St. Thomas Aquinas: Definition of Law, Reason

ST. THOMAS ADDRESSES the definition of law in Question 90 of his so-called “Treatise on Law” (which is actually part of his Summa Theologica, specifically Questions 90-97 of the first part of the second part of this multi-volume work). St. Thomas first addresses the issue of whether the law is something that is based upon the faculty of practical reason of the law giver, or something else, in particular, the will of the law giver.

Relying principally on the insights in Aristotle’s Physics, St. Thomas concludes that law must principally pertain to reason, and not to the will. He reaches this conclusion because the “rule and measure” of all human acts must be the reason, since reason, and not will, is the proper faculty to direct the end of man. Since law is something that induces man to act, or restrains him from acting, it must accord with the “rule and measure” directing all human acts, which is reason. Ultimately, in St. Thomas's view, it is at the bar of reason to which law is answerable. Naturally, this determination would apply to all law. Thus Eternal Law, the Natural Law, Divine Law, and Human Law would all conform to Reason. Although the Natural Law and Human Law operate under the right reason of man, all manner of law is ultimately subject to conformity with the Divine Reason.

In his handling of the issue, it is apparent that St. Thomas recognizes that the word "law" may be used in an inexact sense. He observes that it is precisely in an imprecise sense that St. Paul uses it when he talks about the “law in my members” in Romans 7:23 to refer to the disposition or tendency toward sin that is referred to as concupiscence. This "law" is not actual law, since it is not based upon reason, but a disordered disposition. Nor is such law actually in the members of a human being, since reason is not be found in the bodily members, but only in the intellect Nevertheless, the term "law" may imprecisely be used to refer to concupiscence because it tugs on us though in a different manner than law, strictly defined, does. Similarly, the "laws of nature," such as scientific "laws," are not strictly laws, but are called laws only in a manner of speaking.

The reason that St. Thomas refers to in his definition of law is what is called the practical reason (ratio practica). This sort of reasoning should be distinguished from the speculative or theoretical reason. The speculative or theoretical reason, entirely intellectual, works by means of argument, applying syllogistic thinking to definitions and propositions to arrive at truths. Speculative or theoretical reason is thus used by humans to determine what is or what one ought to assent to or believe in, that is, what is true, and not what one is supposed to do, that is, to do good and avoid evil.

On the other hand, practical reason is the faculty that man uses to determine what he is supposed to do, and as such it informs us of what is good and what is evil. It relates to one's intent or end (purpose) in acting and is the basis or odering that end. (Some philsophers, such as David Hume, reject the suggestion that practical reason is able to determine what is good and what is evil, and they hold that practical reason is purely instrumental, but that is another issue for another day.)

Because practical reason relates to action, it is a combination of both reason and will. As R. J. Henle puts it: "The act of Practical Reason is a composite one and involves an interplay of will and intellect." R. J. Henle, S.J., ed. The Treatise on Law (Notre Dame: Notre Dame University Press, 1993), [314], 65.

Practical reason similarly uses a syllogistic thinking, applying it to definitions and propositions. But in the practical reason, the “universal propositions of the practical intellect that are directed to actions have the nature of law.” ST IaIIae Q.90, art.1, ad.2. Sometimes, these universal propositions are applied as a result of habit. At other times, these propositions are applied with full awareness and express consideration.

In assessing the interplay of reason and will in the faculty of practical reasoning, St. Thomas insists that reason is preeminent over will. Therefore, law pertains primarily to the reason, and not the will. In taking this position, St. Thomas rejects any implication to the contrary that may have been inferred in the Institutes of the Emperor Justinian. The legal text referred to by St. Thomas defined law in terms of the will of the emperor: Quod principi placuit legis habet vigorem. Inst., I.ii.6. (“Whatsoever pleases the sovereign has the force of law.”) In the Middle Ages, the Institutes and Digest (which with the other laws known as the Novellae) were known as the Corpus Juris Civilis or Codex of the Emperor Justinian. These laws were held in great esteem because of their antiquity and because of the reputation of Justinian as a Christian emperor (the Eastern Church considered him a saint). Justinian's Code, therefore, was to considered to be written reason (ratio scripta), and so was applied to human law as the Scriptures were applied to Divine belief. In his Summa Theologica, St. Thomas Aquinas calls the Emperor Justinian, "the Jurist," like he calls Aristotle, "the Philosopher."

St. Thomas rejects the notion that it is the will which moves us to act; rather, St. Thomas believes that the law is what commands and what forbids, and that this command is properly something pertaining to reason, and it is not something the will engages in except after reason has done its task. While the a person may will a certain end, the reason is what should determine that end, and which issues the command that ordains to that end. Without reason's ordering and guidance, there would be no rule of reason behind that act of will. In St. Thomas’s view, therefore Justinian "the Jurist" must be understood as implying that the will of the sovereign is in accord with some rule of reason. Otherwise, St. Thomas urges, "the sovereign’s will would savor of lawlessness rather than of law." Therefore, St. Thomas concludes, the source of moral obligations, and similarly legal obligations, are based upon a "reasonable will" (rationabile . . . voluntate) or a "will regulated by reason" (voluntate . . . ratione regulata). ST IaIIae, Q. 97, art. 3, resp.

It is apparent that St. Thomas's doctrine would exclude any theory of law that places something other than right reason at the helm of law, whether that something else is the will (even the alleged Divine will), convenience, custom, politics, power, freedom, the genius of the peoples, any idealogy, or anything else. Though these latter factors may have a role to play in fashioning human law, in St. Thomas's view they must always play a subordinate role to rightly-fashioned practical reason. (recta ratio practica).

The French scholar Jean Gerson (1363-1429) is in full compliance with St. Thomas when he states: "Lex est recta ratio practica secundum quam motus et operationes rerum in suos fines ordinatate regulantur." "Law is right practical reason according to which the mode and operations of things are regulated to their final end." Jean Gerson, Oevres Complètes, IX, ed. P. Glorieux (Paris, 1973), p. 134, quoted in Latin in Richard Tuck, Natural Rights Theories: Their Origin and Development (Cambridge: Cambridge University Press, 1981), 27.

In this, Aristotle, Cicero, St. Thomas Aquinas, and Jean Gerson are united. This teaching is our heritage.