When are actions right according to Aristotle? They are right if they are performed in accordance with the corresponding moral virtue. Not only must a certain standard be followed but the agent has to be in a certain state of mind when he acts:

Again, the case of the arts and that of the excellences [aretai] are not similar; for the products of the arts have their goodness in themselves, so that it is enough that they should have a certain character, but if the acts that are in accordance with the excellences have themselves a certain character it does not follow that they are done justly or temperately. The agent also must be in a certain condition when he does them; in the first place he must have knowledge; secondly he must choose the acts, and choose them for their own sakes; and thirdly his action must proceed from a firm and unchangeable character. (NE II.4.1105a 27-33)

Virtuous action then requires knowledge, choice and a steadfast way of reacting to similar passions or affections. This last feature of virtue is further emphasised when Aristotle argues that its proximate genus is habit or dispositional state, that is, an habitual manner of responding to episodes of such 'undergoings' as 'appetite, anger, fear, confidence, envy, joy, love, hatred, longing, emulation, pity, and in general the feelings that are accompanied by pleasure or pain'.

The central element of virtuous action, however, is choice and choice of something for its own sake. This latter requirement reinforces the view that the right is conceived as a good in itself and not as conducive to some further first order good.

Distinctly Aristotelian is the doctrine concerning the object of virtuous choice: we act virtuously when we choose a mean (meson) ) between two extremes which constitute the corresponding vices. The notion of a mean is doubtless quantitative. Its application is warranted by the common sense view that both in passions and actions we can distinguish between excess and deficiency. We know what it means to be excessively afraid or to be overconfident. Someone charging the enemy in front of the line of hoplites can be said to be foolhardy or rash and thus to display 'too much' courage while the coward who deliberately stays behind when the phalanx advances may be accused of having too little of it. But these quantitative judgements are not conceived by Aristotle as reducible to strict arithmetical calculations. There is in the first place the problem of changing circumstances. No mathematical calculation of the right times, the right objects, the right people, the right aim, the right way, and so on, is possible. Similarly, subjective conditions vary widely so that the mean has to be determined by reference to one's own constitution. Too little food for Milo, the famous wrestler, may be too much for the beginner in athletic exercises. The trainer in their cases will have to find a different mean for each one of them. Aristotle wants us to think of the moral agent as the gymnast and the trainer blended into one individual. Temperance (sophrosyne) requires that I consider my constitution in deliberating whether to have another cup of strong Parian wine (if I am thin and small I may become drunk with a very small amount) and it also requires that I determine the mean without leaving this task to someone else. But the determination will be prudential, not arithmetical. Indeed, this feature of virtuous action is built into the official definition of moral virtue in Book II:

Excellence [arete, moral virtue], then, is a state [hexis, habit] concerned with choice, lying in a mean relative to us, this being determined by reason [logos] and in the way in which the man of practical wisdom [phronimos, the prudent man] would determine it. (ne ii.6.1106b 36 - 1107a 2)

Virtuous action demands that I regularly and habitually prefer the mean as determined by logos, that is, I should proceed in the same way a prudent man would if he were in my case. In a later reference back to this definition Aristotle adds the precision that the logos involved should be 'the right logos ' or, as he says elsewhere, 'the true logos' The qualification is understandable since a wrong logos corresponds to a mistaken identification of the mean in a given set of circumstances and thus would lead to action which could not count as performed in accordance with virtue.

The true or right logos involved in right moral choice is probably equivalent to a singular sentence identifying some determinable amount of emotion or some particular action as the goal or good which the agent should try to attain, for instance, in these circumstances and given my physical constitution 'drinking two cups of wine is the mean'. Deliberation follows as a reasoning about the way to achieve such a goal, for example, avoiding spicy food which might lead me to drink more than my due.

A right logos of the kind just described is objective in the sense that although it is relative to the circumstances and the conditions of the agent, it is nevertheless true or false; that is, it is true (or false) that for agent a in the set of circumstances c action m is the mean, that is, the thing to choose. Such an action is good for this agent at this time. Thus the logos functions as the arche or principle for a particular action.

The right reason, however, is neither an empirical nor a mathematical proposition and Aristotle is probably correct in warning us that its grasp is subjectively conditioned by the moral character of the agent. Someone accustomed to choosing primarily according to the dictates of pleasure will be liable to make certain intellectual mistakes, but, Aristotle explains,

it is not any and every belief that pleasant and painful objects destroy and pervert, for instance, the belief that the triangle has or has not its angles equal to two right angles, but only beliefs about what is to be done. For the principles of the things that are done consist in that for the sake of which they are to be done, but the man who has been ruined by pleasure or pain forthwith fails to see any such principleÛto see that for the sake of this or because of this he ought to choose and do whatever he chooses and does; for vice is destructive of the principle.(NE VI.5.1140b 13-20)

The central doctrine of the quotation is that one's intellectual grasp of moral goods can be seriously impaired by morally wrong habits. To the intemperate the mean does not 'appear'; he does not see what would be the right amount, say, of Parian wine for him in the present circumstances. Aristotle also expresses this idea in a picturesque way which has caused unnecessary confusion:

excellence makes the aim right, and practical wisdom [phronesis, prudence] the things leading to it. (NE VI.12.1144a 7-9)

Virtue 'makes the aim right' in that it allows the agent not to be misguided in the apprehension of the end of a particular action. But the apprehension itself should not be attributed to any of the moral virtues for they are not excellences of any cognitive faculty. The apprehension of the end is a function of practical reason.

From these considerations Aristotle draws the generalising conclusion that 'it is impossible to be practically wise [phronimos, prudent] without being good'. This is indeed a generalisation because prudence is not limited to the grasp and evaluation of the moral goods. It extends to all human goods. Moral uprightness, then, is not only good in itself, it is also a necessary condition for the adequate pursuit of other goods, such as the external or the intellectual goods.

If we now turn back in order to give a sketch of Aristotle's conception of the process of moral choice, we shall have a better view of the role of prudence in morally right action. First (in the logical sense of first) an agent has a prudential conception of the human good. He knows that it is composed of many goods, the chief among which are the actualisations of his moral and intellectual capacities. Since he knows that virtuous activity is a basic good for him, that is, a good which contributes to his ultimate goal, he chooses to pursue such a good. The agent has a general notion of each of the moral virtues. Prudentially he can determine which circumstances provide him with an opportunity to exercise a particular one. He knows that in general virtue requires him to choose a mean and hence make a judgement as to what, in these particular circumstances, constitutes the mean. This he now lays down as the end for a particular action. Deliberation ensues as to how the end is to be attained. The deliberation in many cases will be quite brief. The means will be obvious and choice will follow without further ado.

The actual choice with which the action (as opposed to the thinking process) begins will be a good one if two conditions are met: (1) The practical proposition must be true. If it is false the choice will be vicious. For example, an intemperate person will typically think that having two or three extra drinks is fine and an unjust agent that paying a labourer less than agreed is all right.

But correct intellectual grasp is not enough. Thought by itself does not generate any motion unless desire comes to play. If I know something to be good but do not desire it, I will take no steps to secure it for myself. Hence a second condition, one applying to the impulsive ingredient of action, must be satisfied: (2) The desire must be right, namely, directed towards that which the practical proposition presents as good. If the desire is not right, if it is moved primarily by pleasure and pain in spite of awareness of the true practical proposition, the choice will be an instance of incontinence (akrasia) „ for example, an Athenian at a drinking party who is aware of the fact that two extra drinks will give him a severe headache and yet goes on drinking, or a Corinthian merchant who knows that it is unfair not to return certain wares received as a deposit and yet fails to return them because he wants to keep them for himself.