So virtue is a purposive disposition, lying in a mean that is relative to us and determined by a rational principle, and by that which a prudent man would use to determine it. It is a mean between two kinds of vice, one of excess and the other of deficiency.

What is common to many is least taken care of, for all men have greater regard for what is their own than what they possess in common with others.

... the science we are after is not about mathematicals either none of them, you see, is separable.

...virtue is not merely a state in conformity with the right principle, but one that implies the right principle; and the right principle in moral conduct is prudence.

The ultimate end...is not knowledge, but action. To be half right on time may be more important than to obtain the whole truth too late.

Selfishness doesn't consist in a love to yourself, but in a big degree of such love.

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.