Note 84 — Chapter XXIII · THE NEW ACADEMY.

Belief, however, like probability, is of several degrees. The lowest degree of probability arises when a notion produces by itself an impression of truth, without being taken in connection with other notions. The next higher degree is when that impression is confirmed by the agreement of all notions which are related to it. The third and highest degree is when an investigation of all these notions results in producing the same corroboration for all. In the first case a notion is called probable (πιθανή); in the second probable and undisputed (πιθανὴ καὶ ἀπερίσπαστος); in the third probable, undisputed, and tested (πιθανὴ καὶ ἀπερίσπαστος καὶ περιωδευμένη).84 Within each one of these three classes different gradations of probability are again possible.85 The distinguishing marks, which must be considered in the investigation of probability, appear to have been investigated by Carneades in the spirit of the Aristotelian logic.86 In proportion to the greater or less practical importance of a question, or to the accuracy of investigation which the circumstances allow, we must adhere to one or the other degree of probability.87 Although no one of them is of such a nature as to exclude the possibility of error, this circumstance need not deprive us of certainty in respect to actions, provided we have once convinced ourselves that the absolute certainty of our practical premisses is not possible.88 Just as little should we hesitate to affirm or deny anything in that conditional way which is alone possible after what has been stated. Assent will be given to no notion in the sense of its being absolutely true, but to many notions in the sense that we consider them highly probable.89