6. The monadology has very important consequences in reference to THE THEORY OF KNOWLEDGE. As the philosophy of Leibnitz, by its opposition to Spinozism, had to do with the doctrine of being, so by its opposition to the empiricism of Locke must it expound the theory of knowledge. Locke’s Essay on the Human Understanding had attracted Leibnitz without satisfying him, and he therefore attempted a new investigation in his _Nouveaux Essais_, in which he defended the doctrine of innate ideas. But this hypothesis of innate ideas Leibnitz now freed from that defective view which had justified the objections of Locke. The innateness of the ideas must not be held as though they were explicitly and consciously contained in the mind, but rather the mind possesses them potentially and only virtually, though with the capacity to produce them out of itself. All thoughts are properly innate, _i. e._ they do not come into the mind from without, but are rather produced by it from itself. Any external influence upon the mind is inconceivable, it even needs nothing external for its sensations. While Locke had compared the mind to an unwritten piece of paper, Leibnitz likened it to a block of marble, in which the veins prefigure the form of the statue. Hence the common antithesis between rational and empirical knowledge disappears with Leibnitz in the degrees of greater or less distinctness.—Among these theoretically innate ideas, Leibnitz recognizes two of special prominence, which take the first rank as principles of all knowledge and all ratiocination,—the principle of contradiction (_principium contradictionis_), and the principle of sufficient cause (_principium rationis sufficientis_). To these, as a principle of the second rank, must be added the _principium indiscernibilium_, or the principle that there are in nature no two things wholly alike.
7. The most elaborate exhibition of Leibnitz’s theological views is given in his _Théodicée_. The Théodicée, is, however, his weakest work, and has but a loose connection with the rest of his philosophy. Written at the instigation of a woman, it belies this origin neither in its form nor in its content—not in its form, for in its effort to be popular it becomes diffuse and unscientific, and not in its content, for it accommodates itself to the positive dogmas and the premises of theology farther than the scientific basis of the system of Leibnitz would permit. In this work, Leibnitz investigates the relation of God to the world in order to show a conformity in this relation to a final cause, and to free God from the charge of acting without or contrary to an aim. Why is the world as it is? God might have created it very differently. True, answers Leibnitz, God saw an infinite number of worlds as possible before him, but out of all these he chose the one which actually is as the best. This is the famous doctrine of the best world, according to which no more perfect world is possible than the one which is.—But how so? Is not the existence of evil at variance with this? Leibnitz answers this objection by distinguishing three kinds of evil, the metaphysical, the physical, and the moral. The metaphysical evil, _i. e._ the finiteness and incompleteness of things, is necessary because inseparable from finite existence, and is thus independent of the will of God. Physical evil (pain, &c.), though not independent of the will of God, is often a good conditionally, _i. e._ as a punishment or means of improvement. Moral evil or wickedness can in no way be charged to the will of God. Leibnitz took various ways to account for its existence, and obviate the contradiction lying between it and the conception of God. At one time he says that wickedness is only permitted by God as a _conditio sine qua non_, because without wickedness there were no freedom, and without freedom no virtue. Again, he reduces the moral evil to the metaphysical, and makes wickedness nothing but a want of perfection, a negation, a limitation, playing the same part as do the shadows in a painted picture, or the discords in a piece of music, which do not diminish the beauty, but only increase it through contrast. Again, he distinguishes between the material and the formal element in a wicked act. The material of sin, the power to act, is from God, but the formal element, the wickedness of the act, belongs wholly to man, and is the result of his limitation, or, as Leibnitz here and there expresses it, of his eternal self-predestination. In no case can the harmony of the universe be destroyed through such a cause.