Is law something that belongs to reason?

It seems that law is not something that belongs to reason (non sit aliquid rationis):

Objection 1:  In Romans 7:23 the Apostle says, “I see another law in my members ... .”  But in those members there is nothing that belongs to reason, since reason does not use a corporeal organ.  Therefore, law is not something that belongs to reason.

Objection 2:  Nothing exists in reason which is not either a power, a habit, or an act.  But law is not the very power of reason itself.  Likewise, law is not a habit of reason, since the habits of reason are the intellectual virtues that were discussed above (q. 57).  Nor, again, is law an act of reason, since if it were, then law would cease to exist when reason ceased to act, e.g., in those who are asleep.  Therefore, law is not something that belongs to reason.

Objection 3:  Law moves those who are subject to the law to act in an upright way (recte).  But as is clear from what was said above (q. 9, a. 1), it is properly speaking the role of the will to move one to act.  Therefore, law has to do not with reason but rather with the will, in keeping with what the Legal Expert (iurisperitus) says [in Digestum Vetus 1]:  “Whatever pleases the ruler (princeps) has the force of law.”

But contrary to this:  It is law’s function to command and forbid.  But as was established above (q. 17, a. 1), commanding belongs to reason.  Therefore, law is something that belongs to reason.

I respond:  Law is a certain rule and measure of acts in accord with which one is either induced to act or restrained from acting.  For ‘law’ (lex) is derived from ‘to bind’ (ligare), since law obligates (obligare) one to act.  Now the rule and measure of human acts is reason, which, as is clear from what was said above (q. 1, a. 1), is the first principle of human acts.  For it belongs to reason to order things to their endCwhere, according to the Philosopher, the end is the first principle in the case of things to be done (agenda).  But in every genus, that which is the principle is the measure and rule of that genus.  For instance, one is the measure in the genus number, and the first movement is the measure in the genus movement.  Hence, it follows that law is something that belongs to reason.

Reply to objection 1:  Since law is a rule and measure, there are two ways in which it is said to exist in something.
First, law exists in that which measures and regulates.  And since this is proper to reason, law taken in this sense exists in reason alone.
Second, law exists in that which is regulated and measured.  And this is how law exists in all the things that are inclined in any way by any kind of law.  As a result, any inclination that stems from any kind of law can itself be called a law—not by its essence but, as it were, by participation.  And it is in this sense that the very inclination of the members [of the body] toward sensual desire is called ‘the law of the members’.

Reply to objection 2:  Just as in the case of exterior acts one must consider both the operation (operatio) and the thing that is done (operatum)— e.g., the act of building and the thing built—so too in the works of reason one must consider (a) the very acts of reason, i.e., the act of understanding and the act of discursive reasoning, and (b) what is constituted by acts of this sort.  In the case of speculative reason, the constituted things are, first, the definition; second, the proposition (enunciatio); and, third, the syllogism or argument.
Now, as was explained above (q. 76, a. 1) in keeping with what the Philosopher teaches in Ethics 7, practical reason likewise uses a certain type of syllogism with respect to things that can be done (operabilia).  Hence, in the case of practical reason there is something that is related to the actions (operationes) in the same way that the proposition is related to the conclusions in the case of speculative reason. These universal propositions of practical reason, which are ordered toward actions, have the character of law.  At certain times these propositions are actually being considered, and at other times reason possesses them as habits.

Reply to objection 3:  As was explained above (q. 17, a. 1), it is from the will that reason has its power to move.  For it is because someone wills the end that his reason issues commands regarding what is ordered toward the end.  However, for an act of will about what is commanded to have the character of law, it must be regulated in some way by reason (aliqua ratione regulata).  And this is how to understand the claim that the ruler’s will has the force of law; otherwise, the ruler’s will would constitute wickedness (iniquitas) rather than law.