DEMONSTRATION AND SELF-EVIDENCE 13 



Thomas says that it is 'per se notuvi that nature exists because 

 natural things are manifest to the sense /"^ Natural things exist 

 is an immediate proposition. But it is not self-evident — for, 

 since natural things are existentially contingent and need not 

 be, we cannot assent to the proposition Natural things exist 

 simply because we understand the meaning of its terms. It is 

 immediately evident only on the basis of the empirical fact 

 unmistakably given in our sensory-intellectual grasp of the exis- 

 tence of sensible existents immediately present to the external 

 sense. This is clearly a factually evident proposition. It is of 

 significant relevance for the philosophy of nature, but it is not 

 relevant in the way in which a self-evident proposition is 

 relevant,^^ despite the fact that St. Thomas describes it as per 

 se nota. One more clarification at this point. The immediacy 

 of the self-evident proposition makes it indemonstrable. But 

 not all indemonstrable propositions are immediate (consider 

 conclusions of dialectical or probable argumentation) . Nor 

 even, of course, are all immediate and indemonstrable proposi- 



is greater than its parts can be taken as a proposition which intends simply a 

 report on a concrete situation. As such this is factually evident, and it is not the 

 same as the proposition Every whole is such that it must be greater than any of 

 its parts. This second proposition is, of course, self-evident, and it is certainly 

 known by anyone who can express the former proposition (because the terms which 

 must be known in order that the former be expressed immediately make evident the 

 latter) . Although the most perfect instance of propter quid demonstration involves 

 two premises each of which is self-evident, there is no reason why less strict 

 demonstration cannot include one factually evident premise. The necessity needed 

 in the antecedent of a demonstration would be lacking if every premise were 

 factually evident, but it can be supplied by one self-evident proposition coupled 

 with a factually evident premise. As a matter of fact, demonstration makes sense 

 only in reference to scientific subjects known to exist. "Where both premises are 

 self-evident it is a requirement that the existence of the scientific subject be known 

 prior to demonstration and presumed within demonstration. The existence of the 

 scientific subject can be expressed within a demonstration when one of its premises 

 is factually evident, 



^* Cf., supra, note 11. 



^^ There would be no reason for a philosophy of nature if natural things did not 

 exist; but since they need not exist, the proposition which reports on the fact of 

 their existence cannot be used as a necessary premise manifesting the scientific 

 necessity of any conclusion. 



