by attempting to bring them into their Being, that is, sets beings into limits and form, projects something new (not yet present), originally poetizes, grounds poetically.
The thinking of Parmenides and Heraclitus is still poetic, and here this means philosophical, not scientific. But because in this poetizing thinking, thinking has precedence, thinking about human Being also acquires its own direction and measure. In order to clarify this poetic thinking sufficiently in terms of its proper counterpart, we will now interrogate a thinking poetry of the Greeks. This poetry is tragedy—the poetry in which Greek Being and Dasein [a Dasein belonging to Being]50 were authentically founded.
We want to understand the separation between “Being and thinking” [111|153] in its origin. This is the title for the fundamental attitude of the Western spirit. In accordance with it, Being is determined from the perspective of thinking and reason. This is the case even where the Western spirit withdraws from the mere dominance of reason by wanting the “irrational” and seeking the “alogical.”
As we pursue the origin of the separation between Being and thinking, we encounter the saying of Parmenides: τὸ γὰρ αὐτὸ νοεῖν ἔστιν τε καὶ εἶναι. According to the customary translation and reading, it says: thinking and Being are the same.
We can call this saying the guiding principle of Western philosophy, but only if we attach the following note to it:
The saying became the guiding principle of Western philosophy only after it was no longer understood, because its originary truth could not be held fast. The Greeks themselves began to fall away from truth of the saying right after Parmenides.
50. In parentheses in the 1953 edition.