701. Probabilism.--The meaning of Probabilism can be seen from a comparison with the opposite systems. (a) Unlike Probabiliorism and Equiprobabilism, Probabilism does not require a greater or equal probability, but permits one to follow what is less probable; (b) unlike Laxism, it does not allow one to follow what is only slightly or uncertainly probable, or to apply the system to all cases of doubt. 702. A judgment is probable when it is supported by arguments that make it seem true, although there may remain reasons for doubt. Examples are conclusions based on analogy, on hypothesis, on the opinions of others, or on the calculus of probabilities. 703. Probability is of various kinds. (a) It is absolute or relative, according as the supporting reasons are grave, either when considered alone, or when compared with the objections. Even the Probabiliorists admit that an opinion that is merely probable may be followed, if it is solidly probable and there is no argument against it (see 649). (b) We have solid or slight probability, according as the supporting motives are or are not such as would move, if not convince, a prudent man--that is, a man who shows good judgment in most things. (c) We have certain or uncertain probability, according as a person is sure or not, after reasonable consideration, that the arguments seem valid and the opinion likely. (d) Probability is internal or external, according as the arguments are drawn from the matter at issue itself (i.e., from its nature, properties, causes, effects, etc.) or from the authority of the doctors who have defended an opinion. 704. Relative probability according to logicians remains even when a lesser is compared with a greater probability. (a) If the opposing arguments are drawn from different sources, the more probable does not attack the less probable, and hence does not weaken its probability. Example: An intrinsic argument has more weight than a mere appeal to authority, but it does not attack the opposite argument, and hence does not diminish its probability. (b) If the opposing arguments are drawn from the same source, each one weakens the opposite, since there is direct opposition. But the more probable does not destroy the less probable, since, in spite of the greater appearance of truth on the one side, there still remains room for the possibility that the other side may be true. 705. A moral judgment is solidly probable when the following conditions are present: (a) For the judgment there must be an intrinsic or extrinsic argument that would be considered weighty by a prudent man. Example: An opinion that has the support of a universally acknowledged authority is strongly probable, whereas, if it has only the support of one obscure writer, it is only slightly probable.