In this discussion the term "phenomenology" will be used to refer to Husserl's constitutive phenomenology and not to later philosophical trends, which, whatever their kinship with Husserl's phenomenology, have developed in somewhat different directions. First, a brief sketch of the fundamental principles of phenomenology with special regard to the problem of existence will be presented. Next, the terns will be set forth in which ontological problems can be treated in phenomenology. Last, two ontological theses will be submitted.