168. Metaphysical considerations also are brought up against my explanation of the moral cause of moral evil; but they will trouble me less since I have dismissed the objections derived from moral reasons, which were more impressive.  These metaphysical considerations concern the nature of the possible and of the necessary; they go against my fundamental assumption that God has chosen the best of all possible worlds.  There are philosophers who have maintained that there is nothing possible except that which actually happens.  These are those same people who thought or could have thought that all is necessary unconditionally.  Some were of this [229] opinion because they admitted a brute and blind necessity in the cause of the existence of things:  and it is these I have most reason for opposing.  But there are others who are mistaken only because they misuse terms.  They confuse moral necessity with metaphysical necessity:  they imagine that since God cannot help acting for the best he is thus deprived of freedom, and things are endued with that necessity which philosophers and theologians endeavour to avoid.  With these writers my dispute is only one of words, provided they admit in very deed that God chooses and does the best.  But there are others who go further, they think that God could have done better.  This is an opinion which must be rejected:  for although it does not altogether deprive God of wisdom and goodness, as do the advocates of blind necessity, it sets bounds thereto, thus derogating from God’s supreme perfection.

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