A priori , Latin phrase, was initially used to indicate a reasoning which goes from the cause to the effect. This direction meets with the Moyen-âge, at Descartes and still at Leibniz; for example, a proof a priori of the existence of God is a proof which leaves what is first by nature ( will natura ). Nevertheless, Leibniz also already employs it in its other direction which is most current.

Generally, indeed, the phrase a priori indicates the knowledge supposed by the experiment, and which cannot be reduced to it.

The concept da priori with the Kantian direction indicates what is thought like necessary and Universel and which, for this reason, can be conceived “independently/independent of the experiment”. A knowledge is a priori if it can be proven without reference none to the experiment. For example, the space and the Temps are forms inherent in the Sujet. According to Kant, space and time cannot exist without the subject. They are what the subject brings to the Connaissance.

Francization

The phrase is francized and is written then “a priori”. This " francization" who is largely discussed (cf http://www.langue-fr.net/index/A/a-priori.htm#complements-dictionnaires) hardly has however direction because the Latin preposition “ab”, elided here of “has”, has nothing to do with the French preposition “with”.

See too

• Synthetic a priori

Zh-yue: 先驗

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