BOOK III, PROP. XIII. When the mind conceives things which diminish or hinder the body’s power of activity, it endeavours, as far as possible, to remember things which exclude the existence of the first-named things.

Corollary.–Hence it follows, that the mind shrinks from conceiving those things, which diminish or constrain the power of itself and of the body.

Note.–From what has been said we may, clearly understand the nature of Love and Hate. Love is nothing else but pleasure accompanied by the idea, of an external cause: Hate is nothing else but pain accompanied by the idea of an external cause. We further see, that he who loves necessarily endeavours to have, and to keep present to him, the object of his love; while he who hates endeavours to remove and destroy the object of his hatred. But I will treat of these matters at more length hereafter.