"The primary precepts of the law of nature stand to the practical reason as the first principles of scientific demonstration do to the speculative reason: for both sets of principles are self-evident. A thing is said to be self-evident in two ways, either _in itself_, or _in reference to us. _In itself_ every proposition, the predicate of which can be got from consideration of the subject is said to be self-evident. But it happens that to one who is ignorant of the definition of the subject, such a proposition will not be self-evident: as this proposition, _Man is a rational being_, is self-evident in its own nature, because to name man is to name something rational; and yet, to one ignorant what man is, this proposition is not self-evident. And hence it is that, as Boethius says: "there are some axioms self-evident to all alike." Of this nature are all those propositions whose terms are known to all, as, _Every whole is greater than its part_; and, _Things which are equal to the same thing are equal to one another_. Some propositions again are self-evident only to the wise, who understand the meaning of the terms: as, to one who understands that an angel is not a body, it is self-evident that an angel is not in a place by way of circumscription; [Footnote 11] which is not manifest to others, who do not understand the term." (St. Thos., 1a 2æ q. 94, art. 2, in corp.) [Footnote 11: _Circumscriptive_, which word is explained by St. Thos., 1a, q. 52. art. 1.] One more extract. "From the very nature of an intellectual soul it is proper to man that, as soon as he knows what a whole is, and what a part is, he knows that every whole is greater than its part; and so of the rest. But what is a whole, and what a part, that he cannot know except through sensory impressions. And therefore Aristotle shows that the knowledge of principles comes to us through the senses." (St. Thos., 1a 2æ, q. 51, art. 1, in corp.)