A priori and a posteriori
A priori ('from the earlier') and a posteriori ('from the later') are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on experience. A priori knowledge is independent from any experience. Examples include mathematics,[i] tautologies and deduction from pure reason.[ii] A posteriori knowledge depends on empirical evidence. Examples include most fields of science and aspects of personal knowledge.
"A priori" and "A posteriori" redirect here. For other uses, see A priori (disambiguation) and A posteriori (disambiguation).
The terms originate from the analytic methods found in Organon, a collection of works by Aristotle. Prior analytics (a priori) is about deductive logic, which comes from definitions and first principles. Posterior analytics (a posteriori) is about inductive logic, which comes from observational evidence.
Both terms appear in Euclid's Elements and were popularized by Immanuel Kant's Critique of Pure Reason, an influential work in the history of philosophy.[1] Both terms are primarily used as modifiers to the noun knowledge (i.e., a priori knowledge). A priori can be used to modify other nouns such as truth. Philosophers may use apriority, apriorist and aprioricity as nouns referring to the quality of being a priori.[2]
Examples[edit]
A priori[edit]
Consider the proposition: "If 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[edit]
Consider the proposition: "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.
History[edit]
Early uses[edit]
The term a priori is Latin for 'from what comes before' (or, less literally, 'from first principles, before experience'). In contrast, the term a posteriori is Latin for 'from what comes later' (or 'after experience').
They appear in Latin translations of 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's theory of recollection, related in the dialogue Meno, according to which something like a priori knowledge is knowledge inherent, intrinsic in the human mind.
Albert of Saxony, a 14th-century logician, wrote on both a priori and a posteriori.[11]
The early modern Thomistic philosopher John Sergeant differentiates the terms by the direction of inference regarding proper causes and effects. To demonstrate something a priori is to "Demonstrate Proper Effects from Proper Efficient Causes" and likewise to demonstrate a posteriori is to demonstrate "Proper Efficient Causes from Proper Effects", according to his 1696 work The Method to Science Book III, Lesson IV, Section 7.
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".[12] A priori and a posteriori arguments for the existence of God appear in his Monadology (1714).[12]
George Berkeley outlined the distinction in his 1710 work A Treatise Concerning the Principles of Human Knowledge (para. XXI).
Immanuel Kant[edit]
The 18th-century German philosopher Immanuel Kant (1781) advocated a blend of rationalist and empiricist theories. Kant says, "Although all our cognition begins with experience, it does not follow that it arises from [is caused by] experience."[13] 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:[13]