Whenever a person strives, by the help of dialectic, to start in pursuit of every reality by a simple process of reason, independent of all sensuous information - never flinching, until by an act of the pure intelligence he has grasped the real nature of good - he arrives at the very end of the intellectual world.
Those who intend on becoming great should love neither themselves or their own things, but only what is just, whether it happens to be done by themselves or others.
It was Plato, according to Sosigenes, who set this as a problem for those concerned with these things, through what suppositions of uniform and ordered movements the appearances concerning the movements of the wandering heavenly bodies could be preserved.
A man who is good for anything ought not to calculate the chance of living or dying; he ought only to consider whether in doing anything he is doing right or wrong - acting the part of a good man or of a bad.
For neither birth, nor wealth, nor honors, can awaken in the minds of men the principles which should guide those who from their youth aspire to an honorable and excellent life, as Love awakens them
For it is obvious to everybody, I think, that this study [of astronomy] compels the soul to look upward and leads it away from things here to higher things.
That which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensation and without reason, is always in a process of becoming and perishing and never really is.