A priori and a posteriori  

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A priori from Wiktionary:

  1. Known ahead of time.
  2. Based on hypothesis rather than experiment.
  3. Self-evident, intuitively obvious

"In the well-known passage in the Preface to the Second Edition of the Critick of Pure Reason Kant states the fundamental principle of his method. " It has hitherto been assumed," says he, " that our cognition must conform to the objects, but all attempts to extend our knowledge concerning them a priori by means of concepts have under this assumption failed. Let us try if we may not be more successful in the problems of metaphysics if we assume that the objects must conform to our cognition." In this passage is contained the germ not merely of Kant's philosophy but also of that of Fichte, Schelling and Hegel. Cognition can have a priori knowledge of the object because it is in itself to that extent the object which it knows."--"Going Back to Kant () by George Stokes[1]

Related e



Kunstformen der Natur (1904) by Ernst Haeckel
Kunstformen der Natur (1904) by Ernst Haeckel

A priori and a posteriori ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. A priori knowledge is that which is independent from experience. Examples include mathematics, tautologies, and deduction from pure reason. Galen Strawson has stated that an a priori argument is one in which "you can see that it is 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. Examples include most fields of science and aspects of personal knowledge.

Both terms appear in Euclid's Elements but were popularized by Immanuel Kant's Critique of Pure Reason, one of the most influential works in the history of philosophy. Both terms are primarily used as modifiers to the 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.



Early uses



13th century philosopher Thomas Aquinas, in the Summa Theologica, writes: "Demonstration can be made in two ways: One is through the cause, and is called "a priori," and this is to argue from what is prior absolutely. The other is through the effect, and is called a demonstration "a posteriori"; this is to argue from what is prior relatively only to us. When an effect is better known to us than its cause, from the effect we proceed to the knowledge of the cause. And from every effect the existence of its proper cause can be demonstrated, so long as its effects are better known to us; because since every effect depends upon its cause, if the effect exists, the cause must pre-exist."

Albert of Saxony, a 14th century logician wrote on the both a priori and a posteriori. George Berkeley, the Irish divine and philosopher outlined the distinction in A Treatise Concerning the Principles of Human Knowledge of 1710, though the terms were already well known by that time.

Immanuel Kant


Johann Fichte



See also

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