First published in 2002. This is Volume I of six in a series on Epistemology and Philosophy. This essay offers a critical study of the ideas of Emile Meyerson and is intended mainly to present a study of his complete work and to correct a fairly widespread misconception of it for its intrinsic interest. Meyerson's work offers an unusual paradigm in the light of which it is possible to think more clearly about the relevance of psychology to philosophical investigations.