DEMONSTRATION AND SELF-EVIDENCE 15 



the subject is understood in its definition the identity of subject 

 and predicate is grasped, and the intellect is moved to commit 

 itself irrevocably to the truth of the proposition. If a proposi- 

 tion has a predicate within the definition of its subject, but 

 this subject defies definition by any man, then this proposition 

 can be described as self-evident in itself, but not self-evident 

 to us. If, on the other hand, its subject can be defined by us, 

 it is self-evident both in itself and to us. If the subject is able 

 to be defined only by those who are habituated to operate 

 within a given scientific field, the proposition is said to be self- 

 evident only to the learned. But if is is a common concept 

 understood by every one, it is, of course, self-evident to all. 

 Thus, it is rather easy to see, at least apropos of the prime 

 type of self-evident proposition, the rationale of the traditional 

 division of the "per se nota proposition into the 'per se nota in 

 se and the per se nota quoad nos, and the subdivision of the 

 latter into the per se nota quoad sapientes and the per se nota 

 quoad omnes.-° 



St. Thomas appeals to the fact that the proposition God is 

 is not self-evident quoad nos even though it is self-evident in 

 itself."^ Were we to know the essence of God we could not — 

 nor would we need to — demonstrate His existence, for His 

 essence is His existence. Yet, since we do not know His essence 

 we are able from His effects, which are known to us, to 

 prove His existence. Aristotle and St. Thomas supply several 

 examples of per se nota propositions which are known to all 

 because their terms are common conceptions easily and surely 

 grasped by all men. These examples include: The sanfie thing 

 cannot he and not he; The same proposition does not admit 

 simultaneously of affirmation and denial; The whole is greater 

 than any of its parts; Things equal to one and the same thing 

 are equal to one another; Equals taken away from equals leave 



^° This traditional division of the self-evident proposition is explained by St. 

 Thomas in several texts, including: De Ver., q. 10, a. 12; In IV Met., lect. 5, n. 595; 

 In I Post. Anal., lect. 5, nn. 6-7; In Boeth. de Hebd., lect. 1. Cf., also Cajetan, 

 op. cit., Ch. 3. 



*^ Summa, I, q. 2, a. 1; De Ver., q. 10, a. 12. 



