While he is put into the Rationalist camp, Leibniz does not easily fit there. Leibniz published an entire work entitled New Essays on Human Understanding, addressing the empiricist conclusions of Locke, but decided not to publish the work when he learned of Locke’s death. In addition, he addressed the existence of evil and suffering and posited his concept of “the best of all possible worlds” as an explanation to the problem in his work of Theodicy.
Gottfried Wilhelm Leibniz was best known for contributions to mathematics, in particular with regard to the development of calculus. In fact he is credited with the discovery of calculus by some, while others credit Newton with the development of the mathematical calculus.
There are dimensions of Leibniz’s work that very closely resemble the conclusions of the empiricists. For example, he contended that much of our knowledge of contingent truths has its basis in sense perception (Cambridge Dictionary of Philosophy 2nd Edition, “Leibniz”, 494). His conclusions regarding necessary truths, however, reflect his belief that such truths have are a priori. (Cambridge Dictionary of Philosophy 2nd Edition, “Leibniz”, 494)
According to Leibniz, all truths are based on the Law of Non Contradiction and the Principle of Identity. The Law of Non Contradiction applies for necessary truths while the Principle of Sufficient Reason applies to contingent truths. Both of these items can be known apriori.
The Principle of Sufficient Reason in its classic form is simply that nothing is without a reason or there is no effect without a cause. As Leibniz remarks, this principle “must be considered one of the greatest and most fruitful of all human knowledge, for upon it is built a great part of metaphysics, physics, and moral science.” (G VII 301/L 227)
Leibniz also follows Aristotle in placing great emphasis on the Principle of Identity or the Principle of Non Contradiction. The principle states simply that “a proposition cannot be true and false at the same time, and that therefore A is A and cannot be not A” (G VI 355/AG 321).
