1. "I demand of you, and of the whole world, that you show me a generic character... by which to distinguish between Man and Ape. I myself most assuredly know of none."
2. "Nature's economy shall be the base for our own, for it is immutable, but ours is secondary. An economist without knowledge of nature is therefore like a physicist without knowledge of mathematics."
3. "When all the thoughts are concerning one thing and the person loses interest in other things, the melancholy begins."