Leibniz's rationality of the theory of knowledge is characterized by two fundamental features: the first is the conformity between the theoretical methodological fundamentals of knowledge and the metaphysical roots of human knowledge. The second is his attempt to conform between philosophical patterns opposite in their stance to the knowledge. So, to what extent the monad philosopher contributed to setting up logical pillars for the knowledge?. How successful was he in linking the epistemology to ontology?. And how influential was he in establishing a critical stance compatible with the knowledge?, These questions are the core of the present research.