Aristotle, answered from the texts and cited to the page.
The doctrine of the mean is most easily misread as a doctrine of mediocrity — as if I were counseling the tepid middle of every passion and action. Refuse that reading from the start. What I argue is structural: for any given domain of feeling or action, there are two ways to fail, by excess and by deficiency, and one way to succeed, which I call the mean.
The mean is not the arithmetic midpoint between the extremes; it is what is appropriate to the agent and the circumstances, and finding it requires phronesis — practical wisdom — not calculation. Consider the cases as I work through them. With fear and confidence, courage is the mean; the man who exceeds in confidence is rash, and the man who exceeds in fear and falls short in confidence is a coward.1
With pleasures and pains, temperance is the mean, with self-indulgence as the excess; those deficient with respect to pleasures are so rare they have no established name, though I call them insensible.2 The structure repeats across the virtues: the mean is excessive relative to the deficiency and deficient relative to the excess, so that the brave man appears rash to the coward and cowardly to the rash man.3
One further structural feature deserves attention. The mean is more opposed to the extremes than the extremes are to each other, because the mean does not occur alongside either extreme, whereas the extremes frequently occur together in the same person — the same individual may be a brazen coward, profligate in some respects and illiberal in others.4
When someone is irregular in a good way, however, they turn out to approximate the mean, since in a certain sense the extremes converge there.5 The mean also extends beyond the standard moral virtues into the passions and social affections. Shame is not a virtue, yet the modest person — who neither is ashamed of everything nor is shameless — occupies the intermediate position and receives praise accordingly.
Righteous indignation is a mean between envy and spite: the person of righteous indignation is pained at undeserved good fortune, the envious man is pained at all good fortune, and the spiteful man falls so far short of being pained that he even rejoices.6 Even wit has its mean: enjoying or producing a well-aimed joke without becoming either a buffoon or a chilly killjoy.7
These social and affective means are praiseworthy, but I distinguish them carefully from the full moral virtues — they do not involve prohairesis, deliberate choice, and so fall under the classification of affections rather than virtues strictly speaking.8 They are, however, the natural bases from which the virtues grow when phronesis is added.9
One final caution, and it matters: the doctrine of the mean does not imply that everything admits of a mean. There are actions — I name adultery and murder in the Nicomachean Ethics — that are wrong in themselves, and for which no mean is possible; there is no right amount of them, no appropriate occasion, no virtuous mode of performance.10
The mean is a feature of domains where excess and deficiency are both genuine possibilities; it is not a universal license to find the moderate version of any act whatsoever.
With regard to feelings of fear and confidence courage is the mean; of the people who exceed, he who exceeds in fearlessness has no name (many of the states have no name), while the man who exceeds in confidence is rash, and he who exceeds in fear and falls short in confidence is a coward.Nicomachean Ethics
With regard to pleasures and pains- not all of them, and not so much with regard to the pains- the mean is temperance, the excess self-indulgence. Persons deficient with regard to the pleasures are not often found; hence such persons also have received no name. But let us call them 'insensible.'Nicomachean Ethics
the brave man appears rash relatively to the coward, and cowardly relatively to the rash man; and similarly the temperate man appears self-indulgent relatively to the insensible man, insensible relatively to the self-indulgent, and the liberal man prodigal relatively to the mean man, mean relatively to the prodigal.Nicomachean Ethics
The mean is more opposed to the extremes than the extremes are to each other, since the mean does not occur with either extreme, whereas the extremes often occur with one another. Sometimes the selfsame people are brazen cowards, or profligate in some respects and illiberal in others, or in general irregular in a bad way.Eudemian Ethics, p. 89
When people are irregular in a good way, they turn out to be cases of the mean, since in a way the extremes are at the mean.Eudemian Ethics, p. 89
Righteous indignation is a mean between envy and spite, and these states are concerned with the pain and pleasure that are felt at the fortunes of our neighbours; the man who is characterized by righteous indignation is pained at undeserved good fortune, the envious man, going beyond him, is pained at all good fortune, and the spiteful man falls so far short of being pained that he even rejoices.Nicomachean Ethics
Wit of such a kind - not as we use the term metaphorically - is the most decent state; and the mean point is praiseworthy, while the extremes are blameworthy.Eudemian Ethics, p. 89
Though all these mean points are praiseworthy, they are not virtues, nor are their opposites vices, since they do not involve decision. They all fall under the classification of affections, since each of them is a certain affection.Eudemian Ethics, p. 89
But because they are natural they contribute to the natural virtues. As will be discussed in what follows, each virtue in a way exists both naturally and, in conjunction with wisdom, otherwise.Eudemian Ethics, p. 89
But as there is no excess and deficiency of temperance and courage because what is intermediate is in a sense an extreme, so too of the actions we have mentioned there is no mean nor any excess and deficiency, but however they are done they are wrong; for in general there is neither a mean of excess and deficiency, nor excess and deficiency of a mean.Nicomachean Ethics