But if God was free to decree the creation of the world, He was not free in the choice between different possible worlds. Thus Leibniz, while wishing to avoid the voluntarism of Descartes and the absolute necessity of Spinoza , winds up by approaching this latter, and finishes by conceiving of the world as forming and shaping itself under the necessity of the principle of sufficient reason. In a world which, according to the concept of Leibniz, is the best possible world, the question of the existence of evil must be answered. Leibniz treats of this question in his Theodicy . This privation, which is not due to the nature of being, is not a real evil.
Physical evil consists in a privation of a perfection due to the nature of the being.
This is a real evil, but Leibniz justifies its existence on the basis of aesthetic motives, and also holds that it results in benefit to nature taken in its entirety. Man, not God, is responsible for moral evil. The man-monad is not only apperceptive, but also appetitive, and hence free. Man abuses this freedom and opposes himself to the will of God. Moral evil consists in this opposition and man alone is responsible for it.