ἀεὶ ἀπορούμενον, τί τὸ ὄν, τοῦτό ἐστι τίς ἡ οὐσία.2 "That which has been sought for from of old and now and in the future and constantly, and that on which inquiry founders over and over again, is the problem What is being?" If philosophy is the science of being, then the first and last and basic problem of philosophy must be, What does being signify? Whence can something like being in general be understood? How is understanding of being at all possible?
Before we broach these fundamental questions, it will be worthwhile first to make ourselves familiar for once with discussions about being. To this end we shall deal in the first part of the course with some characteristic theses about being as individual concrete phenomenological problems, theses that have been advocated in the course of the history of Western philosophy since antiquity. In this connection we are interested, not in the historical contexts of the philosophical inquiries within which these theses about being make their appearance, but in their specifically inherent content. This content is to be discussed critically, so that we may make the transition from it to the above-mentioned basic problems of the science of being. The discussion of these theses should at the same time render us familiar with the phenomenological way of dealing with problems relating to being. We choose four such theses:
1. Kant's thesis: Being is not a real predicate.
2. The thesis of medieval ontology (Scholasticism) which goes back to Aristotle: To the constitution of the being of a being there belong (a) whatness, essence (Was-sein, essentia), and (b) existence or extantness (existentia, Vorhandensein).
3. The thesis of modern ontology: The basic ways of being are the being of nature (res extensa) and the being of mind (res cogitans).
4. The thesis of logic in the broadest sense: Every being, regardless of its particular way of being, can be addressed and talked about by means of the "is." The being of the copula.
These theses seem at first to have been gathered together arbitrarily. Looked at more closely, however, they are interconnected in a most intimate way. Attention to what is denoted in these theses leads to the insight
2. Aristotle, Metaphysica, book Zeta, 1. 1028b2 ff.