Friendship is the source of the greatest pleasures, and without friends even the most agreeable pursuits become tedious.

I cannot go on.... All that I have written seems to me like so much straw compared to what I have seen and what has been revealed to me.

If... the motion of the earth were circular, it would be violent and contrary to nature, and could not be eternal, since ... nothing violent is eternal .... It follows, therefore, that the earth is not moved with a circular motion.

The soul is perfected by knowledge and virtue.

All the efforts of the human mind cannot exhaust the essence of a single fly.

Arrive at knowledge over small streamlets, and do not plunge immediately into the ocean, since progress must go from the easier to the more difficult.

Evil denotes the lack of good. Not every absence of good is an evil, for absence may be taken either in a purely negative or in aprivative sense. Mere negation does not display the character of evil, otherwise nonexistents would be evil and moreover, a thing would be evil for not possessing the goodness of something else, which would mean that man is bad for not having the strength of a lion or the speed of a wild goat. But what is evil is privation; in this sense blindness means the privation of sight.