 Hartmann claims in Ontology: Laying the Foundations (1935) that the book “form[s] the prelude to an ontology that I have been working on for two decades,” and that “[a] new critical ontology has become possible. The task is to make it a reality” (v). The book paved the way for a systematic treatment of ontology by introducing (1) the difference between modes of being (the modalities of possibility, necessity and actuality), spheres of being (real and ideal), and ways of being (Dasein and Sosein), as well as (2) a treatment of emotional transcendent acts as constituting the requisite pre-conceptual acquaintance with the harshness of reality. The main thesis put forward by Hartmann in Laying the Foundations is that all ontological differences are categorial articulations of being, not differences between being and non-being. Parts and wholes are both authentic aspects of being; independent and dependent entities are similarly aspects of being; physical, biological, psychological and spiritual types of being are all manifestations of being, and none of them is “more being” than any other. From the point of view of ontology, no part, aspect, or moment of reality is “more being” than any other part, aspect or moment of it. The fact that, say, the existence of biological entities depends on that of physical entities does not imply that physics is “more ontologically real” than biology. Existentially dependent entities are as ontologically genuine as existentially independent ones. This basic premise is one of the points of departure for his ontological pluralism. All entities, whatever their type, demand the same careful ontological scrutiny. Hartmann’s analytic development of ontology begins with the theory of ontological modalities elaborated in Possibility and Actuality. The main purpose of this book is to demonstrate that modalities ground the differences between the two principal spheres of being (real and ideal) and the two secondary spheres of being (knowledge and logic). Finally, The Structure of the Real World and Philosophy of Nature present in detail the many fundamental and special categories within the real sphere of being.