The one exclusive sign of thorough knowledge is the power of teaching.

For what is the best choice for each individual is the highest it is possible for him to achieve.

No one chooses what does not rest with himself, but only what he thinks can be attained by his own act.

Happiness is a thing honored and perfect. This seems to be borne out by the fact that it is a first principle or starting-point, since all other things that all men do are done for its sake; and that which is the first principle and cause of things good we agree to be something honorable and divine.

Tools may be animate as well as inanimate; for instance, a ship's captain uses a lifeless rudder, but a living man for watch; for a servant is, from the point of view of his craft, categorized as one of its tools. So any piece of property can be regarded as a tool enabling a man to live, and his property is an assemblage of such tools; a slave is a sort of living piece of property; and like any other servant is a tool in charge of other tools.

Sophocles said he drew men as they ought to be, and Euripides as they were.

That which is impossible and probable is better than that which is possible and improbable.