"But here, perhaps, some man will ask whether those future things which are commonly called _contingents_, are necessary. I say, then, that generally all contingents have their necessary causes, but are called _contingents_, in respect of other events on which they do not depend--as the rain which shall be to-morrow shall be necessary, that is, from necessary causes; but we think and say, it happens by chance, because we do not yet perceive the causes thereof, though they exist now. For men commonly call that _casual_ or _contingent_, whereof they do not perceive the necessary cause: _and in the same manner they use to speak of things past, when not knowing whether a thing be done or not, they say, It is possible it never was done._ "Wherefore all propositions concerning future things, contingent or not contingent, as this--It will rain to-morrow, or To-morrow the sun will rise--are either necessarily true or necessarily false: but we call them contingent, because we do not yet know whether they be true or false; whereas their verity depends not upon our knowledge, but upon the foregoing of their causes. But there are some, who, though they will confess this whole proposition--_ To-morrow it will either rain or not rain_--to be true, yet they will not acknowledge the parts of it, as, _To-morrow it will rain_, or _To-morrow it will not rain_, to be either of them true by itself; because (they say) neither this nor that is true _determinately_. But what is this _true determinately_, but true _upon our knowledge_ or _evidently true_? And therefore they say no more but that it is not yet known whether it be true or not; but they say it more obscurely, and darken the evidence of the truth with the same words by which they endeavour to hide their own ignorance."] [Footnote 67: The reader will find this problem admirably handled in Mr. John Stuart Mill's System of Logic, Book iii. ch. 21, and Book vi. chs. 2 and 8; also in the volume of Professor Bain on the Emotions and the Will, Chapter on Belief.] Besides the above doctrine respecting Possible and Impossible, there is also ascribed to Diodorus a doctrine respecting Hypothetical Propositions, which, as far as I comprehend it, appears to have been a correct one.[68] He is also said to have reasoned against the reality of motion, renewing the arguments of Zeno the Eleate. [Footnote 68: Sextus Emp. Pyrrhon. Hypotyp. ii. pp. 110-115. [Greek: a)lêthe\s sunêmme/non]. Adv. Mathemat. viii. 112. Philo maintained that an hypothetical proposition was true, if both the antecedent and consequent were true--"If it be day, I am conversing". Diodorus denied that this proposition, as an Hypothetical proposition, was true: since the consequent might be false, though the antecedent were true. An Hypothetical proposition was true only when, assuming the antecedent to be true, the consequent must be true also.]