_Answ._ It is one thing to express your present mind and resolution, without giving away the liberty of changing it; and it is another thing to intend the obliging of yourself to do the thing mentioned. And that obligation is either intended to man, or to God only; and that is either in point of rendition and use, or in point of veracity, or the performance of that moral duty of speaking truth. If you meant no more in saying, I will do it, or I will give it, but that this is your present will, and purpose, and resolution, yea, though it add the confident persuasion that your will shall not change; yet this no further obligeth you than you are obliged to continue in that will; and a man's confident resolutions may be lawfully changed upon sufficient cause. But if you intended to alienate the title to another, or to give him present right, or to oblige yourself for the future to him by that promise; or to oblige yourself to God to do it by way of peremptory assertion, as one that will be guilty of a lie if you perform it not; or if you dedicate the thing to God by those words as a vow; then you are obliged to do accordingly (supposing nothing else to prohibit it). _Quest._ XVII. Doth an inward promise of the mind not expressed, oblige? _Answ._ In a vow to God it doth; and if you intend it as an assertion obliging you in point of veracity, it doth so oblige you that you must lie. But it is no contract, nor giveth any man a title to what you tacitly thought of. _Quest._ XVIII. May I promise an unlawful thing (simply so) without an intention of performing it, to save my life from a thief or persecutor? Answ. No: because it is a lie, when the tongue agreeth not with the heart. Indeed those that think a lie is no sin when it hurteth not another, may justify this, if that would hold good; but I have before confuted it, part i. in the chapter against lying. _Quest._ XIX. May any thing otherwise unlawful become a duty upon a promise to do it?