19. Likewise no man is tied by any compacts whatsoever to accuse himself, or any other, by whose damage he is like to procure himself a bitter life. Wherefore neither is a father obliged to bear witness against his son, nor a husband against his wife, nor a son against his father, nor any man against any one by whose means he hath his subsistence; for in vain is that testimony which is presumed to be corrupted from nature. But although no man be tied to accuse himself by any compact, yet in a public trial he may by torture be forced to make answer. But such answers are no testimony of the fact, but helps for the searching out of truth; so that whether the party tortured his answer be true or false, or whether he answer not at all, whatsoever he doth, he doth it by right. [Sidenote: The definition of an oath.] 20. Swearing is a speech joined to a promise, whereby the promiser declares his renouncing of God’s mercy, unless he perform his word. Which definition is contained in the words themselves, which have in them the very essence of an oath, to wit, _so God help me_, or other equivalent, as with the Romans, _do thou Jupiter so destroy the deceiver, as I slay this same beast_. Neither is this any let, but that an oath may as well sometimes be affirmatory as promissory; for he that confirms his affirmation with an oath, promiseth that he speaks truth. But though in some places it was the fashion for subjects to swear by their kings, that custom took its original hence, that those kings took upon them divine honour. For oaths were therefore introduced, that by religion and consideration of the divine power, men might have a greater dread of breaking their faiths, than that wherewith they fear men, from whose eyes their actions may lie hid. [Sidenote: The swearing must be conceived in that fashion which he uses who takes it.] 21. Whence it follows that an oath must be conceived in that form, which he useth who takes it; for in vain is any man brought to swear by a God whom he believes not, and therefore neither fears him. For though by the light of nature it may be known that there is a God, yet no man thinks he is to swear by him in any other fashion, or by any other name, than what is contained in the precepts of his own proper, that is (as he who swears imagines) the true religion. [Sidenote: Swearing adds nothing to the obligation which is by compact.]