Hume's fork
Encyclopedia
In philosophy
, Hume's fork may be used to refer to one of several distinctions and dilemmas drawn by David Hume
(though which distinction is a matter of some disagreement).
They are:
1) (Most commonly) Hume's distinction between demonstrative and probable reasoning. (see below)
2) Hume's distinction between 'is' and 'ought'. (This is more commonly known as Hume's Law.)
3) Hume's "dilemma of determinism": the problem that our actions are either causally determined or random. In either case, we are not responsible for them.
(Other important two-category distinctions Hume makes are those between beliefs and desires and between impressions and ideas.)
Hume's fork is often stated in such a way that statements are divided up into two types:
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
, Section IV).
Into the first class fall statements such as "2 + 2 = 4", "all bachelors are unmarried", and truths of mathematics and logic. Into the second class fall statements like "the sun rises in the morning", "the Earth has precisely one moon", and "water freezes at 32 degrees Fahrenheit".
However, these last statements, which are seemingly matters of fact, can also be understood to belong to the first category. For example, "the Earth has precisely one moon" can be transliterated as "the third planet from the sun that has one moon has precisely one moon," thus rendering it as tautological as the germane expressions of basic arithmetic such as "2 + 2 = 4".
Hume wants to prove that certainty
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 logically possible that any given statement about the world is false. (Note that statements like "either the Earth has precisely one moon, or not" are really truths of logic, and say nothing about the world).
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 rock, 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 give us any reason to think that in the future, rocks will fall when in the same circumstances. It would give us reason only if we add as a premise that the future will resemble 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
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
(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, 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 (non-material) 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 famously rejected the idea of any meaningful statement that did not fall into this schema, saying:
This same idea has perdured in relatively contemporary schools of philosophy, such as logical positivism
. This general attitude is strikingly present in Alfred Ayer
's logical empiricist work Language, Truth and Logic.
, for example, famously defended the idea of synthetic a priori propositions. W.V.O. Quine also argued against the well-defined distinction between analytic and synthetic propositions required by Hume's fork in his landmark paper Two Dogmas of Empiricism
.
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...
, Hume's fork may be used to refer to one of several distinctions and dilemmas drawn by David Hume
David Hume
David Hume was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and skepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment...
(though which distinction is a matter of some disagreement).
They are:
1) (Most commonly) Hume's distinction between demonstrative and probable reasoning. (see below)
2) Hume's distinction between 'is' and 'ought'. (This is more commonly known as Hume's Law.)
3) Hume's "dilemma of determinism": the problem that our actions are either causally determined or random. In either case, we are not responsible for them.
(Other important two-category distinctions Hume makes are those between beliefs and desires and between impressions and 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 GeometryGeometryGeometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
, AlgebraAlgebraAlgebra is the branch of mathematics concerning the study of the rules of operations and relations, and the constructions and concepts arising from them, including terms, polynomials, equations and algebraic structures...
, and ArithmeticArithmeticArithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...
... [which are] 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 UnderstandingAn Enquiry Concerning Human UnderstandingAn Enquiry Concerning Human Understanding is a book by the Scottish empiricist philosopher David Hume, published in 1748. It was a revision of an earlier effort, Hume's A Treatise of Human Nature, published anonymously in London in 1739–40...
- - An Enquiry Concerning Human Understanding
-
Hume's fork is often stated in such a way that statements are divided up into two types:
- Statements about ideaIdeaIn the most narrow sense, an idea is just whatever is before the mind when one thinks. Very often, ideas are construed as representational images; i.e. images of some object. In other contexts, ideas are taken to be concepts, although abstract concepts do not necessarily appear as images...
s. These are analytic, necessaryModal logicModal logic is a type of formal logic that extends classical propositional and predicate logic to include operators expressing modality. Modals — words that express modalities — qualify a statement. For example, the statement "John is happy" might be qualified by saying that John is...
statements that are knowableKnowledgeKnowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...
a prioriA priori and a posteriori (philosophy)The terms a priori and a posteriori are used in philosophy to distinguish two types of knowledge, justifications or arguments...
. - Statements about the worldWorldWorld is a common name for the whole of human civilization, specifically human experience, history, or the human condition in general, worldwide, i.e. anywhere on Earth....
. These are synthetic, contingentContingency (philosophy)In philosophy and logic, contingency is the status of propositions that are neither true under every possible valuation nor false under every possible valuation . A contingent proposition is neither necessarily true nor necessarily false...
, and knowable a posterioriA PosterioriApart from the album, some additional remixes were released exclusively through the iTunes Store. They are:*"Eppur si muove" – 6:39*"Dreaming of Andromeda" Apart from the album, some additional remixes were released exclusively through the iTunes Store. They are:*"Eppur si muove" (Tocadisco...
.
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
Immanuel Kant
Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....
(Introduction to Critique of Pure Reason
Critique of Pure Reason
The Critique of Pure Reason by Immanuel Kant, first published in 1781, second edition 1787, is considered one of the most influential works in the history of philosophy. Also referred to as Kant's "first critique," it was followed by the Critique of Practical Reason and the Critique of Judgement...
, Section IV).
Into the first class fall statements such as "2 + 2 = 4", "all bachelors are unmarried", and truths of mathematics and logic. Into the second class fall statements like "the sun rises in the morning", "the Earth has precisely one moon", and "water freezes at 32 degrees Fahrenheit".
However, these last statements, which are seemingly matters of fact, can also be understood to belong to the first category. For example, "the Earth has precisely one moon" can be transliterated as "the third planet from the sun that has one moon has precisely one moon," thus rendering it as tautological as the germane expressions of basic arithmetic such as "2 + 2 = 4".
Hume wants to prove that certainty
Certainty
Certainty can be defined as either:# perfect knowledge that has total security from error, or# the mental state of being without doubtObjectively defined, certainty is total continuity and validity of all foundational inquiry, to the highest degree of precision. Something is certain only if no...
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
Brain in a vat
In philosophy, the brain in a vat is an element used in a variety of thought experiments intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning...
theory) and other arguments made by philosophical skeptics. It is always logically possible that any given statement about the world is false. (Note that statements like "either the Earth has precisely one moon, or not" are really truths of logic, and say nothing about the world).
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 rock, 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 give us any reason to think that in the future, rocks will fall when in the same circumstances. It would give us reason only if we add as a premise that the future will resemble 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
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...
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
Existence of God
Arguments for and against the existence of God have been proposed by philosophers, theologians, scientists, and others. In philosophical terms, arguments for and against the existence of God involve primarily the sub-disciplines of epistemology and ontology , but also of the theory of value, since...
(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, 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
Ontological argument
The ontological argument for the existence of God is an a priori argument for the existence of God. The ontological argument was first proposed by the eleventh-century monk Anselm of Canterbury, who defined God as the greatest possible being we can conceive...
for the existence of a non-observable (non-material) 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 famously rejected the idea of any meaningful statement that did not fall into this schema, saying:
- If we take in our hand any volume; of divinityDivinityDivinity and divine are broadly applied but loosely defined terms, used variously within different faiths and belief systems — and even by different individuals within a given faith — to refer to some transcendent or transcendental power or deity, or its attributes or manifestations in...
or school metaphysicsMetaphysicsMetaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...
, 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 UnderstandingAn Enquiry Concerning Human UnderstandingAn Enquiry Concerning Human Understanding is a book by the Scottish empiricist philosopher David Hume, published in 1748. It was a revision of an earlier effort, Hume's A Treatise of Human Nature, published anonymously in London in 1739–40...
- - An Enquiry Concerning Human Understanding
-
This same idea has perdured in relatively contemporary schools of philosophy, such as logical positivism
Logical positivism
Logical positivism is a philosophy that combines empiricism—the idea that observational evidence is indispensable for knowledge—with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions of epistemology.It may be considered as a type of analytic...
. This general attitude is strikingly present in Alfred Ayer
Alfred Ayer
Sir Alfred Jules "Freddie" Ayer was a British philosopher known for his promotion of logical positivism, particularly in his books Language, Truth, and Logic and The Problem of Knowledge ....
's logical empiricist work Language, Truth and Logic.
Criticisms
There are two notable objections to Hume's fork. KantImmanuel Kant
Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....
, for example, famously defended the idea of synthetic a priori propositions. W.V.O. Quine also argued against the well-defined distinction between analytic and synthetic propositions required by Hume's fork in his landmark paper Two Dogmas of Empiricism
Two Dogmas of Empiricism
W. V. Quine's paper Two Dogmas of Empiricism, published in 1951, is one of the most celebrated papers of twentieth century philosophy in the analytic tradition. According to Harvard professor of philosophy Peter Godfrey-Smith, this "paper [is] sometimes regarded as the most important in all of...
.