Not only constructionism and naturalism are evidently contradictory, but they seem both perfectly extraneous to Leibniz's thbught. Nevertheless, it is possible to find important aspects of his thought that expose one or the other, and at times both attitudes. This paper will examine such aspects, focusing on various doctrines of Leibniz's that might give hints of such views (from general epistemology to philosophy of mathematics, from innatism to the theory of truth), to show that naturalistic and constructionist elements really play a role in Leibniz's view on the system of knowledge. This can also be shown to be connected rather with the richness and variety of his world view, than with an insufficient consistency of his doctrines.