But in his later works the distinction of the ontological difference becomes hard and fast. Thus he notes that the philosophers after the great thinkers Parmenides and Heraclitus cease asking after being itself (Sein selbst); such philosophers as Plato and Aristotle, on the way to determining the being of things (Sein des Seienden), ground this being upon the "thingliness" of things (Seiendheit des Seienden). And this is what Heidegger means by the forgetting of being: it is the forgetting of the distinction between being and thing. The inquiry has turned from being to things, even though philosophers in this tradition of forgetfulness still speak of being. And it is with the forgetting if this distinction that the fate of being as the forgetting of being begins. This is, as Heidegger says, the significant and far-reaching event (Ereignis) that is metaphysics.

Nevertheless, not all the blame for being's subsequent misfortune should be put upon the shoulders of Plato and Aristotle; for as Heidegger says and as will become clearer in the following chapters, from the very start, even in the thought of the great pre-Socratic thinkers, being was destined to be forgotten. For there is a fundamental note of ambiguity to be found in the very notion of being as it is to be found among the pre-Socratics themselves. Being was characterized by the early Greek thinkers, says Heidegger, as the "presencing of the present" (Anwesen des Anwesenden). And the whole of the histry of western metaphysics might be said to be nothing but the destiny of this "twofold" (Zwiefalt). The fate of being hinged upon the ambiguity of the "twofold" because buried and unthought in this "twofold" was the failure to make the necessary ontological distinction between being and thing. Thus is Heidegger able to trace the destiny of being toward a forgetting of being back even to the thought of the great thinker Parmenides. As he says, the history of being begins and this, indeed, by necessity with a forgetting of being. Parmenides' celebrated maxim certainly names (nennt) being itself, but it thinks (denkt) the presencing (Anwesen) not as the presencing from out of its truth. And for Heidegger in the authentic truth "relationship" truth belongs to being. Being itself is being in its truth; and as such it can be thought only from out of its truth, a truth which as "unconcealness" (Unverborgenheit), as openness, is being's.

¶ 11:54 AM