The most useful piece of learning for the uses of life is to unlearn what is untrue.
The advantages of philosophy? That I am able to hold converse with myself.
The investigation of the meaning of words is the beginning of education.
The most necessary learning is that which unlearns evil.
We weed out the darnel from the corn and the unfit in war, but do not excuse evil men from the service of the state.
We must not contradict, but instruct him that contradicts us; for a madman is not cured by another running mad also.