The RIGHT OF NATURE, which Writers commonly call Jus Naturale, is the Liberty each man hath, to use his own power, as he will himself, for the preservation of his own Nature; that is to say, of his own Life; and consequently, of doing any thing, which in his own Judgement, and Reason, he shall conceive to be the aptest means thereunto.

The First Part, Chapter 14, p. 64. - Leviathan (1651)