tion of the premisses, as in the following : " If it is day. it is light ; but it is day, therefore Dion walks." a Of conclusive some are denoted by the common name of the whole class, " conclusive proper," others are called syllogistic. The syllogistic are such as either do not admit of, or are reducible to such as do not admit of, immediate proof in respect of one or more of the premisses ; e.g. " If Dion walks, then Dion is in motion ; but Dion is walking, therefore Dion is in motion." Conclusive specifically are those which draw conclusions, but not by syllogism ; e.g. the statement " It is both day and night " is false : " now it is day ; therefore it is not night." Arguments not syllogistic are those which plausibly resemble syllogistic arguments, but are not cogent proof; e.g. " If Dion is a horse, he is an animal ; but Dion is not a horse, therefore he is not an animal." Further, arguments may be divided into true and false. The former draw their conclusions by means of true premisses ; e.g. " If virtue does good, vice does harm ; but virtue does good, therefore vice does harm." b Those are false which have error in the premisses or are inconclusive ; e.g. " If it is day, it is light ; but it is day, therefore Dion is alive." Arguments may also be divided into possible and impossible, necessary and not necessary. Further, there are statements which are indemonstrable because they do not need demonstration ; they are employed in the construction of every argument. As to the number of these, authorities dhYer ; Chrysippus makes them five. These are assumed alike in reason- Cf. Sext. Emp. Adv. math. viii. 429. 6 The example is badly chosen, confusing contrary with contradictory.