Chapter 1: Must be studied because (a) reason prescribes the mean,(b) they are a part of human excellence. The intellect is (1) scientific, (2) calculative: we want the virtue of each.

We said above that what we should choose is neither too much nor too little, but “the mean,” and that “the mean” is what “right reason” prescribes. This we now have to explain.

Each of the virtues we have discussed implies (as every mental habit implies) some aim which the rational man keeps in view when he is regulating his efforts; in other words, there must be some standard for determining the several modes of moderation, which we say lie between excess and deficiency, and are in accordance with “right reason.” But though this is quite true, it is not sufficiently precise. In any kind of occupation which can be reduced to rational principles, it is quite true to say that we must brace ourselves up and relax ourselves neither too much nor too little, but “in moderation,” “as right reason orders;” but this alone would not tell one much; e.g. a man would hardly learn how to treat a case by being told to treat it as the art of medicine prescribes, and as one versed in that art would treat it.

So in the case of mental habits or types of character also it is not enough that the rule we have laid down is correct; we need further to know precisely what this right reason is, and what is the standard which it affords.

The virtues or excellences of the mind or soul, it will be remembered, we divided into two classes, and called the one moral and the other intellectual. The moral excellences or virtues we have already discussed in detail; let us now examine the other class, the intellectual excellences, after some preliminary remarks about the soul.

We said before that the soul consists of two parts, the rational and the irrational part. We will now make a similar division of the former, and will assume that there are two rational faculties: (1) that by which we know those things that depend on invariable principles, (2) that by which we know those things that are variable. For to generically different objects must correspond generically different faculties, if, as we hold, it is in virtue of some kind of likeness or kinship with their objects that our faculties are able to know them.

Let us call the former the scientific or demonstrative, the latter the calculative or deliberative faculty. For to deliberate is the same as to calculate, and no one deliberates about things that are invariable. One division then of the rational faculty may be fairly called the calculative faculty.

Our problem, then, is to find what each of these faculties becomes in its full development, or in its best state; for that will be its excellence or virtue.

But its excellence will bear direct reference to its proper function.