Saint Thomas Aquinas    Selections on Ethics

[These selections, chosen by K. Henley, are from various Questions in the First Part of the Second Part of the Summa Theologica. They have been very severely edited, removing the format of objections and responses. Each numbered selection is followed by the citation to Question and Article, and a page reference to the widely available Anton C. Pegis, ed., Basic Writings of Saint Thomas Aquinas (New York: Random House, 1945). The translation is that of the English Dominican Fathers, with minor revisions by Pegis. Material in square brackets is due to K. Henley.]

A. Nature, Reason, and the Virtues

1. Now the virtue of a thing consists in its being well disposed in a manner befitting its nature....But it must be observed that the nature of a thing is chiefly the form from which that thing derives its species [specific natural kind distinguishing it from other natural kinds]. Now man derives his species from his rational soul, and consequently whatever is contrary to the order of reason is, properly speaking, contrary to the nature of man, as man; while whatever is in accord with reason is in accord with the nature of man, as man....Therefore human virtue, which makes a man good, is in accord with man's nature in so far as it accords with his reason; while vice is contrary to man's nature in so far as it is contrary to the order of reason....There is a twofold nature in man, rational and sensitive [sensations, feelings, emotions, desirings, passions, sensory appetites]....Now the presence of vices and sins in man is owing to the fact that he follows the inclination of his sensitive nature against the order of his reason.

Summa Theologica, I-II, Q. 71, Art. 2, in Basic Writings of Saint Thomas Aquinas, ed. Anton C. Pegis (New York: Random House, 1945), vol. 2, pp. 561-562.

2. Human virtue is a habit perfecting man for the purpose of acting well. Now in man there are but two principles of human actions, viz., the intellect or reason and the appetite....Consequently every human virtue must needs be a perfection of one of these principles. Accordingly, if it perfects man's speculative or practical intellect in order that his action may be good, it will be an intellectual virtue; whereas if it perfects his appetite, it will be a moral virtue....Prudence [practical wisdom] is essentially an intellectual virtue. But considered on the part of its matter, it has something in common with the moral virtues, for it is right reason about things to be done....It is in this sense that it is reckoned with the moral virtues.

S. Th., I-II, Q. 58, Art. 3 (Pegis, p. 444)

3. Now in order that a choice be good, two things are required. First, that the intention be directed to a due end; and this is done by moral virtue, which inclines the appetitive power to the good that is in accord with reason, which is a due end. Secondly, that man choose rightly those things which are means to the end; and this he cannot do unless his reason counsel, judge and command rightly, which is the function of prudence [practical reason] and the virtues annexed to it....Therefore there can be no moral virtue without prudence [practical wisdom], and consequently neither can there be without understanding. For it is by the virtue of understanding that we know naturally known principles both in speculative and practical matters.

S. Th., I-II, Q. 58, Art. 4 (Pegis, p. 446)

4. For the formal principle of the virtue of which we speak now is the good as defined by reason. This good can be considered in two ways. First, as existing in the consideration itself of reason, and thus we have one principal virtue called prudence [practical wisdom]. Secondly, according as the reason puts its order into something else, and this either into operations [external actions], and then we have justice, or into passions, and then we need two virtues. For the need of putting the order of reason into the passions is due to their thwarting reason; and this occurs in two ways. First, when the passions incite to something against reason, and then they need a curb, which we thus call temperance [self-control]; secondly, when the passions withdraw us from following the dictate of reason. e.g., through fear of danger or toil, and then man needs to be strengthened for that which reason dictates, lest he turn back, and to this end there is fortitude [courage, bravery].

S. Th., I-II, Q. 61, Art. 2 (Pegis, p. 468)

B. The Structure of Natural Law

5. Law is nothing else than an ordinance of reason for the common good, promulgated by him who has the care of the community....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.

S. Th., I-II, Q. 90, Art. 4 (Pegis, p. 747)

6. ...Law, being a rule and measure, can be in a person in two ways: in one way, as in him that rules and measures; in another way, as in that which is ruled and measured, since a thing is ruled and measured in so far as it partakes of the rule or measure. Therefore, since all things subject to divine providence are ruled and measured by the eternal is evident that all things partake in some way in the eternal law, in so far as, namely, from its being imprinted on them, they derive their respective inclinations to their proper acts and ends. Now among all others, the rational creature is subject to divine providence in a more excellent way, in so far as it itself partakes of a share of providence, by being provident both for itself and for others. Therefore it has a share of the eternal reason, whereby it has a natural inclination to its proper act and end; and this participation of the eternal law in the rational creature is called the natural law.

S. Th., I-II, Q. 91, Art. 2 (Pegis, pp. 749-750)

7. ...The precepts of the natural law are to the practical reason what the first principles of demonstrations are to the speculative [theoretical] 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; even though it may happen that to one who does not know the definition of the subject, such a proposition is not self-evident. For instance, this proposition, Man is a rational being, is, in its very nature, self-evident, since he who says man, says a rational being; and yet to one who does not know what a man is, this proposition is not self-evident....Now as being is the first thing that falls under the apprehension absolutely, so good is the first thing that falls under the apprehension of the practical reason, which is directed to action (since every agent acts for an end, which has the nature of good). Consequently, the first principle in the practical reason is one founded on the nature of good, viz., that good is that which all things seek after. Hence this is the first precept of law, that good is to be done and promoted, and evil is to be avoided. All other precepts of the natural law are based upon this; so that all the things which the practical reason naturally apprehends as man's good belong to the precepts of the natural law under the form of things to be done or avoided.

Since, however, good has the nature of an end, and evil, the nature of the contrary, hence it is that all those things to which man has a natural inclination are naturally apprehended by reason as being good, and consequently as objects of pursuit, and their contraries as evil, and objects of avoidance. Therefore, the order of the precepts of natural law is according to the order of natural inclinations. For there is in man, first of all, an inclination to good in accordance with the nature which he has in common with all substances, inasmuch, namely, as every substance seeks the preservation of its own being, according to its nature; and by reason of this inclination, whatever is a means to preserving human life, and of warding off its obstacles, belongs to the natural law. Secondly, there is in man an inclination to things that pertain to him more specially, according to that nature which he has in common with other animals; and in virtue of this inclination, those things are said to belong to the natural law which nature has taught all animals, such as sexual intercourse, the education of offspring and so forth. Thirdly, there is in man an inclination to do good according to the nature of his reason, which nature is proper to him. Thus man has a natural inclination to know the truth about God, and to live in society; and in this respect, whatever pertains to this inclination belongs to the natural law: e.g., to shun ignorance, to avoid offending those among whom one has to live, and other things regarding the above inclination.

S. Th., I-II, Q. 94, Art. 2 (Pegis, pp. 774-775)

C. Moral Precepts Derived From Natural Reason

8. It is ... evident that since the moral precepts are about matters which concern good morals; and since good morals are such as are in accord with reason; and since every judgment of human reason must needs be derived in some way from natural reason, it follows, of necessity, that all the moral precepts belong to the law of nature, but not all in the same way. For there are certain things which the natural reason of every man, of his own accord and at once, judges to be done or not to be done: e.g., Honor thy father and thy mother, and, Thou shalt not kill, Thou shalt not steal (Exod. xx 12, 13, 15): and these things belong to the law of nature absolutely. And there are certain things which, after a more careful consideration, wise men deem obligatory. Such belong to the law of nature, yet so that they need to be inculcated, the wiser teaching the less wise: e.g., Rise up before the hoary head, and honor the person of the aged man (Levit. xix. 32), and the like.

S. Th., I-II, Q. 100, Art. 1 (Pegis, p. 828)

9. That a man should not do harm to anyone is an immediate dictate of his natural reason, and therefore the precepts of the Decalogue [the Ten Commandments] that forbid the doing of harm are binding on all men. But it is not an immediate dictate of the natural reason that a man should do one thing in return for another, unless he happen to be indebted to someone. Now a son's debt to his father is so evident that one cannot get away from it by denying it; for the father is the principle of generation and being, and also of upbringing and teaching.

S. Th., I-II, Q. 100, Art. 5 (Pegis, p. 837)

10. To his neighbors a man behaves himself well both in particular and in general: in particular, as to those to whom he is indebted, by paying his debts: and in this sense is to be taken the commandment about honoring one's parents; in general, as to all men, by doing harm to none, either by deed, or by word, or by thought. By deed, harm is done to one's neighbor, sometimes in his person, i.e., as to his personal existence, and this is forbidden by the words, Thou shalt not kill; sometimes in a person united to him, as to the propagation of offspring, and this is prohibited by the words, Thou shalt not commit adultery; sometimes in his possessions, which are directed to both the aforesaid, and with regard to this it is said, Thou shalt not steal. Harm by word is forbidden when it is said, Thou shalt not bear false witness against thy neighbor; and harm done by thought is forbidden in the words, Thou shalt not covet [have excessive desire for that which belongs to someone else].

S. Th., I-II, Q. 100, Art. 5 (Pegis, p. 835)

D. Secondary Principles Not Always Applicable

11. As we have stated above, to the natural law belong those things to which man is inclined naturally; and among these it is proper to man to be inclined to act according to reason. Now it belongs to the reason to proceed from what is common to what is proper [specific] as is stated in [Aristotle's] Physics i. The speculative [theoretical] reason, however, is differently situated in this matter, from the practical reason. For, since the speculative [theoretical] reason is concerned chiefly with necessary things, whch cannot be otherwise than they are, its proper [specific] conclusions, like the universal principles, contain the truth without fail. The practical reason, on the other hand, is concerned with contingent matters, which is the domain of human actions; and, consequently, although there is necessity in the common principles, the more we descend towards the particular, the more frequently we encounter defects. Accordingly, then, in speculative [theoretical] matters truth is the same in all men, both as to principles and as to conclusions; although truth is not known to all as regards the conclusions, but only as regards the principles....But in matters of action, truth or practical rectitude is not the same for all as to what is particular, but only as to common principles; and where there is the same rectitude in relation to particulars, it is not equally known to all....Thus, it is right and true for all to act according to reason, and from this principle it follows, as a proper [specific] conclusion, that goods entrusted to another should be restored to their owner. Now this is true for the majority of cases. But it may happen in a particular case that it would be injurious, and therefore unreasonable, to restore goods held in trust; for instance, if they are claimed for the purpose of fighting against one's country. And this principle will be found to fail all the more, according as we descend further towards the particular, e.g., if one were to say that goods held in trust should be restored with such and such guarantee, or in such and such a way; because the greater the number of conditions added, the greater the number of ways in which the principle may fail, so that it be not right to restore or not to restore.

S. Th., I-II, Q. 94, Art. 4 (Pegis, pp. 777-778)

12. A change in the natural law may be understood in two ways. First, by way of addition. In this sense, nothing hinders the natural law from being changed, since many things for the benefit of human life have been added over and above the natural law, both by the divine law and by human laws. Secondly, a change in the natural law may be understood by way of subtraction, so that what previously was according to the natural law, ceases to be so. In this sense, the natural law is altogether unchangeable in its first principles. But in its secondary principles, which, as we have said, are certian detailed proximate conclusions drawn from the first principles, the natural law is not changed so that what it prescribes be not right in most cases. But it may be changed in some particular cases of rare occurrence, through some special causes hindering the observance of such precepts, as was stated above.

S. Th., I-II, Q. 94, Art. 5 (Pegis, p. 779)

E. Human Law and Conscience

13. As Augustine says (De Lib. Arb. i, 5) “that which is not just seems to be no law at all”:

wherefore the force of a law depends on the extent of its justice. Now in human affairs a thing is said to be just, from being right, according to the rule of reason. But the first rule of reason is the law of nature, as is clear from what has been stated above (q. 91, a. 2, ad 2). Consequently every human law has just so much of the nature of law, as it is derived from the law of nature. But if in any point it deflects from the law of nature, it is no longer a law but a perversion of law. But it must be noted that something may be derived from the natural law in two ways: first, as a conclusion from premises, secondly, by way of determination of certain generalities. The first way is like to that by which, in sciences, demonstrated conclusions are drawn from the principles: while the second mode is likened to that whereby, in the arts, general forms are particularized as to details: thus the craftsman needs to determine the general form of a house to some particular shape. Some things are therefore derived from the general principles of the natural law, by way of conclusions; e.g. that “one must not kill” may be derived as a conclusion from the principle that “one should do harm to no man”: while some are derived therefrom by way of determination; e.g. the law of nature has it that the evil doers should be punished; but that he be punished in this or that way, is a determination of the law of nature. Accordingly both modes of derivation are found in the human law. But those things which are derived in the first way, are contained in human law not as emanating therefrom exclusively, but have some force from the natural law also. But those things which are derived in the second way, have no other force than that of human law.

S. Th., I-II, Q. 95, Art. 2 (Pegis, p. 784-5)

14. Laws framed by man are either just or unjust. If they be just, they have the power of binding in conscience, from the eternal law whence they are derived, according to Prov. 8:15: “By Me kings reign, and lawgivers decree just things.” Now laws are said to be just, both from the end, when, to wit, they are ordained to the common good—and from their author, that is to say, when the law that is made does not exceed the power of the lawgiver—and from their form, when, to wit, burdens are laid on the subjects, according to an equality of proportion and with a view to the common good. For, since one man is a part of the community, each man in all that he is and has, belongs to the community; just as a part, in all that it is, belongs to the whole; wherefore nature inflicts a loss on the part, in order to save the whole: so that on this account, such laws as these, which impose proportionate burdens, are just and binding in conscience, and are legal laws. On the other hand laws may be unjust in two ways: first, by being contrary to human good, through being opposed to the things mentioned above—either in respect of the end, as when an authority imposes on his subjects burdensome laws, conducive, not to the common good, but rather to his own cupidity or vainglory—or in respect of the author, as when a man makes a law that goes beyond the power committed to him—or in respect of the form, as when burdens are imposed unequally on the community, although with a view to the common good. The like are acts of violence rather than laws; because, as Augustine says (De Lib. Arb. i, 5), “a law that is not just, seems to be no law at all.” Wherefore such laws do not bind in conscience, except perhaps in order to avoid scandal or disturbance, for which cause a man should even yield his right, according to Mat. 5:40,41: “If a man. . . take away thy coat, let go thy cloak also unto him; and whosoever will force thee one mile, go with him other two.” Secondly, laws may be unjust through being opposed to the Divine good: such are the laws of tyrants inducing to idolatry, or to anything else contrary to the Divine law: and laws of this kind must nowise be observed, because, as stated in Acts 5:29, “we ought to obey God rather than man.”

S. Th., I-II, Q. 96, Art. 4 (Pegis, p. 794-5)

F. The Doctrine of Double Effect

15. Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental as explained above (43, 3; I-II, 12, 1). Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists [Cap. Significasti, De Homicid. volunt. vel casual.], "it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense." Nor is it necessary for salvation that a man omit the act of moderate self-defense in order to avoid killing the other man, since one is bound to take more care of one's own life than of another's. But as it is unlawful to take a man's life, except for the public authority acting for the common good, as stated above (Article 3), it is not lawful for a man to intend killing a man in self-defense, except for such as have public authority, who while intending to kill a man in self-defense, refer this to the public good, as in the case of a soldier fighting against the foe, and in the minister of the judge struggling with robbers, although even these sin if they be moved by private animosity.

S. Th., II-II, Q. 64, Art. 7 (not included in Pegis)

G. Human Law Does Not Repress All Vices

…law is framed as a rule or measure of human acts. Now a measure should be homogeneous with that which it measures, as stated in Metaph. x, text. 3,4, since different things are measured by different measures. Wherefore laws imposed on men should also be in keeping with their condition, for, as Isidore says (Etym. v, 21), law should be "possible both according to nature, and according to the customs of the country." Now possibility or faculty of action is due to an interior habit or disposition: since the same thing is not possible to one who has not a virtuous habit, as is possible to one who has. Thus the same is not possible to a child as to a full-grown man: for which reason the law for children is not the same as for adults, since many things are permitted to children, which in an adult are punished by law or at any rate are open to blame. In like manner many things are permissible to men not perfect in virtue, which would be intolerable in a virtuous man. Now human law is framed for a number of human beings, the majority of whom are not perfect in virtue. Wherefore human laws do not forbid all vices, from which the virtuous abstain, but only the more grievous vices, from which it is possible for the majority to abstain; and chiefly those that are to the hurt of others, without the prohibition of which human society could not be maintained: thus human law prohibits murder, theft and such like…. The purpose of human law is to lead men to virtue, not suddenly, but gradually. Wherefore it does not lay upon the multitude of imperfect men the burdens of those who are already virtuous, viz. that they should abstain from all evil. Otherwise these imperfect ones, being unable to bear such precepts, would break out into yet greater evils: thus it is written (Psalm 30:33): "He that violently bloweth his nose, bringeth out blood"; and (Matthew 9:17) that if "new wine," i.e. precepts of a perfect life, "is put into old bottles," i.e. into imperfect men, "the bottles break, and the wine runneth out," i.e. the precepts are despised, and those men, from contempt, break into evils worse still…. The natural law is a participation in us of the eternal law: while human law falls short of the eternal law. Now Augustine says (De Lib. Arb. i, 5): "The law which is framed for the government of states, allows and leaves unpunished many things that are punished by Divine providence. Nor, if this law does not attempt to do everything, is this a reason why it should be blamed for what it does." Wherefore, too, human law does not prohibit everything that is forbidden by the natural law.

S. Th., I-II, Q. 96, Art. 2 (Pegis, pp. 792-93)