Parmenides stated that “beings are” and consequently that non-beings are not. By identifying the ontological meaning of Being with the ontical totality of beings, he restricted and directed the understanding of Being for the Greeks. In Plato's Sophist, the Sophist and his discourse embodies non-beings, both his presence and discourse are an affront to the philosopher and his revealing logos, and thus paradoxically prove that non-beings are also. As such, one is forced to conclude against Parmenides that both beings and non-beings are. In order to explain this situation, Plato and Heidegger need to delve deep into the nature of beings, dialectic, logos, human soul, and fundamentally into the Being of beings and non-beings. For Heidegger, the project is much deeper – as he wants to show how Being appeared to the Greeks and in particular to Plato, to point their limitations, to demonstrate its continuity with what we take for granted today, and mainly to develop his new and radical ontological project.
For Plato and Aristotle, in logos we address something as presence in themselves (for example, a direct calling by name) or as something else in relation with (for example, an indirect addressing of something as something else). Thus, Being shows as pure presence or as the possibility of being-together with others. Naming something can never determine what is named in its substantive content; that is, naming or pointing are not properly disclosive logos. However, when addressing something as something, the underlying logos is substantial and disclosive. This co-presence with a pregiven world turns negation (i.e., no/non/not) from a trivial logical denial into a fundamental disclosive and exhibiting logos. Heidegger will later return and expand on negation, nothing, and the Being of non-beings - particularly in his professorship address “What is Metaphysics?”. The being-together and co-presence will be elaborated at length in “Being in Time” a few years later - as the phenomenon of Being-in in the antecedent uncoverdness of the world (i.e., being-in-the-world).
Since for Heidegger “Aristotle was not followed by anyone greater”, was more clear, more radical, more scientific, wrote systematic philosophy, and completed Plato's project – it hermetically makes sense for Heidegger to start and mostly to stay with Aristotle in this book and not directly with Plato.
The book is packed with ancient Greek words and sentences – far more than any other book I read. There is a glossary at the end, however the reading is still difficult and slow because of this.