• Nicomachean Ethics 1106a25
• In everything that is continuous and divisible it is possible to take more, less, or an equal amount, and that either in terms of the thing itself or relatively to us; and the equal is an intermediate between excess and defect. By the intermediate in the object I mean that which is equidistant from each of the extremes, which is one and the same for all men; by the intermediate relatively to us that which is neither too much nor too little---and this is not one, nor the same for all. For instance, if ten is many and two is few, six is intermediate, taken in terms of the object; for it exceeds and is exceeded by an equal amount; this is intermediate according to arithmetical proportion. But the intermediate relatively to us is not to be taken so; if ten pounds are too much for a particular person to eat and two too little, it does not follow that the trainer will order six pounds; for this also is perhaps too much for the person who is to take it, or too little--too little for Milo, too much for the beginner in athletic exercises. The same is true of running and wrestling. Thus a master of any art avoids excess and defect, but seeks the intermediate and chooses this--the intermediate not in the object but relatively to us.
• If it is thus, then, that every art does its work well--by looking to the intermediate and judging its works by this standard (so that we often say of good works of the art that it is not possible either to take away or to add anything, implying that excess and defect destroy the goodness of works of art, while the mean preserves it; and good artists, as we say, look to this in their work), and if, further, excellence is more exact and better than any art, as nature also is, then it must have the quality of aiming at the intermediate. I mean moral excellence; for it is this that is concerned with passions and actions, and in these there is excess, defect, and the intermediate. For instance both fear and confidence and appetite and anger and pity and in general pleasure and pain may be felt both too much and too little, and in both cases not well; but to feel them at the right times, with reference to the right objects, towards the right people, with the right aim, and in the right way, is what is both intermediate and best, and this is characteristic of excellence. Similarly with regard to actions also there is excess, defect, and the intermediate. Now excellence is concerned with passions and actions, in which excess is a form of failure, and so is defect, while the intermediate is praised and is a form of success; and both these things are characteristic of excellence. Therefore excellence is a kind of mean, since it aims at what is intermediate.
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• Excellence, then, is a state concerned with choice, lying in a mean relative to us, thus being determined by reason and in the way in which the man of practical wisdom would determine it. Now it is a mean between two vices, that which depends on excess and that which depends on defect; and again it is a mean because the vices respectively fall short of or exceed what is right in both passions and actions, while excellence both finds and chooses that which is intermediate....
• But not every action nor every passion admits of a mean; for some have names that already imply badness, e.g. spite, shamelessness, envy, and in the case of actions adultery, theft, murder; for all of these and suchlike things imply by their names that they are themselves bad, and not the excesses or deficiencies of them....