The purpose of this book is to address the controversial issues of whether we have a fixed set of ontological categories and if they have some epistemic value at all. Which are our ontological categories? What determines them? Do they play a role in cognition? If so, which? What do they force to presuppose regarding our world-view? If they constitute a limit to possible knowledge, up to what point is science possible? Does their study make of philosophy a science?Departing from the novelty -but no exclusively- of considering distinctions to be the subject matter of thought and language -that is, of reference and meaning- the author arrives to a radical novel conception of the ontological categories. The observations and arguments presented in it constitute a strong case against established and well-rooted tenets, if not paradigms, of contemporary philosophy beyond ontology and epistemology. The conclusions arrived at open the door to a revival of the discipline, and the importance of its studies as the science of the constitutive elements of knowledge of a non-empirical nature.