The highest form of pure thought is in mathematics.

There will be no end to the troubles of states,Or of humanity itself,Till philosophers become kings in this world,Or till those we now call kings and rulers really And truly become philosophers

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.

But that we shall be better and braver and less helpless if we think that we ought to enquire, than we should have been if we indulged in the idle fancy that there was no knowing and no use in seeking to know what we do not know; - that is a theme upon which I am ready to fight, in word and deed, to the utmost of my power.

... what we can be positive about is what we have just said, namely that they must be given the right education, whatever that may be, as the surest way to make them behave humanely to each other and the subjects in their charge.

Man is a prisoner who has no right to open the door of his prison and run away... A man should wait, and not take his own life until God summons him.

Man is a two-legged animal without feathers.