Aquinas' ethics is constructed as a practical study (scientia practica): it is an organised type of knowledge leading to certain general judgements about what is right or wrong in human activity. Its development starts with experience of the ordinary facts of human living, plus some insight into interpretive principles. As such, Thomistic ethics does not deal directly with individual particular actions (this is the sphere of personal prudential judgement and conscience). Rather, this ethics is concerned with general practices (such as giving to the needy, controlling one's excessive emotions, procreating offspring, stealing, homicide, and so on). Since it is universal in its conclusions (a requirement of Aristotelian 'science', episteme, scientia), Thomistic ethics is designed to be teachable. An ethics that attempts to judge individual deeds is not considered communicable because it is trying to judge private decisions.

One basic characteristic of this sort of ethics is its stress on ends or goals of human activity (ST I-II, q. 1, 1-8 InS II, d. 40, 1; Vir art. 2, ad 3m; CG III, 2; EE I, lect. 2). As a teleological study this ethics judges various types of action in terms of the end-directed character of human nature. For a person to be reasonable involves acting well for some intended purpose; conversely, unreasonable human action is either without conscious purpose, or it employs means not calculated to achieve a properly intended end. In a very broad sense a morally good action is one consciously chosen on the basis of honest thinking about its suitability to achieve an appropriate goal. This teleological orientation does not imply that a good end justifies the use of merely any means that will work (ST I-II, q. 18, 4 6). Aquinas recognised the importance of the moral agent's prior attitude (intelligent thinking, reasonable willing, controlled emotions) as well as attention to the consequences of one's moral actions to self and society.

Thomistic moral psychology focuses on three distinctively human functions (ST I, qq. 75-88). He accepted the ancient definition of man as a rational animal but reinterpreted it in terms of intelligence, volition and emotion (ST I-II, qq. 8-17). Most characteristic of man is his intellect: this includes the ability to understand the universal meanings (rationes, intelligibilities) of the facts of sense experience, and the further ability to reason to theoretical and practical conclusions entailed in the comprehension of such experience. In the second place, human understanding provides a stimulus for positive or negative will-acts in regard to what is understood. It is, for instance, one thing to understand the meaning of peace, and quite another thing to will to do something about it.

Apart from sensory appetition (emotional and affective responses to individual aspects of sense objects), there is a higher level of appetitive response (pro or con) to what is grasped intellectually as a universal good or evil. Thus one may desire to drink some orange juice, because it tastes good (sense appetite) and/or because it is understood to promote good health (intellectual appetite, will). Volition (from the Latin for will, voluntas) is quite different from passion, emotion, sensory affectivity. One wills for a universal reason but one feels affectively as a response to quite particular attractions or repulsions of sensed objects.

Intellectual and volitional functions play a key role in the exercise of personal freedom. Choice and the direction of one's moral actions depend on prior considerations that are both cognitive and volitive...

... man is envisioned as thinking and willing, first of all, about some sort of goal. One might consider, for example, how good it would be to live forever. But then one would usually realise that this is not possible. Cognitively these thoughts reduce to the apprehension of the meaning of this end and the judgement that it is not attainable. Volitionally one might briefly wish never to die then with the realisation that this objective is impossible one would will to reject it. Such rejection terminates the considerahon in this case but an end judged to be possible may lead to positive adoption (intention). It is not that intellect and will are viewed as two separate agencies but rather that the whole person is the agent who must both judge various goals and adopt or reject them willingly.

If one decides that a certain end is attainable (say, for example, getting a better education), then practical consideration turns next to the things that may be done (the means) to attain this end which has been judged possible and which one intends to achieve. Think of a farm boy who would like to go to college. He may weigh (the literal meaning of deliberation) the various means that he might use: ask his skinflint father to pay his tuition, get his rich aunt to help him, or work for a while as a hired hand to raise the money. If he decides on the last means, he may then willingly adopt it (consent to the means) as the best available thing to do. However, this need not lead to immediate bodily action: the young man may judge that it would be better to wait a few years and help his father on the farm. But if he decides intellectually (the judgement of choice) that it is better to start to work right away on his paying job, then he may elect willingly to do this (the choice act). At this point personal freedom is most evident both in his understanding of the situation and in his willing commitment to the means. Such choices usually entail further implementation by carrying out either bodily or mental actions (commanded acts) under the guidance of such intellection and volition. Clearly, too, one's emotions are involved throughout such decisions but not, in a rational agent, to the extent of dominating the process. In this area of execution, the understanding of how the proposed external act must be ordered is called command but the actual translation of such thinking into deeds is named use. One must finally will to do it, or not. The physical and mental activity involved in working and saving the tuition money may be a lengthy commanded action, done as a result of prior understanding, judging and willing that it must be done. At any point in the implementing of one's choice, it is possible to decide for or against the appropriateness of the commanded act. If the young man realises eventually that his savings will never enable him to go to college, he may terminate his efforts. But if he decides that he is doing well and may have enough money to start college next year, then he approves his work, so far, and enjoys a certain satisfaction (fruition) in his accomplishment.

The foregoing 12 steps are parts of a schematic analysis: one does not usually go through such a process of moral consideration in such detailed fashion. The point of the analysis is not that one must think: now I am adopting my objective, now I am selecting appropriate means, and now I am ordering myself to use or enjoy a given deed. Rather, the intellective-volitive analysis can be valuable, if there is some failure to act reasonably. Just as the person who has lost the ability to walk or talk properly may have to consider the various steps involved in such apparently simple functions, so may the moral agent (or his adviser) need to break down his unsuccessful moral action into the various points at which his failure to think or will properly might be corrected.

Thomistic moral psychology also places much stress on habit formation. Three kinds of conscious powers are regarded as capable of development by the acquisition of permanent dispositions or habits (habitue). These powers are capacities flexible enough and free enough to be improved by appropriate usage. Intellect, will and emotive capacity are of this type. Intellectual understanding may become more proficient with use: some trained people can solve difficult mathematical problems and untrained ones cannot. Aristotle taught that there are five distinctive intellectual habits (hexeis): the ability to grasp the starting-points (principles, definitions) of reasoning; the skill to reason step-by-step to well-established conclusions (episteme, scientia, scientific thinking); the ability to evaluate one's experience in terms of the highest standards (sophia, wisdom); the acquired ability to reason to good practical conclusions concerning one's free actions (phronesis, prudence, practical wisdom); and finally, the acquired ability to make things reasonably well (poiesis, art). Thomas Aquinas adopted much of this Aristotelian teaching on intellectual habits and he particularly emphasised the ethical importance of the primary intuition of first practical principles by the intellectual habit of synderesis.

... the role of synderesis was not to provide man with an insight into detailed moral standards, or special rules of behaviour. What Aquinas thought was that, just as theoretical reasoning begins with certain initial axioms (such as the principles of non-contradiction or of identity) which are not demonstrable but are grasped by natural insight, so in practical reasoning there are primary indemonstrable principles (such as, good is to be done and evil avoided, or, no harm should be done to others). If their terms are understood, these are intellectually self-evident. More specific ethical judgements are made, Thomas thought, in the light of such guiding principles but with a content supplied by further experience of life (DV XVI, 1 and 2; ST I-II, 94, 1). For example, one might readily subscribe to the general principle that harm should not be done to others. On the other hand, it may not be obvious, usually and in the first instance, that cheating on one's just taxes would be a case of violating this principle.

The power of willing (intellectual appetite) was viewed by Aquinas as able to be actualised (perfected) by many habits. The repeated practice of diligent study, a regular tending of the sick or frequent efforts to assist the poor would all dispose one to perform such actions with increased ease and desire. Correspondingly, constant cheating, Iying, excessive drinking or eating would readily dispose one to perform such actions with greater and greater ease and desire. Such actions, reasoned as desirable for one, become crystallised as habits.

The chief naturally acquired habit of will he called justice: the virtue of willing and doing what is good for others, as for one's self. The reason why such altruism is rooted in willing lies in Aquinas' view that the good of other persons is always a somewhat abstract and universal object, as compared with one's own concrete advantage. He discussed many kinds of justice and lesser virtues associated with it (ST II­II, qq. 57-122). However, Thomas saw the great importance of another will-habit that was almost unknown to Aristotle. This is charity (caritas), the habit of loving other persons as special creatures that God has made. This sort of divinely-motivated love is called a theological virtue. As far as Thomistic ethics is concerned, it is much more important than justice. Of course, even Aristotle saw that the 'love of friendship' values the other person and his/her good for its own sake, and so for something more than one's own private advantage. This aspect of justice is an approach on the natural level to the level of supernatural charity. In Aquinas' teaching charity is the 'form' of all moral virtues: it gives an essential and superior character of excellence to the well-developed moral person.

In the sphere of emotional responses (sensory appetition) Thomas distinguished two different general types: the sort of feelings that culminate in sensory desires (concupiscible appetites) and the affective reactions to various difficulties and threats presented in sensory experience (irascible appetites). Desires for food, intoxicants and sexual pleasure tend to become excessive (sometimes defective) and the habit of moderation in such matters is temperance. It is developed in the concupiscible appetite under the regulation of intellect and will. The notion of the golden mean between excess and defect of feeling is incorporated from ancient classical ethics into Aquinas' account of temperance. Besides the major species of habitual moderation in regard to food, intoxicants and sexual pleasure, many other forms of reasonable self-control are studied in his treatises on the virtues. The influence of Stoicism as well as Aristotelianism is evident in these discussions of moral moderation.

A quite different field of human emotions (passiones animae) is associated with movements of the irascible appetite (DV XXV, 2; DM VIII, 3; ST I, 81, 2 and 3). This power is the seat of feelings such as hope and despair, daring and fear and the complex emotion of anger. The chief problem that Thomas saw here was man's tendency to submit weakly to various attacks on his well-being. So fortitude (emotional strength) is the primary good habit in this area. It is a virtue which enables one to bear up courageously, when the tendency is to despair about some perceived evil, and to attack and overcome such threats, when they seem reasonably open to such positive action (InJ, passim). Here again Stoic ethics had an impact but Aquinas broadens his treatment of these emergency passions to include many habits of courage in regard to dangers both physical and spiritual.

From the foregoing it may become clear that this moral psychology is an essential basis for all other themes in Thomistic ethics. It has ramifications in Thomas' treatment of freedom and voluntarism, in the explanation of moral law in terms of inclinations, and indeed of almost every aspect of his moral philosophy. Since this psychology leads to a study of hundreds of moral virtues and vices, Thomism might well be named an aretaic ethics for it is an ethics of self-perfection through the growth of many virtues.