For us, the Sein of something shows up only in discursive thinking and acting—that is, only when we take a thing as such-and-so, or in terms of this or that possibility. When I take something as, whether in theory or praxis, I understand the Sein of the thing, whether correctly or incorrectly. For Heidegger, “Understanding the Sein of a thing = understanding the what-it-is and how-it-is of that thing.”124 This whatness and howness is what Plato, Aristotle, and all metaphysics mean by the realness of the thing, its οὐσία, das Sein des Seienden. If we translate those ontological terms into a phenomenological framework, the argument comes out as follows:
1. To think or act dis-cursively entails “running back and forth” (discurrere) between the thing and its meaning, or the tool and the task, as we check out whether this thing actually does have that meaning or whether in fact this tool is suitable for that task.
2. Whenever we take something as this-or-that or as suitable for a task, we (rightly or wrongly) understand the current meaning that the thing has for us—ontologically, we understand das jeweilige Sein des Seienden, the current being of the thing.
3. But we can think and act discursively only by metaphorically “traversing the open space”125 between the tool and the task, or the thing and its possible meaning.
4. But that space (the clearing) must be already open and functioning in order for there to be an “as” or an “as-suitable-for” at all. That is, if we are to see the current meaning of some thing, there must be already operative a possible relation between the relata (between the thing and its meaning, or the tool and the task).
5. Hence, this already-operative possibility—the always-already thrown-open clearing—is what allows for all cases of meaningfulness (ontologically: all instances of the being of things).126
6. Therefore, the always-already-operative thrown-open clearing is the “thing itself” of all Heidegger’s work.127
124. GA 9: 131.21–22 = 103.33–35 : “Verständnis des Seins (Seinsverfassung: Was- und Wie-sein) des Seienden.”
125. GA 15: 380.6 = 68.43. See GA 14: 81.35 and 84.3–4 = 66.19 and 68.9 (durchmißt, duchmeßbaren) and GA 7: 19.12 = 18.32 (durchgeht).
126. Why “thrown-openness”? Answer: What Da-sein is thrown into is its own ex-sistence as the open clearing: SZ 276.16–17 = 321.11 with SZ 133.5 = 171.22.
127. Below we shall see that the thrown-open/appropriated-open clearing is the same as thrown-open/appropriated ex-sistence. See GA 73, 1: 585.19: “Er-eignet uns dem Da,” in italics; also 585.27: “in dem es [das Ereignis] uns dem Da er-eignet.”