Early uses 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. 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 short treatise "Meditations on Knowledge, Truth, and Ideas" (1684).
A priori and
a posteriori arguments for the existence of God appear in his
Monadology (1714).
George Berkeley outlined the distinction in his 1710 work
A Treatise Concerning the Principles of Human Knowledge (para. XXI).
Immanuel Kant 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." 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 [sense data] giving merely the
occasion [opportunity 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, 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 with which to consider the deduction of the
a priori in its pure form.
Space,
time and
causality are considered pure
a priori intuitions. Kant reasoned that the pure
a priori intuitions are established via his
transcendental aesthetic 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. 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, 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. One of these philosophers was
Johann Fichte. His student (and critic),
Arthur Schopenhauer, accused him of rejecting the distinction between
a priori and
a posteriori knowledge: ==See also==