In the human soul perception is developed into self-conscious thought, and there is, therefore, a vast difference between it and the mere monad (p. 464). As all knowledge is implicit in the soul, it follows that its perfection depends on the efficiency of the instrument by which it is developed. Hence the importance, in Leibnitz's system, of the logical principles and method, the consid eration of which occupied him at intervals throughout his whole career. There are two kinds of truths—(i) truths of reason, and (2) truths of fact (pp 83, 99, 707). The former rest on the principle of identity (or contradiction) or of possibility, in virtue of which that is false which contains a contradiction, and that true which is contradictory to the false. The latter rest on the princi ple of sufficient reason or of reality (compossibilite), according to which no fact is true unless there be a sufficient reason why it should be so and not otherwise (agreeing thus with the princip ium melioris or final cause). God alone, the purely active monad, has an a priori knowledge of the latter class of truths; they have their source in the human mind, only in so far as it mirrors the outer world, i.e., in its passivity, whereas the truths of reason have their source in our mind in itself or in its activity.
Both kinds of truths fall into two classes, primitive and deriva tive. The primitive truths of fact are, as Descartes held, those of internal experience, and the derivative truths are inferred from them in accordance with the principle of sufficient reason, by their agreement with our perception of the world as a whole. They are thus reached by probable reasoning—a department of logic which Leibnitz was the first to bring into prominence (pp. 84, 164, 168, 169, 343). The primitive truths of reasoning are identical (in later terminology, analytical) propositions, the de rivative truths being deduced from them by the principle of contradiction. The part of his logic on which Leibnitz laid the greatest stress was the analysis of these rational cognitions into their simplest elements—for he held that the root-notions (cogi tationes primae) would be found to be few in number (pp. 92, 93) —and the designation of them by universal characters or symbols,' composite notions being denoted by the formulae formed by the union of several definite characters, and judgments by the relation of aequipollence among these formulae, so as to reduce the syllo gism to a calculus. This is the main idea of Leibnitz's "universal characteristic," never fully worked out by him, which he regarded as one of the greatest discoveries of the age. An incidental result of its adoption would be the introduction of a universal symbolism of thought comparable to the symbolism of mathematics and in telligible to all thinkers (cf. p. 356). But the great revolution it would effect would chiefly consist in this, that truth and falsehood would be no longer matters of opinion but of correctness or error in calculation' (pp. 83, 84, 89, 93). The old Aristotelian analytic is not to be superseded ; but it is to be supplemented by this new method, for of itself it is but the ABC of logic.
As the perception of the monad when clarified becomes thought, so the appetite of which all monads partake is raised to will, their spontaneity to freedom, in man (p. 669). The will is an effort or tendency to that which one finds good (p. 251), and is free only in the sense of being exempt from external control (pp. 262, 513, 521), for it must always have a sufficient reason for its action de termined by what seems good to it. The end determining the will is pleasure (p. 269), and pleasure is the sense of an increase of perfection (p. 67o). A will guided by reason will sacrifice transi tory and pursue constant pleasures or happiness, and in this weighing of pleasures consists true wisdom. Leibnitz, like Spinoza, says that freedom consists in following reason, servitude in fol lowing the passions (p. 669), and that the passions proceed from 'Different symbolic systems were proposed by Leibnitz at different periods; cf. Kvet, Leibnitzens Logik (1857), p. 37.
places at which Leibnitz anticipated the modern theory of logic mainly due to Boole are pointed out in Mr. Venn's Symbolic Logic (1880 .
confused perceptions (pp. i88, 269). In love one finds joy in the happiness of another; and from love follow justice and law.
Theology.—Leibnitz makes the existence of God a postulate of morality as well as necessary for the realization of the monads. His theology is worked out in the Theodicee and his view of the universe as the best possible world defended. He contends that faith and reason are essentially harmonious (pp. 479), and that nothing can be received as an article of faith which contra dicts an eternal truth, though the ordinary physical order may be superseded by a higher. The ordinary arguments for the being of God are retained by Leibnitz in a modified form (p. 375). Des cartes's ontological proof is supplemented by the clause that God as the ens a se must either exist or be impossible (pp. 8o, 177, 708) ; in the cosmological proof he passes, from the infinite series of finite causes to their sufficient reason which contains all changes in the series necessarily in itself (pp. 147, 708) ; and he argues teleologically from the existence of harmony among the monads without any mutual influence to God as the author of this har mony (p. 430). In these proofs Leibnitz seems to have in view an extramundane power to whom the monads owe their reality, though such a conception evidently breaks the continuity and har mony of his system, and can only be externally connected with it. But he also speaks in one place at any rate' of God as the "uni versal harmony"; and the historians Erdmann and Zeller are of opinion that this is the only sense in which his system can be consistently theistic. Yet it would seem that to assume a purely active and therefore perfect monad as the source of all things is in accordance with the principle of continuity and with Leib nitz's conception of the gradation of existences. In this sense he sometimes speaks of God as the first or highest of the monads (p. 678), and of created substances proceeding from Him con tinually by "fulgurations" (p. 708) or by "a sort of emanation as we produce our thoughts."' With his thoroughgoing optimism Leibnitz has to reconcile the existence of evil in the best of all possible With this end in view he distinguishes (p. 655) between (1) metaphysical evil or imperfection, which is unconditionally willed by God as essen tial to created beings; (2) physical evil, such as pain, which is conditionally willed by God as punishment or as a means to greater good (cf. p. 51o) ; and (3) moral evil, in which the great difficulty lies, and which Leibnitz makes various attempts to ex plain. He says that it was merely permitted, not willed, by God (p. 655), and, that being obviously no explanation, adds that it was permitted because it was foreseen that the world with evil would nevertheless be better than any other possible world (p. 35o). He also speaks of the evil as a mere set-off to the good in the world, which it increases by contrast (p. 149), and at other times reduces moral to metaphysical evil by giving it a merely negative character, or says that their evil actions are to be re ferred to men alone, while it is only the power of action that comes from God, and the power of action is good (p. 658).
The great problem of Leibnitz's Theodicee thus remains un solved. The suggestion that evil consists in a mere imperfection, like his idea of the monads proceeding from God by a continual emanation, was too bold and too inconsistent with his immediate apologetic aim to be carried out by him. Had he done so his theory would have transcended the independence of the monads with which it started, and found a deeper unity in the world than that resulting from the somewhat arbitrary assertion that the monads reflect the universe.