No science ever defends its first principles.

If the hammer and the shuttle could move themselves, slavery would be unnecessary.

It is not sufficient to know what one ought to say, but one must also know how to say it.

We have no evidence as yet about mind or the power to think; it seems to be a widely different kind of soul, differing as what is eternal from what is perishable; it alone is capable of existence in isolation from all other psychic powers.

It is clear that there is some difference between ends: some ends are energeia [energy], while others are products which are additional to the energeia.

Nature does nothing in vain. Therefore, it is imperative for persons to act in accordance with their nature and develop their latent talents, in order to be content and complete.

We do not know a truth without knowing its cause.