All art is concerned with coming into being; for it is concerned neither with things that are, or come into being by necessity, nor with things that do so in accordance with nature.
Now, the causes being four, it is the business of the student of nature to know about them all, and if he refers his problems back to all of them, he will assign the "why" in the way proper to his science-the matter, the form, the mover, that for the sake of which.
Since we think we understand when we know the explanation, and there are four types of explanation (one, what it is to be a thing; one, that if certain things hold it is necessary that this does; another, what initiated the change; and fourth, the aim), all these are proved through the middle term.
Not every action or emotion however admits of the observance of a due mean. Indeed the very names of some directly imply evil, for instance malice, shamelessness, envy, and, of actions, adultery, theft, murder. All these and similar actions and feelings are blamed as being bad in themselves; it is not the excess or deficiency of them that we blame. It is impossible therefore ever to go right in regard to them - one must always be wrong.
Every man should be responsible to others, nor should any one be allowed to do just as he pleases; for where absolute freedom is allowed, there is nothing to restrain the evil which is inherent in every man.
Bravery is a mean state concerned with things that inspire confidence and with things fearful ... and leading us to choose danger and to face it, either because to do so is noble, or because not to do so is base. But to court death as an escape from poverty, or from love, or from some grievous pain, is no proof of bravery, but rather of cowardice.
...the life which is best for men, both separately, as individuals, and in the mass, as states, is the life which has virtue sufficiently supported by material resources to facilitate participation in the actions that virtue calls for.
The physician himself, if sick, actually calls in another physician, knowing that he cannot reason correctly if required to judge his own condition while suffering.