Aquinas’ Natural Law

Aquinas’ Natural Law

This extract is from Aquinas’ Summa Theologica and outlines his concept of Natural Law. Key information has been highlighted in bold. There are explanatory notes below.

‘Of the Natural Law. Q 94 Article 2’

Whether the natural law contains several precepts, or only one?

Objection 1: It would seem that the natural law contains, not several precepts, but one only. For law is a kind of precept, as stated above (Q[92], A[2]). If therefore there were many precepts of the natural law, it would follow that there are also many natural laws.

Objection 2: Further, the natural law is consequent to human nature. But human nature, as a whole, is one; though, as to its parts, it is manifold. Therefore, either there is but one precept of the law of nature, on account of the unity of nature as a whole; or there are many, by reason of the number of parts of human nature. The result would be that even things relating to the inclination of the concupiscible faculty belong to the natural law.

Objection 3: Further, law is something pertaining to reason, as stated above (Q[90], A[1]). Now reason is but one in man. Therefore there is only one precept of the natural law.

On the contrary, the precepts of the natural law in man stand in relation to practical matters, as the first principles to matters of demonstration. But there are several first indemonstrable principles. Therefore there are also several precepts of the natural law.

I answer that, as stated above (Q[91], A[3]), the precepts of the natural law are to the practical reason, what the first principles of demonstrations are to the speculative reason; because both are self-evident principles. Now a thing is said to be self-evident in two ways: first, in itself; secondly, in relation to us. Any proposition is said to be self-evident in itself, if its predicate is contained in the notion of the subject: although, to one who knows not the definition of the subject, it happens that such a proposition is not self-evident. For instance, this proposition, ‘Man is a rational being’, is, in its very nature, self-evident, since who says ‘man’, says ‘a rational being’: and yet to one who knows not what a man is, this proposition is not self-evident. Hence it is that, as Boethius says (De Hebdom.), certain axioms or propositions are universally self-evident to all; and such are those propositions whose terms are known to all, as, ‘Every whole is greater than its part’, and, ‘Things equal to one and the same are equal to one another’. But some propositions are self-evident only to the wise, who understand the meaning of the terms of such propositions: thus to one who understands that an angel is not a body, it is self-evident that an angel is not circumscriptively in a place: but this is not evident to the unlearned, for they cannot grasp it.

Now a certain order is to be found in…