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''A priori'' and ''a posteriori'' ('from the earlier' and 'from the later', respectively) are Latin phrases used in
philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about Metaphysics, existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, language. Such questio ...

philosophy
to distinguish types of
knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to e ...
, justification, or
argument In logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, la ...
by their reliance on empirical evidence or experience. ''A priori'' knowledge is that which is independent from
experience Experience refers to conscious , an English Paracelsian Paracelsianism (also Paracelsism; German: ') was an early modern History of medicine, medical movement based on the theories and therapies of Paracelsus. It developed in the second half ...

experience
. Examples include
mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and their changes (cal ...
,Some
associationist Associationism is the idea that mental processes operate by the association of one mental state with its successor states. It holds that all mental processes are made up of discrete psychological elements and their combinations, which are believed ...
philosophers have contended that mathematics comes from experience and is not a form of any a priori knowledge ()
tautologies, and deduction from
pure reason Speculative reason, sometimes called theoretical reason or pure reason, is theoretical (or logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, label=none, lit=possessed of reason, intellectual, dialectical, argument ...
.
Galen Strawson Galen John Strawson (born 1952) is a British analytic philosopher and literary critic who works primarily on philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind and its relations ...
has stated that an ''a priori'' argument is one in which "you can see that it is
true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherw ...

true
just lying on your couch. You don't have to get up off your couch and go outside and examine the way things are in the physical world. You don't have to do any science." ()
''A posteriori'' knowledge is that which depends on
empirical evidence Empirical evidence for a proposition In logic and linguistics, a proposition is the meaning of a declarative sentence (linguistics), sentence. In philosophy, "Meaning (philosophy), meaning" is understood to be a non-linguistic entity which is s ...
. Examples include most fields of
science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of ...

science
and aspects of personal knowledge. Both terms appear in
Euclid Euclid (; grc-gre, Εὐκλείδης Euclid (; grc, Εὐκλείδης – ''Eukleídēs'', ; fl. 300 BC), sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referre ...

Euclid
's '' Elements'' but were popularized by
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
's ''
Critique of Pure Reason ''Critique of Pure Reason'' (german: Kritik der reinen Vernunft; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant Immanuel Kant (, ; ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher a ...
'', one of the most influential works in the
history of philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about existence Existence is the ability of an entity to interact with physical reality Reality is the sum or aggregate of all that is real or existen ...
. Both terms are primarily used as modifiers to the
noun A noun () is a word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), meaning. In many l ...

noun
"knowledge" (i.e. "''a priori'' knowledge"). ''A priori'' can also be used to modify other nouns such as 'truth". Philosophers also may use ''apriority'', ''apriorist'', and ''aprioricity'' as nouns referring to the quality of being ''a priori''.


Examples

The intuitive distinction between ''a priori'' and ''a posteriori'' knowledge (or justification) is best seen via examples, as below:


''A priori''

Consider the
proposition In logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, lab ...
: "If
George V George V (George Frederick Ernest Albert; 3 June 1865 – 20 January 1936) was King of the United Kingdom and the British Dominions, and Emperor of India, from 6 May 1910 until his death in 1936. Born during the reign of his grandmother ...

George V
reigned at least four days, then he reigned more than three days." This is something that one knows ''a priori'', because it expresses a statement that one ''can'' derive by reason alone.


''A posteriori''

Compare the above with the proposition expressed by the sentence: "George V reigned from 1910 to 1936." This is something that (if true) one must come to know ''a posteriori'', because it expresses an empirical fact unknowable by reason alone.


Aprioricity, analyticity, and necessity


Relation to the analytic-synthetic

Several philosophers, in reaction to
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
, sought to explain ''a priori'' knowledge without appealing to, as
Paul Boghossian Paul Artin Boghossian (; born 1957) is an American philosopher. He is Silver Professor of Philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemolog ...
explains, "a special faculty…that has never been described in satisfactory terms." One theory, popular among the
logical positivists Logical positivism, later called logical empiricism, and both of which together are also known as neopositivism, was a movement in Western philosophy Western philosophy refers to the philosophy, philosophical thought and work of the Western worl ...
of the early 20th century, is what Boghossian calls the "analytic explanation of the a priori." The distinction between analytic and synthetic propositions was first introduced by Kant. While his original distinction was primarily drawn in terms of conceptual containment, the contemporary version of such distinction primarily involves, as American philosopher W. V. O. Quine put it, the notions of "true by virtue of meanings and independently of fact." Analytic propositions are thought to be true in virtue of their meaning alone, while ''a posteriori'' propositions are thought to be true in virtue of their meaning ''and'' of certain facts about the world. According to the analytic explanation of the ''a priori'', all ''a priori'' knowledge is analytic; so ''a priori'' knowledge need not require a special faculty of pure
intuition Intuition is the ability to acquire knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is something that is truth, true. The usual test for a statement of fact is verifiability—that is ...

intuition
, since it can be accounted for simply by one's ability to understand the meaning of the proposition in question. More simply, proponents of this explanation claimed to have reduced a dubious
metaphysical Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between ...

metaphysical
faculty of pure reason to a legitimate linguistic notion of analyticity. The analytic explanation of ''a priori'' knowledge has undergone several criticisms. Most notably, Quine argues that the analytic–synthetic distinction is illegitimate:
But for all its a priori reasonableness, a boundary between analytic and synthetic statements simply has not been drawn. That there is such a distinction to be drawn at all is an unempirical dogma of empiricists, a metaphysical article of faith.
While the soundness of Quine's critique is highly disputed, it had a powerful effect on the project of explaining the ''a priori'' in terms of the analytic.


Relation to the necessary truths and contingent truths

The metaphysical distinction between ''necessary'' and ''contingent'' truths has also been related to ''a priori'' and ''a posteriori'' knowledge. A proposition that is necessarily true is one in which its negation is self-contradictory. Thus, it is said to be true in every
possible world A possible world is a complete and consistent way the world is or could have been. They are widely used as a formal device in logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously ...
. For example, considering the proposition "all bachelors are unmarried:" its negation (i.e. the proposition that some bachelors are married) is incoherent due to the concept of being unmarried (or the meaning of the word "unmarried") being tied to part of the concept of being a bachelor (or part of the definition of the word "bachelor"). To the extent that contradictions are impossible, self-contradictory propositions are necessarily false as it is impossible for them to be true. The negation of a self-contradictory proposition is, therefore, supposed to be necessarily true. By contrast, a proposition that is contingently true is one in which its negation is not self-contradictory. Thus, it is said ''not'' to be true in every possible world. As Jason Baehr suggests, it seems plausible that all necessary propositions are known ''a priori'', because " nse experience can tell us only about the actual world and hence about what is the case; it can say nothing about what must or must not be the case." Following Kant, some philosophers have considered the relationship between ''aprioricity'', ''analyticity'', and ''necessity'' to be extremely close. According to
Jerry Fodor Jerry Alan Fodor (; April 22, 1935 – November 29, 2017) was an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of Ameri ...

Jerry Fodor
, "
positivism Positivism is a philosophical theory A philosophical theory or philosophical position''Dictionary of Theories'', Jennifer Bothamley is a view that attempts to explain or account for a particular problem in philosophy Philosophy (from ...
, in particular, took it for granted that ''a priori'' truths must be necessary." However, since Kant, the distinction between analytic and synthetic propositions has slightly changed. Analytic propositions were largely taken to be "true by virtue of meanings and independently of fact," while synthetic propositions were not—one must conduct some sort of empirical investigation, looking to the world, to determine the truth-value of synthetic propositions.


Aprioricity, analyticity and necessity

Aprioricity, analyticity, and necessity have since been more clearly separated from each other. American philosopher
Saul Kripke Saul Aaron Kripke (; born November 13, 1940) is an American philosopher American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States ** Americans, citizens and nationa ...

Saul Kripke
(1972), for example, provides strong arguments against this position, whereby he contends that there are necessary ''a posteriori'' truths. For example, the proposition that water is H2O (if it is true): According to Kripke, this statement is both ''necessarily true'', because water and H2O are the same thing, they are identical in every possible world, and truths of identity are logically necessary; and ''a posteriori'', because it is known only through empirical investigation. Following such considerations of Kripke and others (see
Hilary Putnam Hilary Whitehall Putnam (; July 31, 1926 – March 13, 2016) was an American philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'love ...

Hilary Putnam
), philosophers tend to distinguish the notion of aprioricity more clearly from that of necessity and analyticity. Kripke's definitions of these terms, however, diverge in subtle ways from those of Kant. Taking these differences into account, Kripke's controversial analysis of naming as contingent and ''a priori'' would, according to Stephen Palmquist, best fit into Kant's epistemological framework by calling it "analytic a posteriori."In this pair of articles, Stephen Palmquist demonstrates that the context often determines how a particular proposition should be classified. A proposition that is synthetic ''a posteriori'' in one context might be analytic ''a priori'' in another. ()
Aaron Sloman Aaron Sloman is a philosopher and researcher on artificial intelligence Artificial intelligence (AI) is intelligence demonstrated by machines, unlike the natural intelligence human intelligence, displayed by humans and animal cognition, ani ...
presented a brief defence of Kant's three distinctions (analytic/synthetic, apriori/empirical, and necessary/contingent), in that it did not assume "possible world semantics" for the third distinction, merely that some part of ''this'' world might have been different. The relationship between aprioricity, necessity, and analyticity is not found to be easy to discern. However, most philosophers at least seem to agree that while the various distinctions may overlap, the notions are clearly not identical: the ''a priori''/''a posteriori'' distinction is
epistemological Epistemology (; ) is the Outline of philosophy, branch of philosophy concerned with knowledge. Epistemologists study the nature, origin, and scope of knowledge, epistemic Justification (epistemology), justification, the Reason, rationality o ...

epistemological
; the analytic/synthetic distinction is
linguistic Linguistics is the scientific study of language A language is a structured system of communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo ...

linguistic
,; and the necessary/contingent distinction is
metaphysical Metaphysics is the branch of philosophy that studies the first principles of being, identity and change, space and time, causality, necessity and possibility. It includes questions about the nature of consciousness and the relationship between ...

metaphysical
., §2-3


History


Early uses

The term ''a priori'' is
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
for 'from what comes before' (or, less literally, 'from first principles, before experience'). In contrast, the term ''a posteriori'' is
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
for 'from what comes later' (or 'after experience'). They appear in Latin translations of
Euclid Euclid (; grc-gre, Εὐκλείδης Euclid (; grc, Εὐκλείδης – ''Eukleídēs'', ; fl. 300 BC), sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referre ...

Euclid
's '' Elements'', a work widely considered during the early European modern period as the model for precise thinking. An early philosophical use of what might be considered a notion of ''a priori'' knowledge (though not called by that name) is
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thought and the Platoni ...

Plato
's ''theory of recollection'', related in the dialogue ''
Meno ''Meno'' (; grc-gre, wikt:Μένων, Μένων, ''Ménōn'') is a Socratic dialogue by Plato. Meno begins the dialogue by asking Socrates whether virtue is taught, acquired by practice, or comes by nature. In order to determine whether virt ...

Meno
'', according to which something like ''a priori'' knowledge is knowledge inherent,
intrinsic In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
in the human mind.
Albert of Saxony en, Frederick Augustus Albert Anthony Ferdinand Joseph Charles Maria Baptist Nepomuk William Xavier George Fidelis , image = Albert of Saxony by Nicola Perscheid c1900.jpg , image_size = , caption = Albert of Saxony by Nicola P ...
, a 14th-century logician, wrote on both ''a priori'' and ''a posteriori''. G. W. Leibniz introduced a distinction between ''a priori'' and ''a posteriori'' criteria for the possibility of a notion in his (1684) short treatise "Meditations on Knowledge, Truth, and Ideas". ''A priori'' and ''a posteriori'' arguments for the existence of God appear in his ''
Monadology The ''Monadology'' (french: La Monadologie, 1714) is one of Gottfried Leibniz's best known works of his later philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, ex ...
'' (1714).
George Berkeley George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley (Bishop of Cloyne The Bishop of Cloyne is an episcopal title that takes its name after the small town of Cloyne in County Cork, Republic of Ireland Irela ...

George Berkeley
outlined the distinction in his 1710 work ''
A Treatise Concerning the Principles of Human Knowledge 160px, First edition of the book ''A Treatise Concerning the Principles of Human Knowledge'' (commonly called ''Treatise'') is a 1710 work, in English, by Irish Empiricist philosopher George Berkeley George Berkeley (; 12 March 168514 Januar ...
'' (para. XXI).


Immanuel Kant

The 18th-century German philosopher
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about r ...

Immanuel Kant
(1781) advocated a blend of rationalist and
empiricist In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...
theories. Kant says, "Although all our cognition begins with experience, it does not follow that it arises from s caused byexperience." According to Kant, ''a priori'' cognition is transcendental, or based on the ''form'' of all possible experience, while ''a posteriori'' cognition is empirical, based on the ''content'' of experience:
It is quite possible that our empirical knowledge is a compound of that which we receive through impressions, and that which the faculty of cognition supplies from itself sensuous impressions ense datagiving merely the ''occasion'' pportunity for a cause to produce its effect
Contrary to contemporary usages of the term, Kant believes that ''a priori'' knowledge is not entirely independent of the content of experience. Unlike the
rationalists In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...
, Kant thinks that ''a priori'' cognition, in its pure form, that is without the admixture of any empirical content, is limited to the deduction of the conditions of possible experience. These ''a priori'', or transcendental conditions, are seated in one's cognitive faculties, and are not provided by experience in general or any experience in particular (although an argument exists that ''a priori'' intuitions can be "triggered" by experience). Kant nominated and explored the possibility of a
transcendental logic ''Critique of Pure Reason'' (german: Kritik der reinen Vernunft; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant Immanuel Kant (, ; ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher a ...
with which to consider the deduction of the ''a priori'' in its pure form.
Space Space is the boundless three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called parameter A parameter (from the Ancient Greek language, Ancient Gre ...

Space
,
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...

time
and
causality Causality (also referred to as causation, or cause and effect) is influence by which one Event (relativity), event, process, state or object (a ''cause'') contributes to the production of another event, process, state or object (an ''effect'') ...
are considered pure ''a priori'' intuitions. Kant reasoned that the pure ''a priori'' intuitions are established via his
transcendental aesthetic ''Critique of Pure Reason'' (german: Kritik der reinen Vernunft; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant Immanuel Kant (, ; ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher a ...
and transcendental logic. He claimed that the human subject would not have the kind of experience that it has were these ''a priori'' forms not in some way constitutive of him as a human subject. For instance, a person would not experience the world as an orderly, rule-governed place unless time, space and causality were determinant functions in the form of perceptual faculties, i. e., there can be no experience in general without space, time or causality as particular determinants thereon. The claim is more formally known as Kant's transcendental deduction and it is the central argument of his major work, the ''
Critique of Pure Reason ''Critique of Pure Reason'' (german: Kritik der reinen Vernunft; 1781; second edition 1787) is a book by the German philosopher Immanuel Kant Immanuel Kant (, ; ; 22 April 1724 – 12 February 1804) was a German Philosophy, philosopher a ...
''. The transcendental deduction argues that time, space and causality are ideal as much as real. In consideration of a possible logic of the ''a priori'', this most famous of Kant's deductions has made the successful attempt in the case for the fact of
subjectivity Subjectivity in a philosophical Philosophy (from , ) is the study of general and fundamental questions, such as those about existence Existence is the ability of an entity to interact with physical or mental reality Reality is the sum ...
, what constitutes subjectivity and what relation it holds with objectivity and the empirical.


Johann Fichte

After Kant's death, a number of philosophers saw themselves as correcting and expanding his philosophy, leading to the various forms of
German Idealism German idealism was a philosophical movement A philosophical movement refers to the phenomenon defined by a group of philosophers A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fund ...
. One of these philosophers was
Johann Fichte Johann Gottlieb Fichte (; ; 19 May 1762 – 29 January 1814) was a German philosopher A philosopher is someone who practices philosophy. The term ''philosopher'' comes from the grc, φιλόσοφος, , translit=philosophos, meaning 'lover ...
. His student (and critic),
Arthur Schopenhauer Arthur Schopenhauer (; ; 22 February 1788 – 21 September 1860) was a German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citize ...
, accused him of rejecting the distinction between ''a priori'' and ''a posteriori'' knowledge:


See also

*
A priori probability An ''a priori'' probability is a probability that is derived purely by deductive reasoning. One way of deriving ''a priori'' probabilities is the principle of indifference, which has the character of saying that, if there are ''N'' mutually exclusi ...
*
Abductive reasoning Abductive reasoning (also called abduction,For example: abductive inference, or retroduction) is a form of logical inference Inferences are steps in reasoning, moving from premises to logical consequences; etymologically, the word ''wikt:inf ...
*
Deductive reasoning Deductive reasoning, also deductive logic, is the process of reasoning Reason is the capacity of consciously applying logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making ...
*
Inductive reasoning Inductive reasoning is a method of reasoning Reason is the capacity of Consciousness, consciously making sense of things, applying logic, and adapting or justifying practices, institutions, and beliefs based on new or existing information. It ...
* Relativized a priori *
Tabula rasa ''Tabula rasa'' (; "blank slate") is the theory that individuals are born without built-in mental content The mind is the set of faculties responsible for mental phenomena A phenomenon (; plural phenomena) is an observable fact or ev ...
* Transcendental empiricism *
Transcendental hermeneutic phenomenology Phenomenology (from Ancient Greek, Greek ''phainómenon'' "that which appears" and ''lógos'' "study") is the Philosophy, philosophical study of the structures of experience and consciousness. As a philosophical movement it was founded in the ea ...
* Transcendental nominalism


References


Notes


Citations


Sources

* * * * * * * * * * * * *


Further reading

* * * . * * * * * * * * * *


External links

* * * *
A priori / a posteriori
— in the Philosophical Dictionary online.
"Rationalism vs. Empiricism"
— an article by Peter Markie in the ''Stanford Encyclopedia of Philosophy''. {{DEFAULTSORT:A Priori and a Posteriori Concepts in epistemology Conceptual distinctions Critical thinking Critical thinking skills Empiricism Justification (epistemology) Kantianism Latin logical phrases Latin philosophical phrases Mental processes Philosophical logic Philosophical theories Philosophy of logic Philosophy of mind Rationalism Reality Sources of knowledge Subjective experience Term logic Thought