« Ch.IV. Q.20. Moral Certainty | Main | Ch.IV. Q.22. Agnosticism »

July 26, 2005

Ch.IV. Q.21. A Priori and A Posteriori

A PRIORI and a posteriori proof have been employed to prove the existence of God. A priori proof reasons from forms of cognition which are seen to be prior to and independent of experience. A posteriori proof reasons from empirical premises—drawn from experience. Our acquaintance with a priori premises is occasioned by experience; but our assurance of their validity is intuitive and not drawn from experience.

2. Aristotle and the scholastics applied the phrase a priori to reasoning from cause to effect, and the phrase a posteriori to reasoning from effect to cause.1 The definitions here given have prevailed since the time of Kant.2

3. A priori proof is not demonstrative unless both the premises and the deductions made from them are necessary. In Theism this is not the case; for, as has been said already, the being of God is implicitly postulated in every theistic argument. Moreover, the purely a priori nature of theistic arguments called a priori is disputable.

4. A posteriori arguments are most convincing with the majority of men, who find it difficult to follow abstract reasoning or appreciate its force. The value of a priori arguments lies in this, that they show men's belief in God to be grounded in the original constitution of the human mind.3


1 e.g. in St. Thos., Summa, I. ii 2.

2 Fleming, Vocabulary, "A Priori."

3 Cf. Q. xxiv. 4.

Posted by Debra Bullock at July 26, 2005 06:38 PM

Trackback Pings

TrackBack URL for this entry:
http://disseminary.org/mt/mt-tb.cgi/462

Comments