In order to do what is virtuous one must act in accordance with right reason. It is therefore necessary to specify what right reason is.
It was previously stated that some virtues are ethical and others intellectual. Now that we have discussed the ethical virtues, we will move on to the intellectual virtues. There are two parts of the soul, one rational and one nonrational. We can further subdivide the rational part into that by which we perceive unchanging principles and that by which we investigate things that vary. The first of these we call the scientific' part and the other the estimative' or deliberative' part, because we don't deliberate about unchanging things.
Three parts of the soul have authority over action: sense, intellect (or intuition) and desire. Sense is not a principle of action. For the intention to be right in an action reason needs to be correct and the desire has to be in accordance with right reason. In addition it is necessary to form an ethical habit in order to acquire the actual virtue. Intention is either "desiring intellect" or "thinking desire," and this is the principle of man, since man is defined mainly by his intellect. Both rational parts of the soul are ordered to truth.
There are five things by which the soul may possess truth: art, knowledge (scientific), prudence, wisdom and intuition. Something which is an object of knowledge exists of necessity and is therefore eternal. First principles are acquired by induction.
Art is concerned with bringing something into existence. To think by art is to investigate how to generate something which may or may not exist. Art is concerned with production, not with action.
Those whom we call prudent deliberate well about what is good and advantageous to themselves and about life as a whole. One doesn't deliberate about things which are unchanging or which are not in one's power to do. Therefore prudence can't be scientific knowledge or an art. Prudence is a disposition with true reason and ability for actions concerning human goods. The word for temperance is derived from the word for prudence (in Greek). Prudence is the virtue of that part of the soul which can form opinions.
Scientific knowledge is universal and necessary and what is scientifically known is demonstrable, while art and prudence are changing.
Wisdom is the most accurate of all the sciences. The wise man must know both what follows from the principles but also possess truth about the principles. What is wise is always the same while what is prudent is changing; thus wisdom is superior to prudence in dignity.
Prudence is concerned with the human good; it is not limited to what is universal but must also know the particulars, for it is practical. For prudence, particulars are more important than universals because prudence is related to action. Prudence is generally concerned with individual matters, but other types are financial management, legislative prudence and political prudence.
Prudence takes time to acquire because it is learned from experience. Prudence is opposed to intuition, for intuition regards definitions for which one doesn't deliberate.
Deliberation is a type of inquiry. Good deliberation is rightness of thinking. Good deliberation means not only that instrumental reasoning of figuring out the means to attain a certain end, but it must also have a good end in view and been done in the proper way and at the proper time.
Intelligence is concerned with the same kind of object as prudence, but is not the same. Prudence gives orders with regard to what should or should not be done, but intelligence judges. Good judgment is the right judgment of an equitable man.
All these faculties are concerned with the same things as prudence. By nature man has judgment, intelligence and intuition.
Wisdom and prudence are worthy of choice for their own sake, because they are each a virtue of the corresponding part of the soul. As a part of the whole of virtue, wisdom produces happiness by its exercise. A man's work is completed both prudence and ethical virtue. For virtue makes the end right while prudence makes the means right. To be good a man must act by intention and for the sake of the things done.
Cleverness or shrewdness enables us to act successfully upon the means leading to an end. It presupposes and end the nobility of the end determines the goodness of it. For a man who is not good, the correct end may not be apparent because bad habit may corrupt him. A man cannot be prudent if he is not good. However, without prudence there is no virtue. When prudence exists in the complete sense, all the other virtues are present.
Some people are naturally virtuous and desire good ends. The greatest natural virtue is wisdom.
The virtue which one must develop in order to attain moral virtue and to find the correct mean in all of one's actions is prudence. Prudence is the ability to deliberate well regarding human actions. Concerned with particulars of action, prudence is absolutely necessary in order to find the mean, or in Aristotle's words, "to know what is good for oneself" (1142a). The philosopher even goes so far as to say that "without prudence virtues cannot exist," but that where there is prudence, "all the others are present" (1144b). Prudence and ethical virtue are in fact inseparable, much like two sides of the same coin, "for while virtue makes the end in view right, prudence makes the means towards it right" (1144a).
To acquire ethical virtue, several conditions are necessary: (1) the good must be known, (2) one must deliberate properly to seek the means for it through reason, (3) one must intend to do the good for its own sake, (4) one must desire to do what is good, and (5) virtuous action must be repeated to produce a habit.
It seems, however, that by connecting prudence and ethical virtue so closely, Aristotle has created a closed circle which precludes one from becoming virtuous. Prudence concerns means, not ends. The correct end is presupposed. But the ends themselves seem to require prudence. In stating that "a man cannot be good in the main sense without prudence, nor can he be prudent without ethical virtue," Aristotle seems to present a "chicken and egg" paradox: one cannot become prudent without the experiences of virtuous action, yet one cannot be virtuous without prudence. Perhaps the answer to this paradox is that virtuous habits can be acquired little by little through proper education and obedience to just laws. Those habits give rise to a certain amount of prudence which then allows the person to be more virtuous and so on. Thus the relationship between ethical virtue and prudence can best be characterized as an inward spiral which little by little reaches the center, which is a virtuous life.
Wisdom is connected to prudence as health is to medicine. Wisdom is the superior of the two, and prudence is a means to wisdom as medicine is a means to health. The prudent man considers how wisdom is acquired and prescribes his actions in order to acquire it.