_Rule_ XXIII. A former vow or promise is not nullified by a latter that contradicteth it.[74] Otherwise a man might disoblige himself at his pleasure. Yet he that maketh contrary vows, obligeth himself to contraries and impossibles; and bringeth a necessity of perjury on himself, for not doing the things impossible which he vowed. And in some cases a later promise to men may null a former, when we made the former with the reserve of such a power or liberty, or are justly supposed to have power, to recall a former promise: or when it is the duty of a mutable relation which we vow, (as of a physician, a schoolmaster, &c.) and by a later vow we change the relation itself (which we may still lawfully change).
_Rule_ XXIV. The _actus jurandi_ must still be distinguished from the _materia juramenti_; and it very often cometh to pass that the act of swearing (or the oath as our act) is unlawfully done, and was a sin from the beginning, and yet it is nevertheless obligatory as long as the _res jurata_, the matter sworn, is lawful or necessary.[75] Dr. Sanderson instanceth in Joshua's oath to the Gibeonites. The nature of the thing is proof enough; for many a thing is sinfully done, for want of a due call, or manner, or end, that yet is done, and is no nullity. A man may sinfully enter upon the ministry, that yet is bound to do the duty of a minister; and many marriages are sinful that are no nullities.
[Sidenote: What is the nullity of an oath.]
_Rule_ XXV. The nullity of an oath _ab initio_, is _quando realiter vel reputative non juravimus_; when really or reputatively we did not swear. The sinfulness of an oath is when we did swear really but unlawfully as to the ground, or end, or matter, or manner, or circumstances. Really that man did not swear, 1. Who spake not (mentally nor orally) the words of an oath. 2. Who thought those words had signified no such thing, and so had no intent to swear either mentally or verbally. As if an Englishman be taught to use the words of an oath in French, and made believe that they have a contrary sense. 3. Who only narratively recited the words of an oath, as a reporter or historian, without a real or professed intent of swearing. Reputatively he did not swear, 1. Who spake the words of an oath in his sleep, or in a deliration, distraction, madness, or such prevalent melancholy as mastereth reason; when a man is not _compos mentis_, his act is not _actus humanus_. (2.) When a man's hand is forcibly moved by another against his will to subscribe the words of an oath or covenant; for if it be totally involuntary it is not a moral act. But words cannot be forced; for he that sweareth to save his life, doth do it voluntarily to save his life. The will may be moved by fear, but not forced. Yet the person that wrongfully frighteneth another into consent, or to swear, hath no right to any benefit which he thought to get by force or fraud; and so _in foro civili_ such promises, or covenants, or oaths may _quoad effectum_ be reputatively null; and he that by putting his sword to another man's breast doth compel him to swear or subscribe and seal a deed of gift, may be judged to have no right to it, but to be punishable for the force; but though this covenant or promise be null _in foro humano_, because the person cannot acquire a right by violence, yet the oath is not a nullity before God; for when God is made a party, he hath a right which is inviolable; and when he is appealed to or made a witness, his name must not be taken in vain. 3. It is a nullity reputatively when the person is naturally incapable of self-obligation, as in infancy, when reason is not come to so much maturity as to be naturally capable of such a work; I say naturally incapable, for the reasons following.
_Rule_ XXVI. We must distinguish between a natural incapacity of vowing or swearing at all, and an incapacity of doing it lawfully; and between a true nullity, and when the oath is only _quasi nullum_, or as null _quoad effectum_, or such as I must not keep. There are many real oaths and vows which must not be kept, and so far are _quasi nulla_ as to the effecting of the thing vowed; but they are not simply null; for they have the effect of making the man a sinner and perjured. They are sinful vows, and therefore vows. A natural incapacity proveth it no vow at all; but if I am naturally capable, and only forbidden, (by God or man,) this maketh it not no vow, but a sinful vow, of which some must be kept and some must not.
[Sidenote: Cases in which a vow must not be kept.]
In these following cases a real vow is _quasi nullum_, or must not be kept.