ABSTRACT
This chapter aims to show how Honore Fabri distanced himself from the institutional framework by transforming his personal Aristotelianism into a claim for rational method. Fabri and the superiors of the Jesuits were playing a game about the source of truth. Both of them supposed that truth in philosophy and science was within human reach. Fabri's indebtedness to Descartes is evident. He is combining the famous cogito ergo sum with the traditional 'cosmological demonstration'. Evidence and certitude were common factors in Fabri's theory of nature, and he applied these criteria to reasoning itself so that in this case the existence of the foundation of being was inferred from the evidence of existence of the one who is reasoning. Fabri analysed Aristotelian concepts like vaguely known terms, supposing that they had become more and more complex during the history of commenting on them, including the scholastics of his century.
