I am not an Athenian or a Greek, but a citizen of the world.

It is not living that matters, but living rightly.

I know that I know nothing.

The unexamined life is not worth living.

No one desires evil.

Reserve your right to think, for even to think wrongly is better than not to think at all.

-- Hypatia

Behold what is absent as firmly present through the mind.

-- Parmenides

Intelligence is the ability to adapt to change.

-- Stephen Hawking

The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.

-- Bertrand Russell

Knowledge is the conformity of the object and the intellect.

-- Averroes

I know that I do not know.

-- Plato