A Law of Nature, (Lex Naturalis) is a Precept, or general Rule, found out by Reason, by which a man is forbidden to do, that, which is destructive of his life, or taketh away the means of preserving the same; and to omit, that, by which he thinketh it may be best preserved.

The Moral and Political Works of Thomas Hobbes of Malmesbury (ed. 1750)