
Hume's fork, in
epistemology
Epistemology is the branch of philosophy that examines the nature, origin, and limits of knowledge. Also called "the theory of knowledge", it explores different types of knowledge, such as propositional knowledge about facts, practical knowle ...
, is a tenet elaborating upon
British empiricist philosopher
David Hume
David Hume (; born David Home; – 25 August 1776) was a Scottish philosopher, historian, economist, and essayist who was best known for his highly influential system of empiricism, philosophical scepticism and metaphysical naturalism. Beg ...
's emphatic, 1730s division between "relations of ideas" and "matters of fact."
Antony Flew
Antony Garrard Newton Flew (; 11 February 1923 – 8 April 2010) was an English philosopher. Belonging to the analytic and evidentialist schools of thought, Flew worked on the philosophy of religion. During the course of his career he taught ...
, ''A Dictionary of Philosophy'', rev 2nd edn (New York: St Martin's Press, 1984)
p. 156
[ Georges Dicker]
ch. 2 "Hume's theory of knowledge (I): 'Hume's fork' "
Hume's Epistemology and Metaphysics: An Introduction
' (London & New York: Routledge
Routledge ( ) is a British multinational corporation, multinational publisher. It was founded in 1836 by George Routledge, and specialises in providing academic books, academic journals, journals and online resources in the fields of the humanit ...
, 1998)
p. 41
introducing Kant's formulation of Hume's fork. (Alternatively, ''Hume's fork'' may refer to what is otherwise termed ''
Hume's law'', a tenet of
ethics
Ethics is the philosophy, philosophical study of Morality, moral phenomena. Also called moral philosophy, it investigates Normativity, normative questions about what people ought to do or which behavior is morally right. Its main branches inclu ...
.) As phrased in
Immanuel Kant's 1780s characterization of Hume's thesis, and furthered in the 1930s by the
logical empiricists, Hume's fork asserts that all statements are exclusively either "analytic ''
a priori
('from the earlier') and ('from the later') are Latin phrases used in philosophy to distinguish types of knowledge, Justification (epistemology), justification, or argument by their reliance on experience. knowledge is independent from any ...
''" or "synthetic ''
a posteriori''," which, respectively, are universally true by mere ''definition'' or, however apparently probable, are unknowable without exact ''experience''.
[ Georges Dicker]
"Hume's fork revisited"
'' History of Philosophy Quarterly'', 1991 Oct;8(4):327–342.
By Hume's fork, a statement's ''
meaning'' either is
analytic or is synthetic, the statement's ''truth''—its agreement with
the real world—either is
necessary or is
contingent, and the statement's purported
''knowledge'' either is or is .
An analytic statement is true via its terms' meanings alone, hence
true by definition, like ''Bachelors are unmarried'', whereas a synthetic statement, concerning external states of affairs, may be false, like ''Bachelors age badly''.
[ Georges Rey]
"The analytic/synthetic distinction"
in Edward N. Zalta, ed., ''Stanford Encyclopedia of Philosophy
The ''Stanford Encyclopedia of Philosophy'' (''SEP'') is a freely available online philosophy resource published and maintained by Stanford University, encompassing both an online encyclopedia of philosophy and peer-reviewed original publication ...
'' (Fall 2018). By mere logical
validity, the necessary is true in all
possible worlds, whereas the contingent hinges on the world's state, a
metaphysical
Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of h ...
basis.
And the ''a priori'' is knowable without, whereas the ''a posteriori'' is knowable only upon, experience in the area of interest.
By Hume's fork, sheer conceptual derivations (ostensibly,
logic
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...
and
mathematics
Mathematics is a field of study that discovers and organizes methods, Mathematical theory, theories and theorems that are developed and Mathematical proof, proved for the needs of empirical sciences and mathematics itself. There are many ar ...
), being analytic, are necessary and ''a priori'', whereas assertions of "real existence" and traits, being synthetic, are contingent and ''a posteriori''.
Hume's own, simpler,
distinction concerned the
problem of induction
The problem of induction is a philosophical problem that questions the rationality of predictions about unobserved things based on previous observations. These inferences from the observed to the unobserved are known as "inductive inferences" ...
—that no amount of examination of cases will logically entail the conformity of unexamined cases—and supported Hume's aim to position
humanism
Humanism is a philosophy, philosophical stance that emphasizes the individual and social potential, and Agency (philosophy), agency of human beings, whom it considers the starting point for serious moral and philosophical inquiry.
The me ...
on par with
empirical science while combatting allegedly rampant "sophistry and illusion" by philosophers and religionists.
Being a
transcendental idealist, Kant asserted both the hope of a true
metaphysics
Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of ...
, and a literal view of
Newton's law of universal gravitation
Newton's law of universal gravitation describes gravity as a force by stating that every particle attracts every other particle in the universe with a force that is Proportionality (mathematics)#Direct proportionality, proportional to the product ...
by defying Hume's fork to declare the "
synthetic a priori." In the 1930s, the logical empiricists staked Hume's fork.
[James Fetzer]
"Carl Hempel"
in Edward N. Zalta, ed., ''The Stanford Encyclopedia of Philosophy
The ''Stanford Encyclopedia of Philosophy'' (''SEP'') is a freely available online philosophy resource published and maintained by Stanford University, encompassing both an online encyclopedia of philosophy and peer-reviewed original publication ...
'' (Spring 2013). Yet in the 1950s,
W. V. O Quine undermined its
analytic/synthetic distinction.
And in the 1970s,
Saul Kripke established the
necessary ''a posteriori''. Still, Hume's fork is a useful starting point to anchor philosophical scrutiny.
Hume's theory and Kant's response
Hume's strong
empiricism
In philosophy, empiricism is an epistemological view which holds that true knowledge or justification comes only or primarily from sensory experience and empirical evidence. It is one of several competing views within epistemology, along ...
, as in Hume's fork as well as Hume's
problem of induction
The problem of induction is a philosophical problem that questions the rationality of predictions about unobserved things based on previous observations. These inferences from the observed to the unobserved are known as "inductive inferences" ...
, was taken as a threat to
Newton's theory of motion.
Immanuel Kant
Immanuel Kant (born Emanuel Kant; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher and one of the central Age of Enlightenment, Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works ...
responded with his
Transcendental Idealism
Transcendental idealism is a philosophical system founded by German philosopher Immanuel Kant in the 18th century. Kant's epistemological program is found throughout his '' Critique of Pure Reason'' (1781). By ''transcendental'' (a term that des ...
in his 1781 ''
Critique of Pure Reason
The ''Critique of Pure Reason'' (; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant, in which the author seeks to determine the limits and scope of metaphysics. Also referred to as Kant's "First Critique", it was foll ...
'', where Kant attributed to the mind a causal role in
sensory experience by the mind's aligning the environmental input by arranging those
sense data into the experience of space and time. Kant thus reasoned existence of the synthetic ''a priori''—combining meanings of terms with states of facts, yet known true without experience of the particular instance—replacing the two prongs of Hume's fork with a three-pronged-fork thesis (Kant's pitchfork) and thus saving
Newton's law of universal gravitation
Newton's law of universal gravitation describes gravity as a force by stating that every particle attracts every other particle in the universe with a force that is Proportionality (mathematics)#Direct proportionality, proportional to the product ...
.
In 1919, Newton's theory fell to Einstein's
general theory of relativity. In the late 1920s, the
logical positivists
Logical positivism, also known as logical empiricism or neo-positivism, was a philosophical movement, in the empiricist tradition, that sought to formulate a scientific philosophy in which philosophical discourse would be, in the perception of ...
rejected Kant's synthetic ''a priori'' and asserted Hume's fork, so called, while hinging it at language—the analytic/synthetic division—while presuming that by holding to analyticity, they could develop a
logical syntax entailing both necessity and aprioricity via logic on one side and, on the other side, demand empirical verification, altogether restricting philosophical discourse to claims
verifiable as either
false or true. In the early 1950s,
Willard Van Orman Quine
Willard Van Orman Quine ( ; known to his friends as "Van"; June 25, 1908 – December 25, 2000) was an American philosopher and logician in the analytic tradition, recognized as "one of the most influential philosophers of the twentieth century" ...
undermined the analytic/synthetic division by explicating
ontological relativity
Ontology is the philosophical study of existence, being. It is traditionally understood as the subdiscipline of metaphysics focused on the most general features of reality. As one of the most fundamental concepts, being encompasses all of realit ...
, as every term in any statement has its meaning contingent on a vast network of knowledge and belief, the speaker's conception of the entire world. By the early 1970s,
Saul Kripke established the necessary ''a posteriori'', since if the
Morning Star and the
Evening Star are the same star, they are the same star by necessity, but this is known true by a human only through relevant experience.
Hume's fork remains basic in Anglo-American philosophy. Many deceptions and confusions are foisted by surreptitious or unwitting conversion of a synthetic claim to an analytic claim, rendered true by necessity but merely a tautology, for instance the
''No true Scotsman'' move. Simply put, Hume's fork has limitations. Related concerns are Hume's distinction of demonstrative versus probable reasoning and
Hume's law. Hume makes other, important two-category distinctions, such as
beliefs versus desires and as impressions versus ideas.
Relations of ideas and matters of fact
The first distinction is between two different areas of human study:
:All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, ''relations of ideas'', and ''matters of fact''. Of the first kind are the sciences of
Geometry
Geometry (; ) is a branch of mathematics concerned with properties of space such as the distance, shape, size, and relative position of figures. Geometry is, along with arithmetic, one of the oldest branches of mathematics. A mathematician w ...
,
Algebra
Algebra is a branch of mathematics that deals with abstract systems, known as algebraic structures, and the manipulation of expressions within those systems. It is a generalization of arithmetic that introduces variables and algebraic ope ...
, and
Arithmetic
Arithmetic is an elementary branch of mathematics that deals with numerical operations like addition, subtraction, multiplication, and division. In a wider sense, it also includes exponentiation, extraction of roots, and taking logarithms.
...
...''
hich are
Ij () is a village in Golabar Rural District of the Central District in Ijrud County, Zanjan province, Iran
Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq ...
''discoverable by the mere operation of thought ... Matters of fact, which are the second object of human reason, are not ascertained in the same manner; nor is our evidence of their truth, however great, of a like nature with the foregoing.
::: — ''
An Enquiry Concerning Human Understanding''
[ ''Enquiry Concerning Human Understanding'', Section IV, Part I.]
Hume's fork is often stated in such a way that statements are divided up into two types:
* Statements about ideas. These are
analytic,
necessary, and
knowable ''
a priori
('from the earlier') and ('from the later') are Latin phrases used in philosophy to distinguish types of knowledge, Justification (epistemology), justification, or argument by their reliance on experience. knowledge is independent from any ...
''.
* Statements about the world. These are synthetic,
contingent, and knowable ''
a posteriori''.
In modern terminology, members of the first group are known as
analytic propositions and members of the latter as
synthetic propositions. This terminology comes from
Kant (Introduction to ''
Critique of Pure Reason
The ''Critique of Pure Reason'' (; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant, in which the author seeks to determine the limits and scope of metaphysics. Also referred to as Kant's "First Critique", it was foll ...
'', Section IV).
Into the first class fall statements such as ''"all bodies are extended"'', ''"all bachelors are unmarried"'', and ideas of mathematics and logic. Into the second class fall statements like ''"the sun rises in the morning"'', and ''"all bodies have mass"''.
Hume wants to prove that
certainty
Certainty (also known as epistemic certainty or objective certainty) is the epistemic property of beliefs which a person has no rational grounds for doubting. One standard way of defining epistemic certainty is that a belief is certain if and ...
does not exist in science. First, Hume notes that statements of the second type can never be entirely certain, due to the fallibility of our senses, the possibility of deception (see e.g. the modern
brain in a vat theory) and other arguments made by philosophical skeptics. It is always possible that any given statement about the world is false.
Second, Hume claims that our belief in cause-and-effect relationships between events is not grounded on reason, but rather arises merely by habit or custom. Suppose one states: "Whenever someone on earth lets go of a stone it falls." While we can grant that in every instance thus far when a rock was dropped on Earth it went down, this does not make it logically necessary that in the future rocks will fall when in the same circumstances. Things of this nature rely upon the future conforming to the same principles which governed the past. But that isn't something that we can know based on past experience—all past experience could tell us is that in the past, the future has resembled the past.
Third, Hume notes that relations of ideas can be used only to prove other relations of ideas, and mean nothing outside of the context of how they relate to each other, and therefore tell us nothing about the world. Take the statement "An equilateral triangle has three sides of equal length." While some earlier philosophers (most notably
Plato
Plato ( ; Greek language, Greek: , ; born BC, died 348/347 BC) was an ancient Greek philosopher of the Classical Greece, Classical period who is considered a foundational thinker in Western philosophy and an innovator of the writte ...
and
Descartes) held that logical statements such as these contained the most formal reality, since they are always true and unchanging, Hume held that, while true, they contain no formal reality, because the truth of the statements rests on the definitions of the words involved, and not on actual things in the world, since there is no such thing as a true triangle or exact equality of length in the world. So for this reason, relations of ideas cannot be used to prove matters of fact.
The results claimed by Hume as consequences of his fork are drastic. According to him, relations of ideas can be proved with certainty (by using other relations of ideas), however, they don't really mean anything about the world. Since they don't mean anything about the world, relations of ideas cannot be used to prove matters of fact. Because of this, matters of fact have no certainty and therefore cannot be used to prove anything. Only certain things can be used to prove other things for certain, but only things about the world can be used to prove other things about the world. But since we can't cross the fork, nothing is both certain and about the world, only one or the other, and so it is impossible to prove something about the world with certainty.
If accepted, Hume's fork makes it pointless to try to prove the
existence of God
The existence of God is a subject of debate in the philosophy of religion and theology. A wide variety of arguments for and against the existence of God (with the same or similar arguments also generally being used when talking about the exis ...
(for example) as a matter of fact. If God is not literally made up of physical matter, and does not have an observable effect on the world
lthough virtually all theists believe that God has an observable effect on the world since they believe it is his creation making a statement about God is not a matter of fact. Therefore, a statement about God must be a relation of ideas. In this case if we prove the statement "God exists," it doesn't really tell us anything about the world; it is just playing with words. It is easy to see how Hume's fork voids the causal argument and the
ontological argument for the existence of a non-observable God. However, this does not mean that the validity of Hume's fork would imply that God definitely does not exist, only that it would imply that the existence of God cannot be proven as a matter of fact without worldly evidence.
Hume rejected the idea of any meaningful statement that did not fall into this schema, saying:
If we take in our hand any volume; of divinity
Divinity (from Latin ) refers to the quality, presence, or nature of that which is divine—a term that, before the rise of monotheism, evoked a broad and dynamic field of sacred power. In the ancient world, divinity was not limited to a single ...
or school metaphysics
Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of ...
, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion. — '' An Enquiry Concerning Human Understanding''
Notes
References
*
{{Hume
Concepts in epistemology
Philosophy of language
Conceptual distinctions
David Hume
Humeanism