In this withdrawal (or intrinsic hiddenness), the clearing’s utmost closeness consists in the Da, the open, insofar as it ap-propri-ates [brings into its proper condition] our being-the-open.154

Heidegger says the clearing is what is “hidden in the first and primary sense.”155 He is arguing that the clearing is intrinsically unknowable, if “knowing” means discerning the reason for something, what Aristotle would call “knowing the αἰτία of something.”156 The open space that makes possible the distinguishing-and-synthesizing whereby we understand things as meaningfully present is not available to the discursive intellect. It can be experienced in the non-discursive immediacy of dread or wonder (Heidegger’s rewriting of the function of Aristotelian νοῦς).157 However, such an encounter with the clearing robs us of speech158 because

[t]he clearing is itself “the immediate.” Therefore nothing mediate [such as discursive speech] . . . can ever attain the immediate immediately.159

Heidegger’s point: Insofar as our appropriation is what lets us make sense of things at all, it is the προϋποκείμενον πρῶτον, the praesuppositum primum, of everything human and thus of all knowing and doing.160 As the ultimate presupposition, the clearing must always be presupposed in any attempt to know it. It always lies “behind” us, so to speak, and it will always remain behind us (i.e., unknowable) even when we turn around to take a look at it. Consequently, we cannot go “beyond” or “behind” it without contradicting ourselves. We cannot (without moving in a vicious circle) seek the presupposition of this ultimate presupposition of all our seeking. “There is nothing else to which appropriation could be led back or in terms of which it could be explained.”161

154. GA 65: 249.15–18 = 196.21–24: “Aber in diesem Sichentziehen (Sichverbergen) hat das Seyn seine nächste Nähe in der Lichtung des Da, indem es das Da-sein er-eignet.”
155. GA 9: 194.11–12 = 148.26–27: “das erstlich Verborgene.”
156. Posterior Analytics I 2, 71b10–11: τὴν αἰτίαν γιγνώσκειν. See “rerum cognoscere causas”: Virgil, Georgics II, 490, repeated in the tondo of Rafael’s “School of Athens” in the papal apartments in the Vatican, La Stanza della Segnatura.
157. See Metaphysics IX 10, 1051b24. Heidegger retrieves the unmediated θιγεῖν performed by νοῦς as the θαυμάζειν that is dread or wonder. Cf. GA 11: 22.11 and .14 = 85.1 and 85.4–5: “θαυμάζειν, das Erstaunen” and “Zurücktreten vor dem Sein”—that is, vor der Lichtung.
158. GA 9: 112.14 = 89.5: “Der Angst verschlächt uns das Wort.”
159. GA 4: 61.21–23 = 83.27–29: “Das Offene selbst ist das Unmittelbare. Kein Mittelbares . . . vermag deshalb je das Unmittelbare unmittelbar zu erreichen.”
160. On προϋποκείμενον as that which is always already (πρό) under (ὑπό) lying (κείμενον) see Damascius, De Principiis III, 153.2 = Dubitationes et solutions I, 312.21.
161. GA 12: 247.12–13 = 127.28–30. GA 10: 169.6 = 113.18 (referring to Heraclitus, fragment 52): “Das ‘Weil’ versinkt im Spiel. Das Spiel ist ohne ‘Warum.’”

Thomas Sheehan - Making Sense of Heidegger