Abstract

The purpose of this paper is to reconstruct the theoretical process through which Martin Heidegger in the 1910’s came to his idea of fundamental ontology. In particular, I will try to elucidate the necessity for him to introduce the concept of “existence” in ontological investigation. I will divide his development into three stages and make clear genetic relation between them. First, motivated by Catholic realism, Heidegger tried to explicate universal categorical structure of entity, which lead him to introduce concept of logical validity and normative account for cognition. Second, inspired by Lask’s account of objectity, Heidegger switched to ontology of signification and lived experience which gives condition of truth for the first stage. Third, motivated by religious experience of finitude, he came to the idea of existence which conditions facticity of signification and is thus regarded as the principal instance of ontology.