CHAPTER iEi 493 1. Demonstrations a priori which prove the effect by its necessary cause; as, I prove the scripture is infallibly true, be- cause it is the word of God, who cannot lie. 2. Defnonstrations a posteriori, which infer the cause from its necessary effect : as, I infer there bath been the hand of some artificer here, because I find a curious figure. Or, I infer, there is a God, from the works of his wisdom in the visible world. The last of these is called denzonstratio s on, because it proves only the existence of a thing : the first is named demon - stratio Ts o-ion, because it shews also the cause of existence. But Note, That though these two sorts of arguments are most peculiarly called demonstrations, yet generally any strong and convincing- argument obtains that name ; and it is the custom of mathematicians to call all their arguments demonstrations, from what medium soever they derive them. III. Arguments are divided intoartificial and inartificiai. An artificial argument is taken from the nature and circum. stances of the things; and if the argument be strong, it produces a natural certainty ; as, The world was first created by God, be- cause nothing can create itself. An inartfciul argument is the testimony of another ; and this is called original, when our information proceeds immediate- ly from the persons concerned, or from eye or ear - witness of a fact : It is called tradition, when it is delivered by the report of others. We have taken notice before, the testimony is either divine or human. If the human testimony be strong, it produces a moral certainty; but divine testimony produces a supernatural certain- ty, which is far superior. Note, Arguments taken from human testimony, as well as from laws and rules of equity, are called moral ; and indeed the same name is also applied to every sort of argument which is drawn from the free actions of God, or the contingent actions of men, wherein we cannot arise to a natural certainty, but content ourselves with an high degree of probability, which in many cases is scarce inferior to natural certainty. IV. Arguments are either direct or indirect. It is a direct argument, where the middle term is such as proves the question itself; and infers that very proposition which was the matter of enquiry. An indirect or oblique argument, proves or refutes some other proposition, and thereby makes the thing enquired appear to be true by plain consequence. Several arguments are called indirect ; as, (1.) When some contradictory proposition is proved to be false, improbable or im- possible ; or when upon supposition of the falsehood, or denial of the original proposition, some absurdity is inferred. This is cal- led a proof per impossible, or a reductio ad absurdum. (2.) When
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