The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space.

From such crooked wood as that which man is made of, nothing straight can be fashioned.

Apart from moral conduct, all that man thinks himself able to do in order to become acceptable to God is mere superstition and religious folly.

Give me matter, and I will construct a world out of it!

He who has made great moral progress ceases to pray

Most men use their knowledge only under guidance from others because they lack the courage to think independently using their own reasoning abilities. It takes intellectual daring to discover the truth.

If man makes himself a worm he must not complain when he is trodden on.