Reply Obj. 1:  This argument would hold, if the natural law were something different from the eternal law:  whereas it is nothing but a participation thereof, as stated above.

Reply Obj. 2:  Every act of reason and will in us is based on that which is according to nature, as stated above (Q. 10, A. 1):  for every act of reasoning is based on principles that are known naturally, and every act of appetite in respect of the means is derived from the natural appetite in respect of the last end.  Accordingly the first direction of our acts to their end must needs be in virtue of the natural law.

Reply Obj. 3:  Even irrational animals partake in their own way of the Eternal Reason, just as the rational creature does.  But because the rational creature partakes thereof in an intellectual and rational manner, therefore the participation of the eternal law in the rational creature is properly called a law, since a law is something pertaining to reason, as stated above (Q. 90, A. 1).  Irrational creatures, however, do not partake thereof in a rational manner, wherefore there is no participation of the eternal law in them, except by way of similitude. ________________________

THIRD ARTICLE [I-II, Q. 91, Art. 3]

Whether There Is a Human Law?

Objection 1:  It would seem that there is not a human law.  For the natural law is a participation of the eternal law, as stated above (A. 2).  Now through the eternal law “all things are most orderly,” as Augustine states (De Lib.  Arb. i, 6).  Therefore the natural law suffices for the ordering of all human affairs.  Consequently there is no need for a human law.

Obj. 2:  Further, a law bears the character of a measure, as stated above (Q. 90, A. 1).  But human reason is not a measure of things, but vice versa, as stated in Metaph. x, text. 5.  Therefore no law can emanate from human reason.

Obj. 3:  Further, a measure should be most certain, as stated in Metaph. x, text. 3.  But the dictates of human reason in matters of conduct are uncertain, according to Wis. 9:14:  “The thoughts of mortal men are fearful, and our counsels uncertain.”  Therefore no law can emanate from human reason.

On the contrary, Augustine (De Lib.  Arb. i, 6) distinguishes two kinds of law, the one eternal, the other temporal, which he calls human.

I answer that, As stated above (Q. 90, A. 1, ad 2), a law is a dictate of the practical reason.  Now it is to be observed that the same procedure takes place in the practical and in the speculative reason:  for each proceeds from principles to conclusions, as stated above (ibid.).  Accordingly we conclude that just as, in the speculative reason, from naturally known indemonstrable principles, we draw the conclusions of the various sciences, the knowledge of which is not imparted to us by nature, but acquired by the efforts of reason, so too it is from the precepts of the natural