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)