of God (as it were, prior to their actualization), present, too, with all the distinctive properties and perfections that they now exhibit in a state of realization, so that their merely possible or conceivable being had the same content as their actual being, and their essence is not altered or increased by their existence.  Now, since the impulse toward actualization dwells in every possible essence, and is the more justifiable the more perfect the essence, a competition goes on before God, in which, first, those monod-possibilities unite which are mutually compatible or compossible, and, then, among the different conceivable combinations of monads or worlds that one is ordained for entrance into existence which shows the greatest possible sum of perfection.  It was, therefore, not the perfection of the single monad, but the perfection of the system of which it forms a necessary part, that was decisive as to its admission into existence.  The best world was known through God’s wisdom, chosen through his goodness, and realized through his power.[1] The choice was by no means arbitrary, but wholly determined by the law of fitness or of the best (principe du meilleur); God’s will must realize that which his understanding recognizes as most perfect.  It is at once evident that in the competition of the possible worlds the victory of the best was assured by the lex melioris, apart from the divine decision.

[Footnote 1:  In regard to the dependence of the world on God, there is a certain conflict noticeable in Leibnitz between the metaphysical interests involved in the substantiality of individual beings, together with the moral interests involved in guarding against fatalism, and the opposing interests of religion.  On the one side, creation is for him only an actualization of finished, unchangeable possibilities, on the other, he teaches with the mediaeval philosophers that this was not accomplished by a single act of realization, that the world has need of conservation, i.e., of continuous creation.]

This law is the special expression of a more general one, the principle of sufficient reason, which Leibnitz added, as of equal authority, to the Aristotelian laws of thought.  Things or events are real (and assertions true) when there is a sufficient reason for their existence, and for their determinate existence.  The principium rationis sufficientis governs our empirical knowledge of contingent truths or truths of fact, while, on the other hand, the pure rational knowledge of necessary or eternal (mathematical and metaphysical) truths rests on the principium contradictionis.  The principle of contradiction asserts, that is, whatever contains a contradiction is false or impossible; whatever contains no contradiction is possible; that whose opposite contains a contradiction is necessary.  Or positively formulated as the principle of identity, everything and every representative content is identical