169. The question of the _possibility of things that do not happen_ has already been examined by the ancients. It appears that Epicurus, to preserve freedom and to avoid an absolute necessity, maintained, after Aristotle, that contingent futurities were not susceptible of determinate truth. For if it was true yesterday that I should write to-day, it could therefore not fail to happen, it was already necessary; and, for the same reason, it was from all eternity. Thus all that which happens is necessary, and it is impossible for anything different to come to pass. But since that is not so it would follow, according to him, that contingent futurities have no determinate truth. To uphold this opinion, Epicurus went so far as to deny the first and the greatest principle of the truths of reason, he denied that every assertion was either true or false. Here is the way they confounded him: 'You deny that it was true yesterday that I should write to-day; it was therefore false.' The good man, not being able to admit this conclusion, was obliged to say that it was neither true nor false. After that, he needs no refutation, and Chrysippus might have spared himself the trouble he took to prove the great principle of contradictories, following the account by Cicero in his book _De Fato_: 'Contendit omnes nervos Chrysippus ut persuadeat omne [Greek: Axioma] aut verum esse aut falsum. Ut enim Epicurus veretur ne si hoc concesserit, concedendum sit, fato fieri quaecunque fiant; si enim alterum ex aeternitate verum sit, esse id etiam certum; si certum, etiam necessarium; ita et necessitatem et fatum confirmari putat; sic Chrysippus metuit ne non, si non obtinuerit omne[230] quod enuncietur aut verum esse aut falsum, omnia fato fieri possint ex causis aeternis rerum futurarum.' M. Bayle observes (_Dictionary_, article 'Epicurus', let. T, p. 1141) 'that neither of these two great philosophers [Epicurus and Chrysippus] understood that the truth of this maxim, every proposition is true or false, is independent of what is called _fatum_: it could not therefore serve as proof of the existence of the _fatum_, as Chrysippus maintained and as Epicurus feared. Chrysippus could not have conceded, without damaging his own position, that there are propositions which are neither true nor false. But he gained nothing by asserting the contrary: for, whether there be free causes or not, it is equally true that this proposition, The Grand Mogul will go hunting to-morrow, is true or false. Men rightly regarded as ridiculous this speech of Tiresias: All that I shall say will happen or not, for great Apollo confers on me the faculty of prophesying. If, assuming the impossible, there were no God, it would yet be certain that everything the greatest fool in the world should predict would happen or would not happen. That is what neither Chrysippus nor Epicurus has taken into consideration.' Cicero, lib. I, _De Nat.