Reading : Western Philosophy VII.2 "Ethical Virtue"
Prior to this passage, Aristotle has discussed the concept of the "supreme good" and concluded that it must be:
Aristotle calls the supreme good "eudaimonia", which derives from "eu" (good) and "daimon" (daemon or spirit): perhaps "spiritually blessed" is a good way to render this. The translation in Cottingham uses the word "happiness"; others use "flourishing". It does not mean the same as "feeling happy", although it may include that. Since by definition, the "supreme good" cannot be improved upon, "it is nonsensical to go on asking why it should be pursued"1.
So this is where we stand at the start of the passage, which begins "To say that happiness is the supreme good seems something that is generally agreed". The problem Aristotle sets out to address is "what kind of life is like that?" Note that the question here is not what makes us happy, and not how we ought to live our lives, rather "he wants to instruct us in how to make a success of our lives"2.
Aristotle uses the word "function" to describe the characteristic behaviour of a particular thing that distinguishes it from other things. So the function of an axe might be to chop trees, and the function of a harpist might be to play the harp. If that is the case, then a "virtuous" thing is one which performs its function excellently: a good axe will be good at chopping trees; an good harpist will play the harp well. The word "virtue" (Greek areté) is used in the translation and roughly means "the best you can be".
To establish what would make an excellent human being, we need to understand the function, or characteristic behaviour, of human beings, and then fulfil that function excellently.
The function, or distinguishing feature, of human beings is to have "an activity of the soul and action expressing reason". Therefore, to achieve happiness, we must exercise "an activity of the soul in accordance with virtue" - we must perform the function of rationality to the best of our ability.
Aristotle says "Virtue is of two kinds, intellectual and ethical". Intellectual virtue is associated with intelligence and wisdom, and increases through learning, or being taught. He concentrates more on ethical virtue, by which he means morality.
In the case of ethical virtue, this is an ability which, like playing the harp, is acquired through habit and practice. In the same way that a child practises playing the harp until it becomes second nature, we develop moral instincts by habitually behaving in an ethically virtuous fashion: "activities of a certain kind produce corresponding dispositions".
"Virtue ... is a disposition concerned with choice, lying on a mean ... between two vices". Aristotle puts forward the idea of a mean which lies between two excesses of vice. So for example, between the to extremes of prodigality and stinginess lies the mean of being generous. This is not to say that the mean is right in the middle of the two extremes, rather that it is the carefully judged point between them. The point may vary depending on circumstances: the way in which it is judged should be a matter of habit for the ethically virtuous person. When confronted with a moral choice, we might ask "what would a virtuous person do in this situation?"
This means that we do not become virtuous by learning rules, rather by acquiring, through habit, dispositions which result in us choosing the "mean" option appropriate to any given circumstance. This suggests that the question "is not: what ought I to do? but rather: what dispositions should I acquire?"2.