchy.
The occupation of Vaishyas consists mainly of agriculture, taking care ...
(landowner/entrepreneur) and
Shudra
Shudra or ''Shoodra'' (Sanskrit: ') is one of the four '' varnas'' of the Hindu caste system and social order in ancient India. Various sources translate it into English as a caste, or alternatively as a social class. Theoretically, class ser ...
(servant/manual laborer).
*The swastika symbol is traditionally used in
Hindu
Hindus (; ) are people who religiously adhere to Hinduism. Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
religions as a sign of good luck and signifies good from all four directions.
*The god
Brahma
Brahma ( sa, ब्रह्मा, Brahmā) is a Hindu god, referred to as "the Creator" within the Trimurti, the trinity of supreme divinity that includes Vishnu, and Shiva.Jan Gonda (1969)The Hindu Trinity Anthropos, Bd 63/64, H 1/2, pp. 21 ...
has four faces.
*There are four ''
yuga
A ''yuga'', in Hinduism, is generally used to indicate an age of time.
In the ''Rigveda'', a ''yuga'' refers to generations, a long period, a very brief period, or a yoke (joining of two things). In the ''Mahabharata'', the words ''yuga'' and ...
Treta
''Treta Yuga'', in Hinduism, is the second and second best of the four '' yugas'' (world ages) in a ''Yuga Cycle'', preceded by '' Krita (Satya) Yuga'' and followed by '' Dvapara Yuga''. ''Treta Yuga'' lasts for 1,296,000 years (3,600 divine year ...
'' and ''
Kali
Kali (; sa, काली, ), also referred to as Mahakali, Bhadrakali, and Kalika ( sa, कालिका), is a Hindu goddess who is considered to be the goddess of ultimate power, time, destruction and change in Shaktism. In this tra ...
''
Islam
*
Eid al-Adha
Eid al-Adha () is the second and the larger of the two main holidays celebrated in Islam (the other being Eid al-Fitr). It honours the willingness of Ibrahim (Abraham) to sacrifice his son Ismail (Ishmael) as an act of obedience to Allah's com ...
lasts for four days, from the 10th to the 14th of
Dhul Hijja
Dhu al-Hijja ( ar, ذُو ٱلْحِجَّة, translit=Ḏū al-Ḥijja, ), also spelled Zu al-Hijja, is the twelfth and final month in the Islamic calendar. It is a very sacred month in the Islamic calendar, one in which the '' Ḥajj'' (Pilgri ...
Caliph
A caliphate or khilāfah ( ar, خِلَافَة, ) is an institution or public office under the leadership of an Islamic steward with the title of caliph (; ar, خَلِيفَة , ), a person considered a political-religious successor to th ...
s:
Abu Bakr
Abu Bakr Abdallah ibn Uthman Abi Quhafa (; – 23 August 634) was the senior companion and was, through his daughter Aisha, a father-in-law of the Islamic prophet Muhammad, as well as the first caliph of Islam. He is known with the honor ...
,
Umar ibn al-Khattab
ʿUmar ibn al-Khaṭṭāb ( ar, عمر بن الخطاب, also spelled Omar, ) was the second Rashidun caliph, ruling from August 634 until his assassination in 644. He succeeded Abu Bakr () as the second caliph of the Rashidun Caliphate ...
,
Uthman ibn Affan
Uthman ibn Affan ( ar, عثمان بن عفان, ʿUthmān ibn ʿAffān; – 17 June 656), also spelled by Colloquial Arabic, Turkish and Persian rendering Osman, was a second cousin, son-in-law and notable companion of the Islamic prop ...
and Ali ibn Abi Talib.
*The Four Arch Angels in Islam are: Jibraeel (Gabriel), Mikaeel (Michael), Izraeel (Azrael), and Israfil (Raphael)
*There are four months in which war is not permitted:
Muharram
Muḥarram ( ar, ٱلْمُحَرَّم) (fully known as Muharram ul Haram) is the first month of the Islamic calendar. It is one of the four sacred months of the year when warfare is forbidden. It is held to be the second holiest month after ...
,
Rajab
Rajab ( ar, رَجَب) is the seventh month of the Islamic calendar. The lexical definition of the classical Arabic verb ''rajaba'' is "to respect" which could also mean "be awe or be in fear", of which Rajab is a derivative.
This month is re ...
,
Dhu al-Qi'dah
Dhu al-Qa'dah ( ar, ذُو ٱلْقَعْدَة, ', ), also spelled Dhu al-Qi'dah or Zu al-Qa'dah, is the eleventh month in the Islamic calendar.
It could possibly mean "possessor or owner of the sitting and seating place" - the space occupied w ...
fiqh
''Fiqh'' (; ar, فقه ) is Islamic jurisprudence. Muhammad-> Companions-> Followers-> Fiqh.
The commands and prohibitions chosen by God were revealed through the agency of the Prophet in both the Quran and the Sunnah (words, deeds, and ...
:
Hanafi
The Hanafi school ( ar, حَنَفِية, translit=Ḥanafiyah; also called Hanafite in English), Hanafism, or the Hanafi fiqh, is the oldest and one of the four traditional major Sunni schools ( maddhab) of Islamic Law (Fiqh). It is named a ...
,
Shafi`i
The Shafii ( ar, شَافِعِي, translit=Shāfiʿī, also spelled Shafei) school, also known as Madhhab al-Shāfiʿī, is one of the four major traditional schools of religious law (madhhab) in the Sunnī branch of Islam. It was founded by ...
,
Maliki
The ( ar, مَالِكِي) school is one of the four major schools of Islamic jurisprudence within Sunni Islam. It was founded by Malik ibn Anas in the 8th century. The Maliki school of jurisprudence relies on the Quran and hadiths as primary ...
and
Hanbali
The Hanbali school ( ar, ٱلْمَذْهَب ٱلْحَنۢبَلِي, al-maḏhab al-ḥanbalī) is one of the four major traditional Sunni schools (''madhahib'') of Islamic jurisprudence. It is named after the Arab scholar Ahmad ibn Hanbal ...
.
*There are four major Sunni Imams:
Abū Ḥanīfa
Nuʿmān ibn Thābit ibn Zūṭā ibn Marzubān ( ar, نعمان بن ثابت بن زوطا بن مرزبان; –767), commonly known by his '' kunya'' Abū Ḥanīfa ( ar, أبو حنيفة), or reverently as Imam Abū Ḥanīfa by Sunni Musl ...
,
Muhammad ibn Idris ash-Shafi`i
Abū ʿAbdillāh Muḥammad ibn Idrīs al-Shāfiʿī ( ar, أَبُو عَبْدِ ٱللهِ مُحَمَّدُ بْنُ إِدْرِيسَ ٱلشَّافِعِيُّ, 767–19 January 820 CE) was an Arab Muslim theologian, writer, and schola ...
,
Malik ibn Anas
Malik ibn Anas ( ar, مَالِك بن أَنَس, 711–795 CE / 93–179 AH), whose full name is Mālik bin Anas bin Mālik bin Abī ʿĀmir bin ʿAmr bin Al-Ḥārith bin Ghaymān bin Khuthayn bin ʿAmr bin Al-Ḥārith al-Aṣbaḥī ...
and
Ahmad ibn Hanbal
Ahmad ibn Hanbal al-Dhuhli ( ar, أَحْمَد بْن حَنْبَل الذهلي, translit=Aḥmad ibn Ḥanbal al-Dhuhlī; November 780 – 2 August 855 CE/164–241 AH), was a Muslim jurist, theologian, ascetic, hadith traditionist, and ...
.
*There are four books in Islam: Taurait, Zaboor, Injeel, Quran.
*Waiting for four months is ordained for those who take an oath for abstention from their wives.
*The waiting period of the woman whose husband dies is four months and ten days.
*When Abraham said: "My Lord, show me how You give life to the dead," Allah said: "Why! Do you have no faith?" Abraham replied: "Yes, but in order that my heart be at rest." He said: "Then take four birds, and tame them to yourself, then put a part of them on every hill, and summon them; they will come to you flying. l-Baqara 2:260*The respite of four months was granted to give time to the mushriks in Surah
At-Tawba
At-Tawbah ( ar, ٱلتوبة, ; The Repentance), also known as Bara'ah ( ar, براءة, ; Repudiation), is the ninth chapter ('' sūrah'') of the Quran. It contains 129 verses ('' āyāt'') and is one of the last Medinan surahs.
This Surah i ...
so that they should consider their position carefully and decide whether to make preparation for war or to emigrate from the country or to accept Islam.
*Those who accuse honorable women (of unchastity) but do not produce four witnesses, flog them with eighty lashes, and do not admit their testimony ever after. They are indeed transgressors. n-Noor 24:4
Taoism
*
Four Symbols
The Four Symbols (, literally meaning "four images"), are four mythological creatures appearing among the Chinese constellations along the ecliptic, and viewed as the guardians of the four cardinal directions. These four creatures are also ref ...
*In a more general sense, numerous mythological and cosmogonical systems consider
Four corners of the world
Several cosmological and mythological systems portray four corners of the world or four quarters of the world corresponding approximately to the four points of the compass (or the two solstices and two equinoxes). At the center may lie a sacr ...
as essentially corresponding to the four points of the compass.
*Four is the sacred number of the
Zia
Zia or ZIA (also spelled Ziya, Ḍiya , Dia or Diya) may refer to:
People
* Zia (name), including a list of people and fictional characters with the name
** A romanization of the Wu ( Shanghainese) pronunciation of the Chinese surname Xie (謝)
...
, an indigenous tribe located in the U.S. state of
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe
, LargestCity = Albuquerque
, LargestMetro = Tiguex
, OfficialLang = None
, Languages = English, Spanish ( New Mexican), Navajo, Ke ...
homonym
In linguistics, homonyms are words which are homographs (words that share the same spelling, regardless of pronunciation), or homophones ( equivocal words, that share the same pronunciation, regardless of spelling), or both. Using this definiti ...
for "death" in their languages.
*In
Slavic mythology
Slavic mythology or Slavic religion is the religious beliefs, myths, and ritual practices of the Slavs before Christianisation, which occurred at various stages between the 8th and the 13th century. The South Slavs, who likely settled in the Balk ...
Four Freedoms
The Four Freedoms were goals articulated by U.S. President Franklin D. Roosevelt on Monday, January 6, 1941. In an address known as the Four Freedoms speech (technically the 1941 State of the Union address), he proposed four fundamental freed ...
: four fundamental freedoms that
Franklin D. Roosevelt
Franklin Delano Roosevelt (; ; January 30, 1882April 12, 1945), often referred to by his initials FDR, was an American politician and attorney who served as the 32nd president of the United States from 1933 until his death in 1945. As the ...
declared ought to be enjoyed by everyone in the world: Freedom of Speech, Freedom of Religion, Freedom from Want, Freedom from Fear.
* Gang of Four: Popular name for four Chinese Communist Party leaders who rose to prominence during China's Cultural Revolution, but were ousted in 1976 following the death of Chairman
Mao Zedong
Mao Zedong pronounced ; also romanised traditionally as Mao Tse-tung. (26 December 1893 – 9 September 1976), also known as Chairman Mao, was a Chinese communist revolutionary who was the founder of the People's Republic of China (PRC) ...
. Among the four was Mao's widow,
Jiang Qing
Jiang Qing (19 March 191414 May 1991), also known as Madame Mao, was a Chinese communist revolutionary, actress, and major political figure during the Cultural Revolution (1966–1976). She was the fourth wife of Mao Zedong, the Chairman of ...
. Since then, many other political factions headed by four people have been called "Gangs of Four".
In computing
*Four
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
s (half a
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
tetramer
A tetramer () ('' tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula ...
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
,
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
, and
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
.
*Four giant gas/ice planets in the
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
:
Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
, and Neptune.
*Four of Jupiter's moons (the Galilean moons) are readily visible from Earth with a hobby telescope.
*
Messier object
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters'').
Because Messier was only in ...
globular cluster
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...
in the constellation
Scorpius
Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation that pre-dates the Gr ...
.
*The Roman numeral IV stands for
subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
nucleobase
Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides, which, in turn, are components of nucleotides, with all of these monomers constituting the basic b ...
adenine
Adenine () ( symbol A or Ade) is a nucleobase (a purine derivative). It is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The three others are guanine, cytosine and thymine. Its deri ...
,
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
,
cytosine
Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an ...
,
thymine
Thymine () ( symbol T or Thy) is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidi ...
(
uracil
Uracil () (symbol U or Ura) is one of the four nucleobases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced b ...
chordate
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...
s have four feet, legs or leglike appendages (
tetrapods
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct therapsi ...
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
Ungulata
Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...
) use four fingers for movement.
*All
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s with wings except
flies
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced m ...
and some others have four
wing
A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...
s.
*Insects of the superorder Endopterygota, also known as Holometabola, such as butterflies, ants, bees, beetles, fleas, flies, moths, and wasps, undergo holometabolism—complete metamorphism in four stages—from (1) embryo (ovum, egg), to (2) larva (such as grub, caterpillar), then (3) pupa (such as the chrysalis), and finally (4) the imago.
*In the common
ABO blood group system
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. For human blood transfusions, it is the most important of the 43 different blood type (or group) classification system ...
, there are four blood types (A, B, O, AB).
*
Humans
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
have four
canines
Canine may refer to:
Zoology and anatomy
* a dog-like Canid animal in the subfamily Caninae
** ''Canis'', a genus including dogs, wolves, coyotes, and jackals
** Dog, the domestic dog
* Canine tooth, in mammalian oral anatomy
People with the surn ...
and four
wisdom teeth
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
.
*The cow's stomach is divided in four digestive compartments: reticulum, rumen, omasum and abomasum.
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
(that is basis of life on the Earth) is four. Also because of its tetrahedral crystal bond structure,
diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
(one of the natural allotropes of carbon) is the hardest known naturally occurring material. It is also the valence of
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
, whose compounds form the majority of the mass of the Earth's crust.
*The
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
of
beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...
*There are four basic states of
matter
In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic part ...
:
solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
Special relativity
In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:
# The laws ...
and
general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
treat nature as four-
dimension
In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. Thus, a line has a dimension of one (1D) because only one coor ...
space
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually cons ...
and one-dimensional
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, ...
are treated together and called
spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...
. Also, any event ''E'' has a
light cone
In special and general relativity, a light cone (or "null cone") is the path that a flash of light, emanating from a single event (localized to a single point in space and a single moment in time) and traveling in all directions, would take thro ...
composed of four zones of possible communication and cause and effect (outside the light cone is strictly incommunicado).
*There are four
fundamental forces
In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four fundamental interactions known to exist: the gravitational and electro ...
(
electromagnetism
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...
weak nuclear force
In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction ...
, and the
strong nuclear force
The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the ...
distributive lattice
In mathematics, a distributive lattice is a lattice in which the operations of join and meet distribute over each other. The prototypical examples of such structures are collections of sets for which the lattice operations can be given by set ...
.
In logic and philosophy
*The symbolic meanings of the number four are linked to those of the cross and the square. "Almost from prehistoric times, the number four was employed to signify what was solid, what could be touched and felt. Its relationship to the cross (four points) made it an outstanding symbol of wholeness and universality, a symbol which drew all to itself". Where lines of latitude and longitude intersect, they divide the earth into four proportions. Throughout the world kings and chieftains have been called "lord of the four suns" or "lord of the four quarters of the earth", which is understood to refer to the extent of their powers both territorially and in terms of total control of their subjects' doings.
*The Square of Opposition, in both its Aristotelian version and its Boolean version, consists of four forms: A ("All ''S'' is ''R''"), I ("Some ''S'' is ''R''"), E ("No ''S'' is ''R''"), and O ("Some ''S'' is not ''R''").
*In regard to whether two given propositions can have the same
truth value
In logic and mathematics, a truth value, sometimes called a logical value, is a value indicating the relation of a proposition to truth, which in classical logic has only two possible values ('' true'' or '' false'').
Computing
In some pro ...
, there are four separate logical possibilities: the propositions are ''subalterns'' (possibly both are true, and possibly both are false); ''subcontraries'' (both may be true, but not that both are false); ''contraries'' (both may be false, but not that both are true); or ''contradictories'' (it is not possible that both are true, and it is not possible that both are false).
*
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...
held that there are basically
four causes
The four causes or four explanations are, in Aristotelian thought, four fundamental types of answer to the question "why?", in analysis of change or movement in nature: the material, the formal, the efficient, and the final. Aristotle wrote th ...
in nature: the
material
Material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical and chemical properties, or on their geolo ...
final
Final, Finals or The Final may refer to:
* Final (competition), the last or championship round of a sporting competition, match, game, or other contest which decides a winner for an event
** Another term for playoffs, describing a sequence of con ...
categories
Category, plural categories, may refer to:
Philosophy and general uses
*Categorization, categories in cognitive science, information science and generally
*Category of being
* ''Categories'' (Aristotle)
*Category (Kant)
* Categories (Peirce)
* ...
, all viewed as bodies (substantial and insubstantial): (1) ''substance'' in the sense of substrate, primary formless matter; (2) ''quality'', matter's organization to differentiate and individualize something, and coming down to a physical ingredient such as ''pneuma'', breath; (3) ''somehow holding'' (or ''disposed''), as in a posture, state, shape, size, action, and (4) ''somehow holding'' (or ''disposed'') ''toward something,'' as in relative location, familial relation, and so forth.
*
Immanuel Kant
Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and ...
expounded a table of judgments involving four three-way alternatives, in regard to (1) Quantity, (2) Quality, (3) Relation, (4) Modality, and, based thereupon, a table of four categories, named by the terms just listed, and each with three subcategories.
* Arthur Schopenhauer's doctoral thesis was ''
On the Fourfold Root of the Principle of Sufficient Reason
''On the Fourfold Root of the Principle of Sufficient Reason'' (german: Ueber die vierfache Wurzel des Satzes vom zureichenden Grunde) is an elaboration on the classical Principle of Sufficient Reason, written by German philosopher Arthur Schope ...
''.
*
Franz Brentano
Franz Clemens Honoratus Hermann Josef Brentano (; ; 16 January 1838 – 17 March 1917) was an influential German philosopher, psychologist, and former Catholic priest (withdrawn in 1873 due to the definition of papal infallibility in matters ...
held that any major philosophical period has four phases: (1) Creative and rapidly progressing with scientific interest and results; then declining through the remaining phases, (2) practical, (3) increasingly skeptical, and (4) literary, mystical, and scientifically worthless—until philosophy is renewed through a new period's first phase. (See Brentano's essay "The Four Phases of Philosophy and Its Current State" 1895, tr. by Mezei and Smith 1998.)
*
C. S. Peirce
Charles Sanders Peirce ( ; September 10, 1839 – April 19, 1914) was an American philosopher, logician, mathematician and scientist who is sometimes known as "the father of pragmatism".
Educated as a chemist and employed as a scientist for t ...
, usually a trichotomist, discussed four methods for overcoming troublesome uncertainties and achieving secure beliefs: (1) the method of tenacity (policy of sticking to initial belief), (2) the method of authority, (3) the method of congruity (following a fashionable paradigm), and (4) the fallibilistic, self-correcting method of science (see " The Fixation of Belief", 1877); and four barriers to inquiry, barriers refused by the fallibilist: (1) assertion of absolute certainty; (2) maintaining that something is unknowable; (3) maintaining that something is inexplicable because absolutely basic or ultimate; (4) holding that perfect exactitude is possible, especially such as to quite preclude unusual and anomalous phenomena (see F.R.L. irst Rule of Logic 1899).
* Paul Weiss built a system involving four modes of being: Actualities (substances in the sense of substantial, spatiotemporally finite beings), Ideality or Possibility (pure normative form), Existence (the dynamic field), and God (unity). (See Weiss's ''Modes of Being'', 1958).
* Karl Popper outlined a tetradic schema to describe the growth of theories and, via generalization, also the emergence of new behaviors and living organisms: (1) problem, (2) tentative theory, (3) (attempted) error-elimination (especially by way of critical discussion), and (4) new problem(s). (See Popper's ''Objective Knowledge'', 1972, revised 1979.)
*
John Boyd (military strategist)
John Richard Boyd (January 23, 1927 – March 9, 1997) was a United States Air Force fighter pilot and Pentagon consultant during the second half of the 20th century. His theories have been highly influential in military, business, and litiga ...
made his key concept the decision cycle or
OODA loop
The OODA loop is the cycle ''observe–orient–decide–act'', developed by military strategist and United States Air Force Colonel John Boyd. Boyd applied the concept to the combat operations process, often at the operational level during m ...
, consisting of four stages: (1) observation (data intake through the senses), (2) orientation (analysis and synthesis of data), (3) decision, and (4) action. Boyd held that his decision cycle has philosophical generality, though for strategists the point remains that, through swift decisions, one can disrupt an opponent's decision cycle.
*
Richard McKeon
Richard McKeon (; April 26, 1900 – March 31, 1985) was an American philosopher and longtime professor at the University of Chicago. His ideas formed the basis for the UN's Universal Declaration of Human Rights.
Life, times, and influences
McKeo ...
outlined four classes (each with four subclasses) of modes of philosophical inquiry: (1) Modes of Being (Being); (2) Modes of Thought (That which is); (3) Modes of Fact (Existence); (4) Modes of Simplicity (Experience)—and, corresponding to them, four classes (each with four subclasses) of philosophical semantics: Principles, Methods, Interpretations, and Selections. (See McKeon's "Philosophic Semantics and Philosophic Inquiry" in ''Freedom and History and Other Essays'', 1989.)
* Jonathan Lowe (E.J. Lowe) argues in ''The Four-Category Ontology'', 2006, for four categories: ''kinds'' (substantial universals), ''attributes'' (relational universals and property-universals), ''objects'' (substantial particulars), and ''modes'' (relational particulars and property-particulars, also known as " tropes"). (See Lowe's "Recent Advances in Metaphysics," 2001 Eprint
*Four opposed camps of the morality and nature of evil:
moral absolutism
Moral absolutism is an ethical view that some (potentially all) actions are intrinsically right or wrong. Stealing, for instance, might be considered to be always immoral, even if done for the well-being of others (e.g., stealing food to feed a ...
,
amoralism
Moral nihilism (also known as ethical nihilism) is the meta-ethical view that nothing is morally right or wrong.
Moral nihilism is distinct from moral relativism, which allows for actions to be wrong relative to a particular culture or indivi ...
resin identification code
The ASTM International Resin Identification Coding System, often abbreviated RIC, is a set of symbols appearing on plastic products that identify the plastic resin out of which the product is made. It was developed in 1988 by the Society of t ...
used in recycling to identify
low-density polyethylene
Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its ...
CMYK
The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
) is used for
printing
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ...
.
*Wide use of rectangles (with four angles and four sides) because they have effective form and capability for close adjacency to each other (houses, rooms, tables, bricks, sheets of paper, screens, film frames).
*In the Rich Text Format specification, language code 4 is for the
Chinese language
Chinese (, especially when referring to written Chinese) is a group of languages spoken natively by the ethnic Han Chinese majority and many minority ethnic groups in Greater China. About 1.3 billion people (or approximately 16% of the ...
. Codes for regional variants of Chinese are congruent to .
*
Credit card
A credit card is a payment card issued to users (cardholders) to enable the cardholder to pay a merchant for goods and services based on the cardholder's accrued debt (i.e., promise to the card issuer to pay them for the amounts plus the o ...
machines have four-twelve function keys.
*On most phones, the 4 key is associated with the letters G, H, and I, but on the BlackBerry Pearl, it is the key for D and F.
*On many
computer keyboard
A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Replacing early punched cards and paper tape technolog ...
s, the "4" key may also be used to type the
dollar sign
The dollar sign, also known as peso sign, is a symbol consisting of a capital " S" crossed with one or two vertical strokes ($ or ), used to indicate the unit of various currencies around the world, including most currencies denominated "p ...
($) if the
shift key
The Shift key is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters. There are typically two shift keys, on the left and right sides of the row below the home row. The Shift key's name originated f ...
is held down.
*It is the number of
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
*In internet slang, "4" can replace the word "for" (as "four" and "for" are pronounced similarly). For example, typing "4u" instead of "for you".
*In
Leet
Leet (or "1337"), also known as eleet or leetspeak, is a system of modified spellings used primarily on the Internet. It often uses character replacements in ways that play on the similarity of their glyphs via reflection or other resemblance. ...
speak, "4" may be used to replace the letter "A".
*The
TCP/IP stack
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
consists of four layers.
In transport
*Many
internal combustion engines
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combust ...
are called four-stroke engines because they complete one thermodynamic cycle in four distinct steps: Intake, compression, power, and exhaust.
*Most
vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...
commercial vehicle
A commercial vehicle is any type of motor vehicle used for transporting goods or paying passengers.
The United States defines a "commercial motor vehicle" as any self-propelled or towed vehicle used on a public highway in interstate commerce to t ...
s have four road wheels.
*" Quattro", meaning four in the Italian language, is used by
Audi
Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide.
Th ...
as a trademark to indicate that
all-wheel drive
An all-wheel drive vehicle (AWD vehicle) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand.
The most common forms of all-wheel drive are:
;1x1 : All unicycles Reflecting one axle with one w ...
(AWD) technologies are used on Audi-branded cars. The word "Quattro" was initially used by Audi in 1980 in its original 4WD coupé, the
Audi Quattro
The Audi Quattro is a road and rally car, produced by the German automobile manufacturer Audi, part of the Volkswagen Group. It was first shown at the 1980 Geneva Motor Show on 3 March. Production continued through 1991.
Background
The wo ...
. Audi also has a privately held subsidiary company called
quattro GmbH
Audi Sport GmbH, formerly known as quattro GmbH,Audi-Mediacente ...
.
*
List of highways numbered 4
Route 4, or Highway 4, may refer to several highways in the following countries:
International
* AH4, Asian Highway 4
* European route E04
* European route E004
* Cairo – Cape Town Highway
Albania
* SH-4 road in Albania from Durres to Kakav ...
interchanges
Interchange may refer to:
Transport
* Interchange (road), a collection of ramps, exits, and entrances between two or more highways
* Interchange (freight rail), the transfer of freight cars between railroad companies
* Interchange station, a rai ...
" (substitute players), who can be freely substituted at any time, subject to a limit on the total number of substitutions.
*In
baseball
Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding t ...
third base
A third baseman, abbreviated 3B, is the player in baseball or softball whose responsibility is to defend the area nearest to third base — the third of four bases a baserunner must touch in succession to score a run. In the scoring system us ...
, and
home plate
A baseball field, also called a ball field or baseball diamond, is the field upon which the game of baseball is played. The term can also be used as a metonym for a baseball park. The term sandlot is sometimes used, although this usually refers ...
; to score a run, an offensive player must complete, in the sequence shown, a circuit of those four bases.
** When a batter receives four pitches that the umpire declares to be " balls" in a single at-bat, a base on balls, informally known as a "walk", is awarded, with the batter sent to first base.
**For scoring, number 4 is assigned to the second baseman.
**Four is the most runs that can be scored on any single at bat, whereby all three baserunners and the batter score (the most common being via a
grand slam
Grand Slam most often refers to:
* Grand Slam (tennis), one player or pair winning all four major annual tournaments, or the tournaments themselves
Grand Slam or Grand slam may also refer to:
Games and sports
* Grand slam, winning category te ...
).
**The fourth batter in the batting lineup is called the
cleanup hitter
In baseball, a cleanup hitter is the fourth hitter in the batting order. The cleanup hitter is traditionally the team's most powerful hitter. His job is to "clean up the bases", i.e., drive in base runners.
Theory
The thinking behind the us ...
.
*In
basketball
Basketball is a team sport in which two teams, most commonly of five players each, opposing one another on a rectangular court, compete with the primary objective of shooting a basketball (approximately in diameter) through the defender's h ...
, the number four is used to designate the
power forward
The power forward (PF), also known as the four, is one of the five traditional positions in a regulation basketball game. Traditionally, power forwards have played a role similar to centers. When on offense, they typically play with their ba ...
position, often referred to as "the four spot" or "the four".
*In
cricket
Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by str ...
, a four is a specific type of scoring event, whereby the ball crosses the
boundary
Boundary or Boundaries may refer to:
* Border, in political geography
Entertainment
* ''Boundaries'' (2016 film), a 2016 Canadian film
* ''Boundaries'' (2018 film), a 2018 American-Canadian road trip film
*Boundary (cricket), the edge of the pla ...
after touching the ground at least one time, scoring four runs. Taking four wickets in four consecutive balls is typically referred to as a double hat trick (two consecutive, overlapping hat tricks).
*In
American Football
American football (referred to simply as football in the United States and Canada), also known as gridiron, is a team sport played by two teams of eleven players on a rectangular field with goalposts at each end. The offense, the team wi ...
teams get four downs to reach the line of gain.
*In
rowing
Rowing is the act of propelling a human-powered watercraft using the sweeping motions of oars to displace water and generate reactional propulsion. Rowing is functionally similar to paddling, but rowing requires oars to be mechanically ...
, a four refers to a
boat
A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats.
Small boats are typically found on inl ...
for four rowers, with or without
coxswain
The coxswain ( , or ) is the person in charge of a boat, particularly its navigation and steering. The etymology of the word gives a literal meaning of "boat servant" since it comes from ''cock'', referring to the cockboat, a type of ship's boa ...
. In rowing nomenclature, 4− represents a coxless four and 4+ represents a coxed four.
*In
rugby league
Rugby league football, commonly known as just rugby league and sometimes football, footy, rugby or league, is a full-contact sport played by two teams of thirteen players on a rectangular field measuring 68 metres (75 yards) wide and 11 ...
:
** A
try
Try or TRY may refer to:
Music Albums
* ''Try!'', an album by the John Mayer Trio
* ''Try'' (Bebo Norman album) (2014) Songs
* "Try" (Blue Rodeo song) (1987)
* "Try" (Colbie Caillat song) (2014)
* "Try" (Nelly Furtado song) (2004)
* " Try (Ju ...
is worth 4 points.
** One of the two starting centres wears the jersey number 4. (An exception to this rule is the Super League, which uses static squad numbering.)
*In
rugby union
Rugby union, commonly known simply as rugby, is a close-contact team sport that originated at Rugby School in the first half of the 19th century. One of the two codes of rugby football, it is based on running with the ball in hand. In it ...
:
** One of the two starting
locks
Lock(s) may refer to:
Common meanings
*Lock and key, a mechanical device used to secure items of importance
*Lock (water navigation), a device for boats to transit between different levels of water, as in a canal
Arts and entertainment
* ''Lock ...
wears the jersey number 4.
** In the standard bonus points system, a point is awarded in the league standings to a team that scores at least 4 tries in a match, regardless of the match result.
In other fields
* The phrase "
four-letter word
The phrase four-letter word refers to a set of English-language words written with four letters which are considered profane, including common popular or slang terms for excretory functions, sexual activity and genitalia, blasphemies, terms ...
English language
English is a West Germanic language of the Indo-European language family, with its earliest forms spoken by the inhabitants of early medieval England. It is named after the Angles, one of the ancient Germanic peoples that migrated to the ...
.
*Four is the only number whose name in English has the same number of letters as its value.
*Four (, formal writing: ,
pinyin
Hanyu Pinyin (), often shortened to just pinyin, is the official romanization system for Standard Chinese, Standard Mandarin Chinese in China, and to some extent, in Singapore and Malaysia. It is often used to teach Mandarin, normally writte ...
Chinese
Chinese can refer to:
* Something related to China
* Chinese people, people of Chinese nationality, citizenship, and/or ethnicity
**''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation
** List of ethnic groups in China, people of ...
,
Korean
Korean may refer to:
People and culture
* Koreans, ethnic group originating in the Korean Peninsula
* Korean cuisine
* Korean culture
* Korean language
**Korean alphabet, known as Hangul or Chosŏn'gŭl
**Korean dialects and the Jeju language
** ...
,
Vietnamese
Vietnamese may refer to:
* Something of, from, or related to Vietnam, a country in Southeast Asia
** A citizen of Vietnam. See Demographics of Vietnam.
* Vietnamese people, or Kinh people, a Southeast Asian ethnic group native to Vietnam
** Overse ...
and
Japanese
Japanese may refer to:
* Something from or related to Japan, an island country in East Asia
* Japanese language, spoken mainly in Japan
* Japanese people, the ethnic group that identifies with Japan through ancestry or culture
** Japanese diaspor ...
cultures mostly in Eastern Asia because it sounds like the word "death" (,
pinyin
Hanyu Pinyin (), often shortened to just pinyin, is the official romanization system for Standard Chinese, Standard Mandarin Chinese in China, and to some extent, in Singapore and Malaysia. It is often used to teach Mandarin, normally writte ...
sǐ). To avoid complaints from people with tetraphobia, many numbered product lines skip the "four": e.g.
Nokia
Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finland, i ...
cell phones
A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...
(there was no series beginning with a 4 until the Nokia 4.2),
Palm
Palm most commonly refers to:
* Palm of the hand, the central region of the front of the hand
* Palm plants, of family Arecaceae
**List of Arecaceae genera
* Several other plants known as "palm"
Palm or Palms may also refer to:
Music
* Palm (ba ...
PDAs, etc. Some buildings skip floor 4 or replace the number with the letter "F", particularly in heavily Asian areas. ''See
tetraphobia
Tetraphobia () is the practice of avoiding instances of the digit . It is a superstition most common in East Asian nations.
__TOC__
Rationale
The Chinese word for "four" (, pinyin: sì, jyutping: sei3), sounds quite similar to the word for " ...
'' and ''
Numbers in Chinese culture
Some numbers are believed by some to be auspicious or lucky (吉利, ) or inauspicious or unlucky (不吉, ) based on the Chinese word that the number sounds similar to. The numbers 3, 6, and 8 are generally considered to be lucky, while 4 is ...
pseudocience
Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or unfalsifiable claim ...
) the number 4 represents security and stability.
*The number of characters in a canonical four-character idiom.
*In the
NATO phonetic alphabet
The (International) Radiotelephony Spelling Alphabet, commonly known as the NATO phonetic alphabet, is the most widely used set of clear code words for communicating the letters of the Roman alphabet, technically a ''radiotelephonic spellin ...
, the digit 4 is called "fower".
*In
astrology
Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of celestial objects. Di ...
,
Cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
is the 4th
astrological sign
In Western astrology, astrological signs are the twelve 30-degree sectors that make up Earth's 360-degree orbit around the Sun. The signs enumerate from the first day of spring, known as the First Point of Aries, which is the vernal equinox. ...
of the
Zodiac
The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The pat ...
.
*In
Tarot
The tarot (, first known as '' trionfi'' and later as ''tarocchi'' or ''tarocks'') is a pack of playing cards, used from at least the mid-15th century in various parts of Europe to play card games such as Tarocchini. From their Italian roots ...
trump
Trump most commonly refers to:
* Donald Trump (born 1946), 45th president of the United States (2017–2021)
* Trump (card games), any playing card given an ad-hoc high rank
Trump may also refer to:
Businesses and organizations
* Donald J. T ...
or
Major Arcana
The Major Arcana are the named or numbered cards in a cartomantic tarot pack, the name being originally given by occultists to the trump cards of a normal tarot pack used for playing card games. There are usually 22 such cards in a standard 78-car ...
card.
*In ''Tetris'', a game named for the Greek word for 4, every shape in the game is formed of 4 blocks each.
*4 represents the number of Justices on the Supreme Court of the United States necessary to grant a writ of certiorari (i.e., agree to hear a case; it is one less than the number necessary to render a majority decision) at the court's current size.
*Number Four is a character in the book series ''Lorien Legacies.''
*In the performing arts, the fourth wall is an imaginary barrier which separates the audience from the performers, and is "broken" when performers communicate directly to the audience.
In music
*In written music, Time signature, common time is constructed of four beats per measure and a quarter note receives one beat.
*In popular or Popular music, modern music, the most common time signature is also founded on four beats, i.e., 4/4 having four quarter note beats.
*The common major scale is built on two sets of four notes (e.g., CDEF, GABC), where the first and last notes create an octave interval (a pair-of-four relationship).
*The interval of a perfect fourth is a foundational element of many genres of music, represented in music theory as the tonic (music), tonic and subdominant relationship. Four is also embodied within the circle of fifths (also known as circle of fourths), which reveals the interval of four in more active harmonic contexts.
*The typical number of movements in a symphony.
*The number of completed, numbered symphonies by Johannes Brahms.
*The number of strings on a violin, a viola, a cello, double bass, a cuatro (instrument), cuatro, a typical bass guitar, and a ukulele, and the number of string pairs on a mandolin.
*"Four calling birds" is the gift on the fourth day of Christmas in the carol "The Twelve Days of Christmas (song), The Twelve Days of Christmas".
Groups of four
* Big Four (disambiguation)
*Four basic operations of arithmetic: addition, subtraction, multiplication, division (mathematics), division.
*Classical element#Classical elements in Greece, Greek classical elements (fire, air, water, earth).
*Season, Four seasons: spring (season), spring, summer, autumn, winter.
*The Four Seasons (disambiguation)
*A leap year generally occurs every four years.
*Approximately four weeks (4 times 7 days) to a lunar month (synodic month = 29.53 days). Thus the number four is universally an integral part of primitive sacred calendars.
*Four weeks of Advent (and four Advent candles on the Advent wreath).
*Four cardinal directions: north, south, east, west.
*Four Temperaments: sanguine, choleric, Melancholia, melancholic, phlegmatic.
*Humorism, Four Humors: blood, yellow bile, black bile, phlegm.
*Four Great Ancient Capitals of China.
*Four-corner method.
*Four Asian Tigers, referring to the economies of Hong Kong, Taiwan, South Korea, and Singapore
*Four cardinal principles, Cardinal principles.
*Four cardinal virtues: justice, prudence, temperance, fortitude.
*Four suit (cards), suits of playing cards: hearts, diamonds, clubs, spades.
*Four nations of the United Kingdom: England, Wales, Scotland, Northern Ireland.
*Four provinces of Ireland: Munster, Ulster, Leinster, Connacht.
*Four estates: politics, public administration, administration, judiciary, journalism. Especially in the expression "Fourth Estate", which means journalism.
*Four Corners Monument, Four Corners is the only location in the United States where four U.S. state, states come together at a single point: Colorado, Utah,
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe
, LargestCity = Albuquerque
, LargestMetro = Tiguex
, OfficialLang = None
, Languages = English, Spanish ( New Mexican), Navajo, Ke ...
, and Arizona.
* Four Evangelists – Matthew the Apostle, Matthew, Mark the Evangelist, Mark, Luke the Evangelist, Luke, and John the Evangelist, John
* Four Doctor of the Church, Doctors of Western Church – Saint Gregory the Great, Saint Ambrose, Saint Augustine, and Saint Jerome
* Four Doctors of Eastern Church – Saint John Chrysostom, Saint Basil the Great, and Gregory of Nazianzus and Saint Athanasius
* Four Galilean moons of Jupiter – Io (moon), Io, Europa (moon), Europa, Ganymede (moon), Ganymede, and Callisto (moon), Callisto
* The Gang of Four was a Communist Party of China, Chinese communist political faction.
* The Fantastic Four: Mr. Fantastic, The Invisible Woman, The Human Torch, The Thing.
* The Teenage Mutant Ninja Turtles: Leonardo, Michelangelo, Donatello, Raphael
* The Beatles were also known as the "Fab Four": John Lennon, Paul McCartney, George Harrison, Ringo Starr.
* Gang of Four (band), Gang of Four is a British post-punk rock and roll, rock band formed in the late 1970s.
* Four rivers in the Garden of Eden (Book of Genesis, Genesis 2:10–14): Pishon (perhaps the Jaxartes or Syr Darya), Gihon (perhaps the Oxus or Amu Darya), Hiddekel (Tigris), and P'rat (Euphrates).
* There are also four years in a single Olympiad (duration between the Olympic Games). Many major international sports competitions follow this cycle, among them the FIFA World Cup and its FIFA Women's World Cup, women's version, the FIBA World Championships for FIBA World Championship, men and FIBA World Championship for Women, women, and the Rugby World Cup.
* There are four limbs on the human body.
* Four Houses of Hogwarts in the Harry Potter series: Gryffindor, Hufflepuff, Ravenclaw, Slytherin.
* Four known continents of the world in the ''A Song of Ice and Fire'' series: Westeros, Essos, Sothoryos, Ulthos.
* Each Grand Prix in Nintendo's ''Mario Kart'' series is divided into four cups and each cup is divided into four courses. The Mushroom Cup, Flower Cup, Star Cup, and Special Cup make up the Nitro Grand Prix, while the Shell Cup, Banana Cup, Leaf Cup, and the Lightning Cup make up the Retro Grand Prix.
See also
*
List of highways numbered 4
Route 4, or Highway 4, may refer to several highways in the following countries:
International
* AH4, Asian Highway 4
* European route E04
* European route E004
* Cairo – Cape Town Highway
Albania
* SH-4 road in Albania from Durres to Kakav ...
References
*Wells, D. ''The Penguin Dictionary of Curious and Interesting Numbers'' London: Penguin Group. (1987): 55–58