An Exposition of "Inclination" in Thomas Aquinas' Treatise on Law

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Questions 90 through 108 of the Prima Secundae constitute Thomas Aquinas’ Treatise on Law.[1] In this portion of the Summa Theologiae, Thomas is concerned with several questions related to the nature of law and to what he calls natural law. His purpose is to show, first, that there are four kinds of law—Eternal Law, Natural Law, Human Law, and Divine Law—and second, that these laws work in unison to accomplish God’s will in all that He has created.

In making this argument, Thomas repeatedly employees the concept of inclination. Thomas begins the treatise with a reference to this idea. In the first paragraph of the treatise, he says:

We have now to consider the extrinsic principles of acts. Now the extrinsic principle inclining to evil is the devil, of whose temptations we have spoken in the FP, Q114. But the extrinsic principle moving to good is God, Who both instructs us by means of His Law, and assists us by His Grace: wherefore in the first place we must speak of law; in the second place, of grace.[2]

In Article 1 of the same question, he answers:

In this way, law is in all those things that are inclined to something from 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.[3]

From this starting point, Thomas’ discussion of law unfolds over dozens of pages and by the use of this concept dozens of times. The centrality of this idea to several components of Aquinas’ moral and legal theory is evident in the sixty occurrences of the term inclination and its various forms (inclinations, incline, inclined, inclines, inclining) in twenty-one paragraphs across the nineteen questions of the treatise. The concept of inclination is of particular importance to Aquinas’ discussion of natural law (Q. 94) where the greatest number of references is found. Note, for example, the following quote from Question 94, Article 2:

Since, however, good has the nature of an end, and evil, the nature of a 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. Wherefore according to the order of natural inclinations, is the order of the precepts of the natural law. [4]

These are only two of the ten references to inclination in this one paragraph. Given the obvious significance of the concept of inclination for Aquinas’ moral and legal theory, it behooves the student of Aquinas to understand this concept as Aquinas employees it. In this article, I will offer an expository definition of inclination by examining Thomas’ use of the term in its various forms in his treatise on law and I will give a brief explanation of the role of inclination in Thomas’ moral and legal theory.

Preliminaries to an Expository Definition

The English term inclination can mean, among other things, “a tendency to a particular aspect, state, character, or action” and “a particular disposition of mind or character,” or, “natural disposition.”[5] If we take the English term inclination to be the proper translation of Thomas’ original term inclinatio then it seems that we could safely assume that Thomas means by inclinatio something like what the English term inclination means—to be disposed to a certain end or action or, to possess a disposition of mind or a tendency of character. While much indeed could be said on this point by way of historical contextualization and by way of differentiation from misuses,[6] this term has been commonly misunderstood as mere biological urges or as the deliverances of rational thought, the scope of this paper limits our definition of inclination and its related forms to what may be discovered as we examine Thomas’ use of the term in his treatise on law. Additionally, though I will briefly note Aquinas’ use of inclination in reference to vegetable and animal life, I will focus primarily on inclination in reference to humans.

Inclination as a Disposition to Act

For Aquinas, human actions are subject to law as moral actions. To discuss law, then, is to discuss the causes and regulations of human actions. And to discuss law in the context of God’s will for His creation is to discuss causes of actions in the context of God as primary cause. It is with this point, the causes or principles of acts, that Thomas begins his discussion of law. He says:

We have now to consider the extrinsic principles of acts. Now the extrinsic principle inclining to evil is the devil, of whose temptations we have spoken in the FP, Q114. But the extrinsic principle moving to good is God, Who both instructs us by means of His Law, and assists us by His Grace: wherefore in the first place we must speak of law; in the second place, of grace.[7]

From this text it may be observed that one can be inclined to evil acts. This inclination comes from an extrinsic principle, a source external to the actor, namely, the devil. The meaning of Aquinas’ statement here is simply that the devil can influence a person to do evil through temptation. In the third sentence of this quotation, Aquinas gives us an insight into what he means by “inclining” as he says by contrast to the devil, that “the extrinsic principle moving to good is God.” Note, God, as an extrinsic principle, moves human beings to good acts, or, to do good. Thus, Aquinas uses inclining and moving to interchangeably. In this first use of the term, to incline to is to move to act. We might say, then, that inclination is a disposition to act, either for good or evil.

Aquinas uses inclination in the same way in Article 1 of Question 90, where he says,

In this way, law is in all those things that are inclined to something from 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.[8]

Notice, things are “inclined to something.” In the case of the members of the body, they have “the inclination…to concupiscence.” Aquinas means that the members of the body are disposed to acts of lust, a point which he will discuss in greater detail in Question 91.

This meaning of inclination is given explicitly in Question 91, Article 2. There Thomas writes,

[I]t is evident that all things partake somewhat of the eternal law, insofar 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 the most excellent way, insofar as it partakes of a share of providence, by being provident both for itself and for others. Wherefore 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.[9]

Twice in this section, Aquinas refers to an inclination to act. Again, this statement seems to convey the meaning of a disposition to act. In this case, Aquinas seems to mean that things have dispositions to acts that are proper to their natures and that, therefore, correspond to God’s law. While Aquinas indicates here that we can know more about inclinations than that they are dispositions to acts, they also pertain to ends, he does, nevertheless, explicitly indicate that an inclination is a disposition to act.

The use of inclination as disposition to act is evident again in Question 91, Article 6. In a discussion of the law of sin, Aquinas says:

Now those who are subject to a law may receive a twofold inclination from the lawgiver. First, insofar as he directly inclines his subjects to something; sometimes indeed different subjects to different acts; in this way we may say that there is a military law and a mercantile law. Second, indirectly; thus by the very fact that a lawgiver deprives a subject of some dignity, the latter passes into another order, so as to be under another law, as it were: thus if a soldier be turned out of the army, he becomes a subject of rural or of mercantile legislation.[10]

Again, as in the previous passages cited, Aquinas uses inclination and inclines to refer to a disposition to act. In this case, he says explicitly, “…he directly inclines his subjects to something; sometimes indeed different subjects to different acts.”

Consider finally, Aquinas’ important statement concerning inclination as disposition to act in Question 94, Article 3. He writes,

For it has been stated (A2) that to the natural law belongs everything to which a man is inclined according to his nature. Now each thing is inclined naturally to an operation that is suitable to it according to its form: thus fire is inclined to give heat. Wherefore, since the rational soul is the proper form of man, there is in every man a natural inclination to act according to reason: and this is to act according to virtue.[11]

In this passage, Aquinas says that things are inclined to operations. He specifically says of humans that they are inclined to acts. While we might cite additional passages that make this first point, we will allow these to suffice to show that by inclination Aquinas means a disposition to act. It should be noted from this last reference, that the human inclination to act is an inclination to act according reason and according to virtue. This statement directs our attention to the next point of our definition.

Inclination as Disposition to Act According to Ends Appropriate to Nature

If, as Aquinas argues, we are, by inclination, disposed to act, then we cannot help but wonder, act how? In what way? For what purposes? In other words, we will naturally want to know in what manner we are disposed to act. In his treatise on law and elsewhere, Aquinas is clear that our inclination is to act according to ends, that is, for goals or purposes. In Question 91, Article 2, Thomas says that “all things partake somewhat of the eternal law, insofar as, namely, from its being imprinted on them, they derive their respective inclinations to their proper acts and ends.”[12]

In referring to “proper acts and ends,” Aquinas indicates the natural teleology of all things. All things are designed for ends according to the final causes of God for them. Inclinations in things are according to the ends proper to them. And what is proper for a thing is determined by its nature—its essence.

He elaborates on this idea in Question 94. There he indicates that each kind of thing has an end or ends that are appropriate to its nature:

Since, however, good has the nature of an end, and evil, the nature of a 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. Wherefore according to the order of natural inclinations, is the order of the precepts of the natural law. Because in man there is first of all an inclination to good in accordance with the nature which he has in common with all substances: inasmuch as every substance seeks the preservation of its own being, according to its nature: and by reason of this inclination, whatever is a means of preserving human life, and of warding off its obstacles, belongs to the natural law. Second, 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 to all animals, such as sexual intercourse, education of offspring and so forth. Third, there is in man an inclination to 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; for instance, to shun ignorance, to avoid offending those among whom one has to live, and other such things regarding the above inclination.[13]

Notice, Aquinas describes man’s nature as substance, as animal, and as rational soul. According to Aquinas, man has inclinations which correspond to each of these aspects of his nature. First, like all substances including the vegetable substances, man is inclined to preserve his life. Second, as is true of all animals, man is inclined to produce offspring. Uniquely, man is also inclined to educate his offspring. Third, according to his rational nature, man is inclined to seek truth and know God, and to live in society. In addition to these inclinations, man has as his primary inclination, the disposition to avoid evil and seek the good.

In the next article, Thomas will say that the ends that a thing pursues are those ends that are suitable for it. He writes, “Now each thing is inclined naturally to an operation that is suitable to it according to its form.”[14] Here suitable has the idea of proper as in the previous article. If we were to ask, why is something suitable for a thing according to its nature, Thomas’ answer would be something like, “because God made it that way.” That is, the nature of man according to which inclinations are ordered is a nature impressed upon it by God. In Question 91, Article 2, Thomas writes:

Wherefore, since all things subject to Divine providence are ruled and measured by the eternal law, as was stated above (A1); it is evident that all things partake somewhat of the eternal law, insofar as, namely, from its being imprinted on them, they derive their respective inclinations to their proper acts and ends.[15]

Our inclinations, thus, are derived from God’s eternal law imprinted upon us.[16]

Importantly, our natural ends are good and we come to know them via reason. In the lengthy citation from Question 94, Article 2 above, Aquinas says “all those things to which man has a natural inclination, are naturally apprehended by reason as being good.”[17] This statement helps us understand the end of our inclinations as the good. Though we may not, in actuality, pursue the good, God has designed us for the good. Our proper, natural purpose is the good. If we act according to our proper, natural purpose, we will pursue the good and avoid the evil. How do we discern what it means to pursue the good and avoid the evil? According to Thomas, we use reason to apprehend in our inclinations the goods we are to pursue. In other words, if we examine our natural dispositions to act according to ends suiting our nature, that is, our inclinations, then we will by reason, be able to abstract from these dispositions basic moral principles by which we may guide our behavior, principles like avoid evil and do good.

Inclination as the Source of the Precepts of Natural Law

As I noted above, Aquinas’ discussion of inclination in the treatise on law especially focuses on the natural law. The natural law, as Thomas defines it, is “the rational creature’s participation of the eternal law.”[18] Thomas has several things to say about the connection between inclination and natural law. First, in Question 94, Article 4, he says “to the natural law belongs those things to which a man is inclined naturally.”[19] He emphasizes the connection between natural law and reason here as he goes on to say, “and among these it is proper to man to be inclined to act according to reason.”[20] Notice again that Aquinas does not equate inclination to reason. Rather, he says that we are inclined to act according to reason.

Inclination, however, does serve as the raw material on which reason acts and by which it apprehends the precepts or commands of the natural law. Thomas calls those principles at which reason arrives from an examination of our inclinations, the precepts of natural law. According to Question 91, Article 4, Adversus 2, they are “principles imparted by nature, which are the precepts of the natural law.”[21] He explains what he means by this in a lengthy statement in Question 91, Article 2:

Wherefore 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. Hence the Psalmist after saying (Ps 4:6): Offer up the sacrifice of justice, as though someone asked what the works of justice are, adds: Many say, Who showeth us good things? in answer to which question he says: The light of Thy countenance, O Lord, is signed upon us: thus implying that the light of natural reason, whereby we discern what is good and what is evil, which is the function of the natural law, is nothing else than an imprint on us of the Divine light. It is therefore evident that the natural law is nothing else than the rational creature’s participation of the eternal law.[22]

When reason apprehends these principles from our natural inclinations and then applies them to discern good and evil, the natural law is functioning in us. Later, in Question 94, Article 2, he specifically says, “whatever the practical reason naturally apprehends as man’s good (or evil) belongs to the precepts of the natural law as something to be done or avoided.”[23]

In these statements, Aquinas is pointing to those principles gathered from inclination as the foundational precepts of natural law. He compares these precepts to the indemonstrable foundational precepts of speculative reason. He writes:

Now a certain order is to be found in those things that are apprehended universally. For that which, before aught else, falls under apprehension, is being, the notion of which is included in all things whatsoever a man apprehends. Wherefore the first indemonstrable principle is that the same thing cannot be affirmed and denied at the same time, which is based on the notion of being and not-being: and on this principle all others are based, as is stated in Metaph. iv, text. 9. Now as being is the first thing that falls under the apprehension simply, 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 under the aspect of good. Consequently the first principle of practical reason is one founded on the notion 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 pursued, and evil is to be avoided. All other precepts of the natural law are based upon this: so that whatever the practical reason naturally apprehends as man’s good (or evil) belongs to the precepts of the natural law as something to be done or avoided.[24]

In that the principles gathered from inclination serve as the foundational precepts of the natural law, we can safely say that there would be no natural law as it now is were it not for the inclinations of our nature.

More generally we can say that in that practical reasoning, that process by which we make everyday judgments about right and wrong, is based on the principles discovered through inclination, inclination is the font of moral decision-making. Aquinas says, “Wherefore according to the order of natural inclinations, is the order of the precepts of the natural law .”[25] In so arguing, Aquinas rejects the Naturalistic Fallacy of Moore and the Is-Ought Problem of Hume. Aquinas, instead, says that we can apprehend from what is, what ought to be. We can see in our nature, particularly our natural inclinations, how we ought to act. As such, we have a solid grounding for moral judgments, our inclinations, and that because we have a solid grounding for moral facts, God’s will which orders our inclinations.

Inclination as Indirect Source for Human Law

Of human law and its relation to natural law, Aquinas says:

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 (Q91, A2, 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.[26]

Here Aquinas argues that human law is law insofar as it agrees with the law of nature. By this he means that any human law which violates the natural law, though it is called a law, is not actually a law. It does not partake in the character of law. This dependency of human law on natural law raises to our attention the connection between human law and inclination. In that human law is law if it is derived from natural law, and in that the precepts of natural law are ordered by our natural inclinations, it can be said that our inclinations indirectly order human law. Thus, in grounding moral knowledge in the principles derived from our inclinations, Aquinas also secures a grounding of knowledge for just laws. Therefore, while inclinations themselves are not the law, they are the font of the principles by which just precepts of law may be established and promulgated.

Aquinas considers several complications associated with this theory which, if unresolved, would call into question his natural law theory and the inclinations at their foundation. He asks whether all human laws must be the same in order for his natural law theory to offer the proper grounding for the human law and he answers no. Particular laws of different places and different times will be different, in part, because of different needs and circumstances and, in part, because any number of particular laws could accomplish the same particular end within the common good for a society. He also considers errors in human judgment and law and asks how these might impact his natural law theory and the underlying claim of inclinations. To this concern he concedes that there are instances in which man errs in his laws. The Germans, he notes, once believed it was permissible to spoil defeated enemies.[27] Though this was law, it was defective law as it failed to comport with the principles of the natural law. He also explores the possibility of the change of human laws. Again, he says these laws may be added to the natural law to carry out some principle of the law or subtracted if they no longer accomplish the precepts of the natural law. Having entertained these different questions, however, he holds firm to the ordering precepts of the natural law and that, on the basis of the unchanging nature of man and of man’s inclinations.

Conclusion

Inclinations, those dispositions to act according to ends appropriate to our nature, serve as the raw material from which reason may apprehend principles of good and evil. These principles order the precepts of natural law, and natural law governs moral judgments and human law. Thus, it would be almost impossible to overstate the importance of inclinations in Thomas’ natural law moral and legal theory. Even so, we do well to notice that several important conclusions follow from Thomas’ doctrine of inclinations. If Thomas is right about inclinations, then, first, we have a nature ordered by God. Second, the order of our nature is evidence for the existence of God. Third, the order of our nature as revealed in our inclinations is a proper basis for moral knowledge. Fourth, we can assess any, and all, human laws by comparing them to natural law in light of our inclinations. Fifth, we can conclude that that which goes against our natural inclinations is not, itself, natural or proper. Finally, we can seek out God’s law for instructions and we can pray for God’s grace for assistance as we seek to understand our inclinations and their proper pursuit in our lives. If Thomas is right, pursuing our inclinations fully, will perfect us as persons, bringing us felicity now, and full happiness in heaven.

[1]Summa Theologiae. Aquinas. Accessed April 29, 2022. https://aquinas.cc/la/en/~ST.I-II.Q94.A5.SC. [2] Aquinas, ST. I-II, Q.90, A1. [3] Aquinas, ST. I-II, Q.90, A1. [4] Aquinas, ST. I-II, Q. 94, A2 [5] https://www.merriam-webster.com/dictionary/inclination?utm_campaign=sd&utm_medium=serp&utm_source=jsonld#other-words [6] Cunningham, Sean B. “The Catholic University of America Natural Inclination in ... - WRLC.” Accessed April 30, 2022. https://cuislandora.wrlc.org/islandora/object/etd%3A374/datastream/PDF/view. [7] Aquinas, ST. I-II, Q. 90, A1. [8] Aquinas, ST. I-II, Q. 90, A1. [9] Aquinas, ST. I-II, Q. 90, A1. [10] Aquinas, ST. I-II, Q. 91, A6. [11] Aquinas, ST. I-II, Q. 90, A1. [12] Aquinas, ST. I-II, Q. 91, A2. [13] Aquinas, ST. I-II, Q. 94, A2. [14] Aquinas, ST. I-II, Q. 94, A3. [15] Aquinas, ST. I-II, Q. 91, A2. [16] It may be worth noting that Thomas simply asserts that man’s nature is this way. For Thomas, this is obvious. We can see this in ourselves and others. In fact, to deny this would be embarrassing as Thomas sees it. In this sense, he adopts a common-sense realist approach to man’s nature which follows the Aristotelian tradition. Man has a nature as a rational animal. He seeks the good as it fits his nature. [17] Aquinas, ST. I-II, Q. 94, A2. [18] Aquinas, ST. I-II, Q. 91, A2. [19] Aquinas, ST. I-II, Q. 94, A4. [20] Aquinas, ST. I-II, Q. 94, A4. [21] Aquinas, ST. I-II, Q. 91, A4, Ad2. [22] Aquinas, ST. I-II, Q. 91, A2. [23] Aquinas, ST. I-II, Q. 94, A2. [24] Aquinas, ST. I-II, Q. 94, A2. [25] Aquinas, ST. I-II, Q. 94, A2. [26] Aquinas, ST. I-II, Q. 95, A1. [27] Aquinas, ST. I-II, Q. 94, A4.