A principle is a proposition or value that is a guide for behavior or evaluation. In

law Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vario ...

, it is a rule that has to be or usually is to be followed. It can be desirably followed, or it can be an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed. The principles of such a system are understood by its users as the essential characteristics of the system, or reflecting system's designed purpose, and the effective operation or use of which would be impossible if any one of the principles was to be ignored. A system may be explicitly based on and implemented from a document of principles as was done in IBM's 360/370 ''Principles of Operation''. Examples of principles are,

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...

in a number of fields,

least action The stationary-action principle – also known as the principle of least action – is a variational principle that, when applied to the ''action'' of a mechanical system, yields the equations of motion for that system. The principle states that ...

in physics, those in descriptive comprehensive and fundamental law:

doctrine Doctrine (from la, doctrina, meaning "teaching, instruction") is a codification of beliefs or a body of teachings or instructions, taught principles or positions, as the essence of teachings in a given branch of knowledge or in a belief syste ...

s or assumptions forming normative rules of conduct,

separation of church and state The separation of church and state is a philosophical and jurisprudential concept for defining political distance in the relationship between religious organizations and the state. Conceptually, the term refers to the creation of a secular sta ...

in statecraft, the central dogma of molecular biology,

fairness Fairness or being fair can refer to: * Justice * The character in the award-nominated musical comedy '' A Theory of Justice: The Musical.'' * Equity (law), a legal principle allowing for the use of discretion and fairness when applying justice ...

in ethics, etc. In common English, it is a substantive and collective term referring to rule governance, the absence of which, being "unprincipled", is considered a character defect. It may also be used to declare that a reality has diverged from some ideal or norm as when something is said to be true only "in principle" but not in fact.

As law

As moral law

A principle represents values that orient and rule the conduct of persons in a particular society. To "act on principle" is to act in accordance with one's moral ideals. Principles are absorbed in childhood through a process of

socialization In sociology, socialization or socialisation (see spelling differences) is the process of internalizing the norms and ideologies of society. Socialization encompasses both learning and teaching and is thus "the means by which social and cul ...

. There is a presumption of liberty of individuals that is restrained. Exemplary principles include First, do no harm, the golden rule and the

doctrine of the mean The ''Doctrine of the Mean'' or ''Zhongyong'' is one of the Four Books of classical Chinese philosophy and a central doctrine of Confucianism. The text is attributed to Zisi (Kong Ji), the only grandson of Confucius (Kong Zi). It was originall ...

As a juridic law

It represents a set of values that inspire the written norms that organize the life of a society submitting to the powers of an authority, generally the State. The law establishes a legal obligation, in a coercive way; it therefore acts as principle conditioning of the action that limits the liberty of the individuals. See, for examples, the

territorial principle The territorial principle (also territoriality principle) is a principle of public international law which enables a sovereign state to exercise exclusive jurisdiction over individuals and other legal persons within its territory. It includes both ...

, homestead principle, and

precautionary principle The precautionary principle (or precautionary approach) is a broad epistemological, philosophical and legal approach to innovations with potential for causing harm when extensive scientific knowledge on the matter is lacking. It emphasizes caut ...

As scientific law

Archimedes principle Archimedes' principle (also spelled Archimedes's principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' ...

, relating buoyancy to the weight of displaced water, is an early example of a

in science. Another early one developed by Malthus is the ''population principle'', now called the

Malthusian principle Thomas Robert Malthus (; 13/14 February 1766 – 29 December 1834) was an English cleric, scholar and influential economist in the fields of political economy and demography. In his 1798 book '' An Essay on the Principle of Population'', Mal ...

. Freud also wrote on principles, especially the reality principle necessary to keep the id and pleasure principle in check. Biologists use the principle of priority and

principle of Binomial nomenclature A principle is a proposition or value that is a guide for behavior or evaluation. In law, it is a rule that has to be or usually is to be followed. It can be desirably followed, or it can be an inevitable consequence of something, such as the la ...

for precision in naming

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. There are many principles observed in physics, notably in

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosopher ...

which observes the

mediocrity principle The mediocrity principle is the philosophical notion that "if an item is drawn at random from one of several sets or categories, it's more likely to come from the most numerous category than from any one of the less numerous categories". The prin ...

, the anthropic principle, the principle of relativity and the

cosmological principle In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throu ...

. Other well-known principles include the

uncertainty principle In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of mathematical inequalities asserting a fundamental limit to the accuracy with which the values for certain pairs of physic ...

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...

and the

pigeonhole principle In mathematics, the pigeonhole principle states that if items are put into containers, with , then at least one container must contain more than one item. For example, if one has three gloves (and none is ambidextrous/reversible), then there mu ...

and superposition principle in mathematics.

As axiom or logical fundament

Principle of sufficient reason

The principle states that every event has a rational explanation. The principle has a variety of expressions, all of which are perhaps best summarized by the following: :For every entity ''x'', if ''x'' exists, then there is a sufficient explanation for why ''x'' exists. :For every event ''e'', if ''e'' occurs, then there is a sufficient explanation for why ''e'' occurs. :For every proposition ''p'', if ''p'' is true, then there is a sufficient explanation for why ''p'' is true. However, one realizes that in every sentence there is a direct relation between the predicate and the subject. To say that "the Earth is round", corresponds to a direct relation between the subject and the predicate.

Principle of non-contradiction

According to

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 ...

, “It is impossible for the same thing to belong and not to belong at the same time to the same thing and in the same respect.” For example, it is not possible that in exactly the same moment and place, it rains and does not rain.

Principle of excluded middle

The principle of the excluding third or "principium tertium exclusum" is a principle of the traditional logic formulated canonically by

Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of ma ...

as: either ''A'' is ''B'' or ''A'' isn't ''B''. It is read the following way: either ''P'' is true, or its denial ¬''P'' is. It is also known as "''tertium non datur''" ('A third (thing) is not'). Classically it is considered to be one of the most important fundamental principles or laws of thought (along with the principles of identity, non-contradiction and sufficient reason).

References

External links

* * ''Actus Essendi'' and the Habit of the First Principle in Thomas Aquinas (New York: Einsiedler Press, 2019)
/span>. {{Authority control Concepts in epistemology Concepts in ethics Concepts in metaphysics Concepts in the philosophy of mind Concepts in the philosophy of science Metaphysics of mind Ontology