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Chapter IV -- 14

St Thomas begins his analysis of human action by referring to St John of Damascus.[1] He establishes that a voluntary act is an act which is a rational operation. St Thomas establishes that a voluntary act or movement has two elements: that the agent act by an internal principle—that is, not be moved from without—, and that the agent act for an end. He writes:

For this is the import of the word ‘voluntary’, that the movement and the act are from the [agent’s] own inclination. And that is what the ‘voluntary’ is said to be according to the definition of Aristotle, St Gregory of Nyssa and St John of Damascus: not only that ‘of which the principle is internal’, but with the addition of knowledge (scientia).[2]

St Thomas means by ‘knowledge’: conscious, rational apprehension or understanding of the end, accompanied by deliberation over the end and over the means to the end.

St Thomas establishes that animals, although deprived of reason, have the exercise of the ‘voluntary’.[3] However, since they have an imperfect knowledge of the end—a mere sense-perception of the object that constitutes the end—that voluntary aspect of their actions is imperfect in comparison with the voluntary aspect of human actions. He writes:

Therefore in its perfect sense (rationem), the ‘voluntary’ follows perfect knowledge (cognitionem) of the end—as, that is to say, someone, by the apprehension of the end, and after deliberating over the end and over those things which are towards the end, is able to be moved towards the end or not to be moved. However, in an imperfect sense, the ‘voluntary’ follows imperfect knowledge of the end—as, that is to say, apprehending the end, one does not deliberate, but is moved suddenly to that very end. Whence, the ‘voluntary’ in its perfect sense is appropriate only to the rational nature, but in its imperfect sense it is appropriate even to the brute animals.[4]

We see here the great emphasis that St Thomas places on the reason in his analysis of the ‘voluntary’. The ‘voluntary’ taken in its perfect sense is to be found only in those cases where the end of the action—in St Thomas, actions which are not for a determinate, concrete end cannot be voluntary—is fully known by the reason and where deliberation by the reason over the end and over the means to the end precedes a decision whether to proceed to the end or not to proceed at all. However, in cases where a passion overwhelms the man and without deliberation he is suddenly moved towards the determinate, concrete end of the passion or, to take another example, in cases where a brute animal is moved by a similar irrational movement of the sensitive appetite, then the action is still voluntary, but only in an imperfect sense.

St Thomas elsewhere remarks that to the extent that a man’s reason is incapacitated by this sudden overwhelming by the passion—which overwhelming, St Thomas observes, always has a bodily substrate—then the will does not operate.[5] How can such an action be voluntary ‘in an imperfect sense’, as St Thomas is saying here,[6] without the will being in operation, as he is saying elsewhere?[7] Can, in St Thomas’ doctrine, an action be voluntary, even in an imperfect sense, without the will being in operation? For according to St Thomas, the actions of a brute animal are in an imperfect sense voluntary, even though brute animals necessarily lack will, since they lack reason, and the will is a rational appetite. Of course, St Thomas wishes to preserve the voluntariness of the movements of brute animals towards food or sexual union, or on account of anger or rage, and the voluntariness of similar movements in man when the reason is not in control; but he wishes also, for the sake of his moral analysis, to distinguish sharply between such movements in man, and actions which are done by a man on the basis of cool, rational deliberation about ends and means.

St Thomas himself solves this puzzle.[8] He explains that only rational beings have a will, which is a rational appetite, but ‘voluntary’ can still be used in those cases where there is a certain participation in the will according to a harmony with the will, and that in this sense ‘voluntary’ is attributed to the brute animals, that is to say, to the extent that by means of a certain knowledge (i.e. sense-perception) they are moved to their end.

St Thomas is here defining the broad outlines of his doctrine of human action: human actions are those in which the man rationally understands his end and rationally deliberates over that end and over the means to attain it. Actions done by a man that lack rational comprehension of the end and deliberation over the end and over the means to attain it are not human actions, although they certainly are actions done by a man. St Thomas never departs from this framework.

It is here, strangely enough, the St Thomas provides the first cue to the researcher into artificial intelligence wishing to design a robot: limit the actions that the robot will accomplish to those that fit this determinate, rationalistic model of human action; and, moreover, resolve the basic model of the robot’s actions into a rational evaluation and adoption of an end and deliberation over—algorithmic search for and evaluation of—various means to attain that end, followed by execution of the means selected, so that the adopted end is attained.

St Thomas establishes that the ‘voluntary’ can exist even without overt action, since either we may want not to act or we may not want to act—these are two different things. He writes:

That is called the ‘voluntary’ which is said to be from the will. In one manner, directly, because, that is to say, it proceeds from another thing inasmuch as that thing is the agent, as heating proceeds from heat. In another way, indirectly, from the very fact that the other thing does not act, just as the sinking of the ship is said to be from the captain inasmuch as he desisted from navigating.

But it must be known that that which follows a deficiency of action is not always reduced to the agent, as to its cause, from the fact that the agent did not act, but only then, when he could and should have acted. Therefore, if the captain were not able to direct the ship, or if the navigation of the ship had not been entrusted to him, the sinking of the ship would not be imputed to him, that sinking which occurred through the absence of a captain. When, therefore, the will, by willing and acting, can prevent that which is ‘not to will’ and ‘not to act’, and sometimes must, then that which is ‘not to will’ and ‘not to act’ is imputed to it as if existing by that very fact; and thus the ‘voluntary’ can come to exist without act: in some cases, without an exterior act but with an interior act, as when one wills not to act; at another time, however, even without an interior act, as when one does not will [to act].[9]

We can here see the legalism of St Thomas’ approach to moral theology. This is reasoning suitable to a law-book on negligence. Indeed, in St Thomas there is no discontinuity between moral theology and the law: the one flows imperceptibly into the other in a unitary social world in which the theologian analyses moral issues so that the legislator can write the appropriate laws to implement the moral judgements of the Church. In this regard, The Pocket Aquinas contains a very interesting letter of St Thomas in which he replies to an invitation to analyse the moral implications of the practice in the fabric trade at Florence of offering discounts for quick payment of commercial accounts, evidently so that the authorities at Florence can properly regulate this practice.[10] There is no sense in St Thomas of the modern post-Christian world in which the secular law is primary and religion is a private ‘matter of conscience’ completely subordinate to the secular state.

To continue with our remarks on the use of St Thomas’ model in the design of robots, St Thomas here distinguishes two special cases in the selection of an end: the decision not to act and the decision not to decide whether or not to act. These are real alternatives.

In the case of human moral actions, St Thomas is saying that in some cases either of these two alternatives conveys moral responsibility for the consequences of the inaction. This is a doctrine of moral negligence.

St Thomas establishes that the will cannot be forced by violence, or indeed by any necessity.[11]

St Thomas establishes that acts which proceed on account of force are involuntary.[12]

St Thomas establishes that fear itself does not absolutely deprive an act of its voluntary character.[13]

These propositions are necessary for St Thomas to establish for the sake of the analysis of moral acts which are done ‘under duress’: how much ‘duress’ is enough to deprive a moral act of its voluntary nature and the agent of moral—and, in St Thomas’ world, legal—responsibility?

St Thomas establishes that concupiscence (in our terminology, desire) does not cause an act to be involuntary.[14] This is of course necessary to his analysis of moral responsibility where sins of the flesh are involved. However, this remark is to be considered in the light of St Thomas’ remarks, referred to above, where St Thomas establishes that when a passion overwhelms a man, then his reason is incapacitated.

St Thomas establishes that ignorance causes a sort of involuntariness in our actions.[15]

St Thomas then proceeds to establish that the circumstances of an act—here St Thomas follows both Aristotle and Cicero, the Stoic rhetorician—are important elements in the theological evaluation of the act.[16] He then enumerates the circumstances: the author of the act, where, with what assistance and with what instruments, why, how, when and what actually was done. Of these, St Thomas says, the most important are why the act was done and those things in which was the actual practice of the act. This is a very legalistic approach to moral theology: these circumstances are no different from the criteria in law for the evaluation of a justiciable act.

St Thomas establishes that the will tends only to the good. In this he remarks that the will is a rational appetite. Every appetite has some good as its end. He writes:

The will is a certain rational appetite; however, there is no appetite except of the good. The reason for this is that an appetite is nothing other than a certain inclination towards something of him who has the appetite.

Let us interject a remark here. This is a very important definition for St Thomas’ psychology: the will is an appetite just as hunger or thirst are appetites. We might even say that the will is a hunger or thirst after the good.

However, nothing inclines except to something similar and appropriate. Therefore, since each thing is a certain good, as much it is being (ens) and substance (substantia), it is necessary that every inclination should be towards the good; and from that the Philosopher [Aristotle] says in the Ethics, I: ‘The good is what all desire.’

Let us interject another remark. Here we see the tautological nature of St Thomas’ definition of the will: every object is a good because it has being and substance; therefore every inclination of the will towards an object is towards the good. But does a man’s will necessarily tend towards the object because of the being and substance in it? St Thomas proceeds in this way so as to preserve Aristotle, but from the point of view of human psychology, his approach is arbitrary.

But it must be considered that because every inclination follows some form, the natural [i.e. vegetative] appetite follows the form existing in nature. However, the sensitive appetite, or even the intellectual appetite, which is called the will, follows the apprehended [i.e. perceived] form. Therefore, just as that to which the natural appetite tends is the good existing in a thing (in re), thus that to which the animal or voluntary appetite tends is the apprehended good. Therefore, that to which the will tends in something is not required to be the good truly in a thing (in rei veritate), but to be apprehended under the aspect of the good (in ratione boni). And for this reason the Philosopher [Aristotle] says, in II Physics, 31, that: ‘The end is the good or the apparent good.’[17]

What is St Thomas saying? First he gives a not very persuasive reason—every thing has being and substance, so it has some good—that every inclination of the will is towards the good. That is to lay the foundation for a very important assertion: ‘The good is what all desire.’ This is fundamental: the will is an appetite or desire or hunger after the good. It would be fruitless to approach St Thomas’ psychology without assimilating this basic point. The will is a sort of magnet which is attracted to the Beatific Vision, but which can be attracted to lesser goods. We have already seen, however, that in St Thomas’ doctrine, those lesser goods necessarily exist in a metaphysical relation of goodness to the Beatific Vision as to a final cause.

Next, in some very elliptical argumentation, St Thomas says the following: The natural (or, ‘vegetative’)[18] appetite follows the form existing in nature. The natural appetite is simply the appetite as regards those powers of the human soul such as nutrition, growth and reproduction that are found in the vegetative soul in the Aristotelian schema of the kinds of soul. Although the vegetative appetite inclines towards the good existing in a thing—say, the nutritional value of the food I eat—it is unconscious. For the vegetative soul operates at the level of the unconscious biochemical processes of the body. That is the significance of what St Thomas is about to say concerning the sensitive and intellectual appetites, that their ends must be apprehended or perceived.

St Thomas then goes on to say that the sensitive appetite—that which relates to the desire, whether for food or for sexual contact—is necessarily an appetite for something that is perceived: I must see the food to want it; the member of the opposite sex to want her or him. St Thomas then concludes that just as the natural or vegetative appetite follows the good actually existing in a thing—the food, whatever it might be, has some good in it since it actually exists and is food—the sensitive appetite, and even the will, inclines to the good that is apprehended. What St Thomas means is this: The natural vegetative functions of my soul seek after the good in the food I eat but unconsciously to me: I have no perception of my act of digesting the food I have eaten. However, to desire the food that is before me, I must perceive it as appetizing, and in order to will an end—say, to follow a healthy diet—I must understand that end as good. I must perceive the food as good food in order to want to eat it and I must understand the healthy diet as a good in order to will it. Of course, what St Thomas is driving at is that I might be deceived: the apple, say, might be a plastic display item; the diet which I understand to be good might be unhealthy. Hence his quotation from Aristotle: the end or object of the will is the good or the apparent good.

We remarked above that St Thomas’ doctrine that men will the good seemed to be psychologically arbitrary. Here we see him to say that men will the good as they apprehend it. Has he covered our objection? No. Tautologically, you can always produce an analysis that the man willed the good or the apparent good whatever it was he actually did.

It is well to remark here that what today we ordinarily consider hunger and sexual desire have elements that are subsumed both under the vegetative soul and under the animal or sensitive soul. That is, there are bodily functions related to nutrition, growth and reproduction which operate in man at the unconscious, biochemical level, including involuntary bodily movements related to hunger or to sexual desire. These are functions of the vegetative soul of man. But there are also functions related to nutrition, growth and reproduction which operate in man at the conscious level that depends on sense-perception and which therefore are subject in St Thomas’ doctrine to conscious control by the reason. These are functions of the animal or sensitive soul of man. In the present article, St Thomas is saying that the unconscious appetites of the vegetative soul automatically seek after the good in the thing, and that the objects of the conscious appetites of the animal or sensitive soul must be apprehended or perceived as good in order to be desired. Thus in the case either of hunger or of sexual desire, there are aspects which are unconscious, biochemical and automatic and there are aspects which are conscious, dependent on sense-perception and subject to the control of reason. Later we will see that St Thomas explicitly limits the conscious control of the reason over the members of the body to those members of the body which are subject to the animal or sensitive soul.[19]

For the researcher into artificial intelligence, the import of this article is that the circuitry which maintains the basic functions of the robot such as the supply of electrical current should be completely separate from the circuitry and programming which support the ‘conscious’ functions of the robot, including its appetitive and intellect subsystems. Of course, the vegetative subsystem will have to send a signal to the desire subsystem when the battery runs low so that the robot feels ‘hungry’.

St Thomas establishes that the will tends not only towards the end but also towards the means. He writes this:

‘Will’ is sometimes said to be the very power (potentia) by which we will; sometimes, however, it is said to be the act of the will itself. If, therefore, we speak of ‘will’ in accordance with its naming the power (potentia), then it extends itself to the end and to the things which are towards the end. For every power (potentia) extends itself to those things in which the nature (ratio) of its object can in some manner be encountered, just as vision extends itself to all things of whatever sort that participate in some manner in colour. However, the nature (ratio) If, however, we speak of ‘will’ in accordance with its properly naming the act, then properly it is necessary to speak that much of the end. For every act denominated from a power names the simple act of that power, as ‘to cognize (intelligere)’ names the simple act of the intellect (intellectus). However, the simple act of a power is in that which is according to itself the object of the power; that, however, which on account of itself is good and willed is the end. Whence the will [where ‘will’ is here taken to refer to the power of the will] is properly of the end. Those things which are towards the end are not good or willed on account of themselves, but out of an ordering towards the end: whence the will is not carried towards them except to the extent they are carried towards the end, whence that itself which is willed in them is the end. And thus ‘to cognize (intelligere)’ is properly of those things which according to themselves are known, that is to say, of the [first] principles; however, it is not said of those things which are known through the [first] principles that they are cognized, except inasmuch as the [first] principles themselves are considered in them. For just as the end has itself in things which can be desired (appetibilibus), thus the [first] principle has itself in things which can be cognized (intelligibilibus). of the good (which is the object of the power of the will), is encountered not only in the end, but even in those things which are towards the end.[20]

What St Thomas is saying in this difficult but important passage is that a power such as the intellect or the will has as its object both those things with which it works directly and those things through which it works indirectly. However, the simple act of the power, named from the power by the use, in Latin, of the infinitive related to the noun that names the power or even by the use of the same noun, has as its object only that with which the power works directly. Thus ‘intellect’, taken as a power, has as its object the first principles—for example, the law of the excluded middle—and all the things in which the first principles are to be found. Similarly, ‘will’, taken as a power, has as its object the end and all the means to the end. However, ‘intellect’, taken as the simple act of the intellect, the simple or primitive act of cognition, has only the first principles as its object. Similarly, ‘will’, taken as the simple act of the will, the primitive act of willing, has only the end as its object.

In regard to artificial intelligence, we here see another indication how to proceed: The intellect subsystem will deal only with logical evaluation, arithmetic computation and such-like. When it is operating, the intellect subsystem will occupy itself only with the computation of a logical or arithmetic result. The will subsystem, however, will deal only with ends and means to attain those ends, and those only insofar as it puts ends and means into place as actual goals that the robot will work to achieve. Moreover, when the will subsystem is operating, it will operate only to secure the actual accomplishment of a goal, which of course itself might be the means to some end. We will see that the goal is evaluated by the intellect subsystem and adopted by the will subsystem after it has been communicated to it by the intellect subsystem.

St Thomas establishes that the will does not tend towards the end and towards the means to the end with one and the same act.[21] This is important for St Thomas to establish so that he can separate the willing of the end from the willing of the means: he must account for the choice of one means over another in view of a single end.

In artificial intelligence, the significance is that the designer of the robot must separate the programming in the will subsystem that relates to the adoption of the end from the programming in the will subsystem that relates to the adoption of the means to the end. But it is well to bear in mind that there can be a hierarchy of ends and means, so that a means as seen from the point of view of its related end can be seen as an end from the point of view of its own means.

St Thomas establishes that the will is moved by the intellect. St Thomas explains that the intellect moves the will in presenting to it its object. That is, the intellect selects the object or end that the will adopts. This is an important move in St Thomas’ analysis. The will is a hunger and thirst after the good, but it is the intellect, the reason, which presents it with the good after which it will hunger. St Thomas says this:

As much as something has need of being moved by something else, by that much it is in potency (potentia) towards more things; for it is necessary that that which is in potency (potentia) be reduced to act (actus) by something which is in act, and this is ‘to move’. However, a certain power of the soul comes to be in potency (potentia) in regard to various things in two ways: in one way, as much as it can do or not do; in the other way, as much as it can do this or that—just as the sight sometimes sees in act, and sometimes does not see; and sometimes it sees white and sometimes it sees black. It therefore has need of being moved as much towards the two, that is to say, as much towards the exercise or the use of the act, and as much towards the determination of the act: the first of these is on the part of the subject, which sometimes comes to be doing and sometimes not to be doing; however, the other is that which is on the part of the object according to which the act is specified; however the motion of the subject itself is from some agent. And as every agent acts on account of an end, as has been demonstrated,[22] the principle of this movement is from the end. And in that is why the art to which pertains the end moves by its command the art to which pertains that which is towards the end: just as the navigational art commands the art of shipbuilding, as is said [by Aristotle] in II Physics, 25. However, good in general, which has the nature (rationem) of the end, is the object of the will; and on account of this the will on its part moves the other powers (potentia) of the soul to their acts; for we make use of the other powers when we will. For the ends and the perfections of all the other powers are included under the object of the will as particular goods of a sort. However, the art or power to which pertains the universal end always moves to action the art or power to which pertains the particular end contained by that universal end. Thus the leader of the army, who intends the common good, that is to say, the order of the whole army, moves by his command some one of the tribunes, who intends the order of one of the units. But the object [of the act] moves by determining the act in the sense of the formal principle by which in natural things the action is specified, just as [the act of] heating is [specified] by heat [i.e. the formal principle ‘heat’ specifies the act ‘heating’]. However the first formal principle is being (ens) and universal truth, which are the object of the intellect; and on account of this, the motion of the intellect moves the will in this manner, as presenting to it its object.[23]

What this means is that, first, according to Aristotelian metaphysics, for a power of the soul to pass from potentiality to actualization, it must be moved by something. But this motion, or change, is to be taken in two senses: In the first sense, the power can be exercised or not. This is a matter of the subject, of the power itself. In the second sense, the power is moved in that it is determined by its object: once I see, the content of my sight is determined by what I actually see: the object might be white or black, and that object determines the content of my sight. Similarly, I may will or not will, but once I will, the content of my willing is determined by what I will: my object or my end or my goal. However, in the case of the powers of the soul other than the will, it is the will, whose object is the good, that moves them to exercise their power. The will commands them, just as the general commands his lieutenants. However, it is the intellect that presents to the will its goal.

This relation of the will to all the other powers of the soul—it moves them to the exercise of their power—and of the intellect to the will—it presents the will with its object—is very important to St Thomas’ analysis. It is the heart of his theory of human action.

Let us remark here that the notion of ‘moving’ something is a technical term in Aristotelian metaphysics. It simply means that if something moves something else, then it causes it to act: it causes it to pass from potentiality to actualization. But in Aristotelian metaphysics, causes can be final: when I will an end, then it is as final cause that that end moves my will in determining its content. It would be fruitless to try to analyse this notion in terms of modern theories of causation. It simply means that the object of my willing is my goal and that the content of my willing has been determined by that goal taken as goal.

Next, St Thomas is establishing an order among the powers of the soul. First is the intellect, which presents to the will its object. Then the will moves the other powers of the soul to action, as a general commands his inferior officers. The will can even move the intellect. But higher than the will is the intellect, which presents to the will its end. This is a hierarchy of powers of the soul. It is fundamental to St Thomas’ model of human action.

It should be noted that in St Thomas’ doctrine, the relationship between the intellect and the will is strongly and explicitly reciprocal: the will can set the intellect in motion, as when by an act of the will we set about learning mathematics; more importantly, for the intellect to give the will its command, the intellect must previously have been set in motion by the will.

In artificial intelligence, what we can take from this, if we treat the powers of the soul as separate subsystems of the robot, is that there is a hierarchical relation among the subsystems: the will is the executive subsystem which issues commands to all the other subsystems. However, the will subsystem receives its goal from the intellect subsystem. Moreover, there is an interactive relationship between the will subsystem and the intellect subsystem: the one can put the other into operation. St Thomas has provided the researcher into artificial intelligence with a model of the internal logical organization of a robot.

Let us now look at the notion of ‘subject’ in what St Thomas has said. He cannot mean that there is a ‘subject’, a person, behind the will that is pushing the will to will: that would involve him in an infinite regression of wills and subjects. However, he has to account for the fact that in Aristotelian metaphysics, something that comes to be in act that was not in act has to be moved by something else to the exercise of that act. A power of the soul that was not in act has to be moved by something in order to pass from potentiality to act.

For the lesser powers of the soul, St Thomas has no problem: the will moves them to act.

For the intellect, the matter is somewhat more ambiguous, for the will can move the intellect, and must move it, in order for the intellect later to command the will. However, since it is the intellect which commands the will, or, here, presents to the will its object, how do things start off? How is it that the will itself is originally moved to act on the intellect? St Thomas later posits that the only external cause that can move the will is God himself, and that not in a necessary way.

While later St Thomas asserts that the will can cause itself to will, he both restricts that notion and interposes an act of the intellect.

The problem is this: St Thomas is faced with providing causal explanations for human action at the level of the mutual relations of powers of the soul, within the Aristotelian metaphysics of the four causes. But he runs up against the irreducible freedom of man: a man acts. There is a tendency discernible in St Thomas’ analysis of human action to avoid the fundamental reality of human freedom. For each power of the soul is set in motion by another power of the soul, at the risk of losing the person who acts freely.

In artificial intelligence, the problem is succinctly put: the designer must avoid a situation in which the will subsystem is eternally waiting to be put into motion by the intellect subsystem while the intellect subsystem is eternally waiting to be put into motion by the will subsystem. Things have to get a start somewhere. We would suggest that the designer start them off in the will subsystem. He should design the will subsystem to operate cyclically so that every so often it puts the intellect subsystem into action to see how things are and to present any goals that it might discover based on an evaluation of possible ends, especially in view of data from the perceptual and vegetative subsystems. However, the difference between a robot and a merely automatic machine is that in a robot things do not depend merely on the perceptual subsystems: in the robot, the will and the intellect subsystems together constitute a principle of autonomous action: the robot can by itself, independently of sensory input, decide what to do.

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[1] ST Ia IIae, 6, 1.

[2] Ibid.

[3] ST Ia IIae, 6, 2.

[4] Ibid.

[5] ST Ia IIae, 10, 3, quoted below.

[6] ST Ia IIae, 6, 2.

[7] In ST Ia IIae, 10, 3.

[8] ST Ia IIae, 6, 2, ad 1.

[9] ST Ia IIae, 6, 3.

[10] Bourke pp. 223–25.

[11] ST Ia IIae, 6, 4.

[12] ST Ia IIae, 6, 5.

[13] ST Ia IIae, 6, 6.

[14] ST Ia IIae, 6, 7.

[15] ST Ia IIae, 6, 8.

[16] ST Ia IIae, 7.

[17] ST Ia IIae, 8, 1.

[18] ST Ia IIae, 17, 8.

[19] ST Ia IIae, 17, 9.

[20] ST Ia IIae, 8, 2.

[21] ST Ia IIae, 8, 3.

[22] ST Ia IIae, 1, 2.

[23] ST Ia IIae, 9, 1.


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