Nicomachean Ethics VII.10

Finally, the last chapter on incontinence.

Nor can the same man have practical wisdom and be incontinent; for it has been shown that a man is at the same time practically wise, and good in respect of character. Further, a man has practical wisdom not by knowing only but by being able to act; but the incontinent man is unable to act-there is, however, nothing to prevent a clever man from being incontinent; this is why it is sometimes actually thought that some people have practical wisdom but are incontinent, viz. because cleverness and practical wisdom differ in the way we have described in our first discussions, and are near together in respect of their reasoning, but differ in respect of their purpose-nor yet is the incontinent man like the man who knows and is contemplating a truth, but like the man who is asleep or drunk.

Indeed, the incontinent man is likely to be drunk; excessive drinking is the clearest case of incontinence, though not the only one.  

There's a slight ambiguity there that I think is helpfully cleaned up: the incontinent man isn't unable to act per se, but unable to act in accord with what he knows is the right rule. He does act, just not well. 

And [the incontinent man] acts willingly (for he acts in a sense with knowledge both of what he does and of the end to which he does it), but is not wicked, since his purpose is good; so that he is half-wicked. And he is not a criminal; for he does not act of malice aforethought; of the two types of incontinent man the one does not abide by the conclusions of his deliberation, while the excitable man does not deliberate at all. And thus the incontinent man like a city which passes all the right decrees and has good laws, but makes no use of them, as in Anaxandrides' jesting remark,

The city willed it, that cares nought for laws; but the wicked man is like a city that uses its laws, but has wicked laws to use.

Now incontinence and continence are concerned with that which is in excess of the state characteristic of most men; for the continent man abides by his resolutions more and the incontinent man less than most men can.

Strictly applied, that makes "most men" neither continent nor incontinent in what Aristotle likes to call 'the unrestricted sense' of the terms; most men therefore vary between the states, rather than being defined by either state. 

Of the forms of incontinence, that of excitable people is more curable than that of those who deliberate but do not abide by their decisions, and those who are incontinent through habituation are more curable than those in whom incontinence is innate; for it is easier to change a habit than to change one's nature; even habit is hard to change just because it is like nature, as Evenus* says:

I say that habit's but a long practice, friend,

And this becomes men's nature in the end.

So this is a version of what will end up being a core doctrine for Aristotle, the idea of 'second nature.' I have spoken of this already, in the commentary on VI.13; the idea is going to be that you have a 'first nature,' i.e. the nature you are born with, and also a 'second nature,' that which your habituation builds into a permanent character. The second nature will end up being dominant over the first nature, training and guiding it, yet will be as difficult to defy as your first nature can be. 

We have now stated what continence, incontinence, endurance, and softness are, and how these states are related to each other.

This is one of the longer inquiries in the EN, and not the most pleasant. The inquiry into friendship will be of more interest to most of you, I think. 

* I'm not sure which Evenus is intended by Aristotle here; probably not the river god, but perhaps one of the other two associated with the Iliad. However, my guess is it really might be Evenus the poet, whom Socrates mentions in the Phaedo and to whom Socrates ascribes the character of a philosopher.