 Leibniz and his follower Christian Wolff were two of Kant’s most cited references. At one time or another, Kant addressed all of Leibniz’s main doctrines, including his defense of living forces against the Cartesians, his attack on absolute space and time against the Newtonians, his immaterial atomism or monadology, his theodicy, and his various principles and laws — the identity of indiscernibles, continuity, non-contradiction and sufficient reason. The challenging tone towards the followers of Leibniz that the young Kant, as an aspiring physicist and cosmologist, and later as a strong advocate of free will, adopted gave way in time to a more respectful engagement with the philosopher himself, as Kant became an increasingly determined critic of materialism.