Summa Theologica:
Selected Questions on Law and Justice

Thomas Aquinas (~1225-1274)

Of the Essence of Law

Article 1:
Whether law is something pertaining to reason?

Objection 1. It would seem that law is not something pertaining to reason. For the Apostle says (Rm. 7:23): “I see another law in my members,” etc. But nothing pertaining to reason is in the members; since the reason does not make use of a bodily organ. Therefore law is not something pertaining to reason.

Objection 2. Further, in the reason there is nothing else but power, habit, and act. But law is not the power itself of reason. In like manner, neither is it a habit of reason: because the habits of reason are the intellectual virtues of which we have spoken above (Q57). Nor again is it an act of reason: because then law would cease, when the act of reason ceases, for instance, while we are asleep. Therefore law is nothing pertaining to reason.

Objection 3. Further, the law moves those who are subject to it to act aright. But it belongs properly to the will to move to act, as is evident from what has been said above (Q9:1). Therefore law pertains, not to the reason, but to the will; according to the words of the Jurist: “Whatsoever pleaseth the sovereign, has force of law.”

On the contrary, It belongs to the law to command and to forbid. But it belongs to reason to command, as stated above (Q17:1). Therefore law is something pertaining to reason.

I answer that, Law is a rule and measure of acts, whereby man is induced to act or is restrained from acting: for “lex” [law] is derived from “ligare” [to bind], because it binds one to act. Now the rule and measure of human acts is the reason, which is the first principle of human acts, as is evident from what has been stated above (Q1:1, ad 3); since it belongs to the reason to direct to the end, which is the first principle in all matters of action, according to the Philosopher. Now that which is the principle in any genus, is the rule and measure of that genus: for instance, unity in the genus of numbers, and the first movement in the genus of movements. Consequently it follows that law is something pertaining to reason.

Reply to Objection 1. Since law is a kind of rule and measure, it may be in something in two ways. First, as in that which measures and rules: and since this is proper to reason, it follows that, in this way, law is in the reason alone. Secondly, as in that which is measured and ruled. In this way, law is in all those things that are inclined to something by reason of some law: so that any inclination arising from a law, may be called a law, not essentially but by participation as it were. And thus the inclination of the members to concupiscence is called “the law of the members.”

Reply to Objection 2. Just as, in external action, we may consider the work and the work done, for instance the work of building and the house built; so in the acts of reason, we may consider the act itself of reason, i.e., to understand and to reason, and something produced by this act. With regard to the speculative reason, this is first of all the definition; secondly, the proposition; thirdly, the syllogism or argument. And since also the practical reason makes use of a syllogism in respect of the work to be done, as stated above (Q13:3; Q76:1) and since as the Philosopher teaches; hence we find in the practical reason something that holds the same position in regard to operations, as, in the speculative intellect, the proposition holds in regard to conclusions. Such like universal propositions of the practical intellect that are directed to actions have the nature of law. And these propositions are sometimes under our actual consideration, while sometimes they are retained in the reason by means of a habit.

Reply to Objection 3. Reason has its power of moving from the will, as stated above (Q17:1): for it is due to the fact that one wills the end, that the reason issues its commands as regards things ordained to the end. But in order that the volition of what is commanded may have the nature of law, it needs to be in accord with some rule of reason. And in this sense is to be understood the saying that the will of the sovereign has the force of law; otherwise the sovereign’s will would savor of lawlessness rather than of law.

Article 2:
Whether the law is always something directed to the common good?

Objection 1. It would seem that the law is not always directed to the common good as to its end. For it belongs to law to command and to forbid. But commands are directed to certain individual goods. Therefore the end of the law is not always the common good.

Objection 2. Further, the law directs man in his actions. But human actions are concerned with particular matters. Therefore the law is directed to some particular good.

Objection 3. Further, Isidore says: “If the law is based on reason, whatever is based on reason will be a law.” But reason is the foundation not only of what is ordained to the common good, but also of that which is directed private good. Therefore the law is not only directed to the good of all, but also to the private good of an individual.

On the contrary, Isidore says that “laws are enacted for no private profit, but for the common benefit of the citizens.”

I answer that, As stated above (1), the law belongs to that which is a principle of human acts, because it is their rule and measure. Now as reason is a principle of human acts, so in reason itself there is something which is the principle in respect of all the rest: wherefore to this principle chiefly and mainly law must needs be referred. Now the first principle in practical matters, which are the object of the practical reason, is the last end: and the last end of human life is bliss or happiness, as stated above (Q2:7; Q3:1). Consequently the law must needs regard principally the relationship to happiness. Moreover, since every part is ordained to the whole, as imperfect to perfect; and since one man is a part of the perfect community, the law must needs regard properly the relationship to universal happiness. Wherefore the Philosopher, in the above definition of legal matters mentions both happiness and the body politic: for he says that we call those legal matters “just, which are adapted to produce and preserve happiness and its parts for the body politic”: since the state is a perfect community, as he says in Polit. i, 1.

Now in every genus, that which belongs to it chiefly is the principle of the others, and the others belong to that genus in subordination to that thing: thus fire, which is chief among hot things, is the cause of heat in mixed bodies, and these are said to be hot in so far as they have a share of fire. Consequently, since the law is chiefly ordained to the common good, any other precept in regard to some individual work, must needs be devoid of the nature of a law, save in so far as it regards the common good. Therefore every law is ordained to the common good.

Reply to Objection 1. A command denotes an application of a law to matters regulated by the law. Now the order to the common good, at which the law aims, is applicable to particular ends. And in this way commands are given even concerning particular matters.

Reply to Objection 2. Actions are indeed concerned with particular matters: but those particular matters are referable to the common good, not as to a common genus or species, but as to a common final cause, according as the common good is said to be the common end.

Reply to Objection 3. Just as nothing stands firm with regard to the speculative reason except that which is traced back to the first indemonstrable principles, so nothing stands firm with regard to the practical reason, unless it be directed to the last end which is the common good: and whatever stands to reason in this sense, has the nature of a law.

Article 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 (Q90:2). Now through the eternal law all things are most orderly, as Augustine states. Therefore the natural law suffices for the ordering of all human affairs. Consequently there is no need for a human law.

Objection 2. Further, a law bears the character of a measure, as stated above (Q90:1). 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.

Objection 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 Wisdom 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 distinguishes two kinds of law, the one eternal, the other temporal, which he calls human.

I answer that, As stated above (Q90:1 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 (Q90:1). 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 law, as from general and indemonstrable principles, that the human resaon needs to proceed to the more particular determination of certain matters. These particular determinations, devised by human reason, are called human laws, provided the other essential conditions of law be observed, as stated above (Q90:2-4). Wherefore Tully says in his Rhetoric that justice has its source in nature; thence certain things came into custom by reason of their utility; afterwards these things which emanated from nature and were approved by custom, were sanctioned by fear and reverence for the law.

Reply to Objection 1. The human reason cannot have a full participation of the dictate of the Divine Reason, but according to its own mode, and imperfectly. Consequently, as on the part of the speculative reason, by a natural participation of Divine Wisdom, there is in us the knowledge of certain general principles, but not proper knowledge of each single truth, such as that contained in the Divine Wisdom; so too, on the part of the practical reason, man has a natural participation of the eternal law, according to certain general principles, but not as regards the particular determinations of individual cases, which are, however, contained in the eternal law. Hence the need for human reason to proceed further to sanction them by law.

Reply to Objection 2. Human reason is not, of itself, the rule of things: but the principles impressed on it by nature, are general rules and measures of all things relating to human conduct, whereof the natural reason is the rule and measure, although it is not the measure of things that are from nature.

Reply to Objection 3. The practical reason is concerned with practical matters, which are singular and contingent: but not with necessary things, with which the speculative reason is concerned. Wherefore human laws cannot have that inerrancy that belongs to the demonstrated conclusions of sciences. Nor is it necessary for every measure to be altogether unerring and certain, but according as it is possible in its own particular genus.

Article 4:
Whether promulgation is essential to a law?

Objection 1. It would seem that promulgation is not essential to a law. For the natural law above all has the character of law. But the natural law needs no promulgation. Therefore it is not essential to a law that it be promulgated.

Objection 2. Further, it belongs properly to a law to bind one to do or not to do something. But the obligation of fulfilling a law touches not only those in whose presence it is promulgated, but also others. Therefore promulgation is not essential to a law.

Objection 3. Further, the binding force of a law extends even to the future, since “laws are binding in matters of the future,” as the jurists say. But promulgation concerns those who are present. Therefore it is not essential to a law.

On the contrary, It is laid down in the Decretals, dist. 4, that “laws are established when they are promulgated.”

I answer that, As stated above (1), a law is imposed on others by way of a rule and measure. Now a rule or measure is imposed by being applied to those who are to be ruled and measured by it. Wherefore, in order that a law obtain the binding force which is proper to a law, it must needs be applied to the men who have to be ruled by it. Such application is made by its being notified to them by promulgation. Wherefore promulgation is necessary for the law to obtain its force.

Thus from the four preceding articles, the definition of law may be gathered; and it is nothing else than an ordinance of reason for the common good, made by him who has care of the community, and promulgated.

Reply to Objection 1. The natural law is promulgated by the very fact that God instilled it into man’s mind so as to be known by him naturally.

Reply to Objection 2. Those who are not present when a law is promulgated, are bound to observe the law, in so far as it is notified or can be notified to them by others, after it has been promulgated.

Reply to Objection 3. The promulgation that takes place now, extends to future time by reason of the durability of written characters, by which means it is continually promulgated. Hence Isidore says that “lex [law] is derived from legere [to read] because it is written.”