_Rule_ II. Those conditions are to be taken as intended in all oaths, (whether expressed or no,) which the very nature of the thing doth necessarily imply[64] (unless any be so brutish as to express the contrary). And these are all reducible to two heads: 1. A natural, and, 2. A moral impossibility. 1. Whoever sweareth to do any thing, or give any thing, is supposed to mean, If I live; and if I be not disabled in my body, faculties, estate; if God make it not impossible to be, &c. For no man can be supposed to mean, I will do it whether God will or not, and whether I live or not, and whether I be able or not. 2. Whoever voweth or sweareth to do any thing, must be understood to mean it, If no change of providence make it a sin; or if I find not, contrary to my present supposition, that God forbiddeth it. For no man that is a christian is to be supposed to mean when he voweth, I will do this, though God forbid it, or though it prove to be a sin; especially when men therefore vow it, because they take it to be a duty. Now as that which is sinful is morally impossible, so there are divers ways by which a thing may appear or become sinful to us. (1.) When we find it forbidden directly in the word of God, which at first we understood not. (2.) When the change of things doth make that a sin, which before was a duty; of which may be given an hundred instances; as when the change of a man's estate, of his opportunities, of his liberty, of his parts and abilities, of objects, of customs, of the laws of civil governors, doth change the very matter of his duty.