Aristotle

A friend is one soul abiding in two bodies.

Nature does not do anything in vain.

All men by nature desire to know. An indication of this is the delight we take in our senses; for even apart from their usefulness they are loved for themselves; and above all others the sense of sight. For not only with a view to action, but even when we are not going to do anything, we prefer sight to almost everything else. The reason is that this, most of all the senses, makes us know and brings to light many differences between things.

In every systematic inquiry where there are first principles, or causes, or elements, knowledge and science result from acquiring knowledge of these.

Happiness is thought to depend on leisure; for we are busy that we may have leisure, as we make war that we may live in peace.

Solvitur ambulando.

Knowing yourself is the beginning of all wisdom.

The things we have to learn before we can do them, we learn by doing them.

All men by nature desire to know.

Hope is the dream of a waking man.

We are what we repeatedly do. Excellence, then, is not an act, but a habit.

It is well said, then, that it is by doing just acts that the just man is produced, and by doing temperate acts the temperate man; without doing these no one would have even a prospect of becoming good. But most people do not do these, but take refuge in theory and think they are being philosophers and will become good in this way, behaving somewhat like patients who listen attentively to their doctors, but do none of the things they are ordered to do.

The young have exalted notions, because they have not been humbled by life or learned its necessary limitations; moreover, their hopeful disposition makes them think themselves equal to great things—and that means having exalted notions. They would always rather do noble deeds than useful ones: Their lives are regulated more by moral feeling than by reasoning.... All their mistakes are due to excess and vehemence and their neglect of the maxim of Chilon. They overdo everything; they love too much, hate too much, and the same with everything else. And they think they know everything, and confidently affirm it, and this is the cause of their excess in everything.

Misfortune shows those who are not really friends.

The liberal man will give to the right people, the right amounts, and at the right time, with all the other qualifications that accompany right giving; and that with pleasure or at least without pain.

For some identify happiness with virtue, some with practical wisdom, others with a kind of philosophic wisdom, others with these, or one of these, accompanied by pleasure or not without pleasure; while others include also external prosperity. Now ... it is not probable that these should be entirely mistaken, but rather that they should be right in at least some one respect or even in most respects.

Parents love their children as themselves; for their issue are by virtue of their separate existence a sort of other selves.

When people are friends, they have no need of justice, but when they are just, they need friendship in addition.