These sections of the Discourse are the parts of the book that are closest in content to Descartes’ Meditations. Because of that they illustrate most clearly both Leibniz’s different style and the development of thinking about these issues in the decades since Descartes wrote.
• First note Leibniz’s modification in §23 of Descartes’ second proof of God’s existence.
• In contrast to Descartes’ rather casual use of the concepts of clearness and distinctness, Leibniz offers a very systematic and elaborate classification of ideas in §§24-25.
• In §§26-29, Leibniz is in part concerned with the source of ideas and the ways in which they can be said to be innate or derived from the senses. He will have more to say about the latter in the next work we will discuss, and the issue will be important when we turn to Locke.
But Leibniz is also concerned with an issue raised by Malebranche. Malebranche’s Cartesian philosophy emphasized dependence on God in ways that went beyond Descartes and influenced later thinkers. Thus Leibniz’s idea of pre-established harmony can be seen as a response to Malebranche’s doctrine of “occasionalism,” according to which God produces the effect of a causal interaction on the occasion of the cause occurring. Malebranche also held that the ideas that are the objects of our understanding are really in the mind of God, and thus that “we see all things in God” (to use the way Leibniz expresses this view in §23). Leibniz responds to this doctrine in §§28-29.