Becoming means: coming to Being. Plato distinguishes three things: 1. τὸ γινομένον, that which becomes; 2. τὸ ἐν ᾧ γίγνεται, that within which it becomes, the medium in which something builds itself up while it is becoming and from which it then stands forth once it has become; 3. τὸ ὅθεν ἀφομοιούμενον, the source from which what becomes takes the standard of resemblance; for everything that becomes, everything that becomes something, takes what it becomes in advance as prototype.
To elucidate the meaning of παρεμφαίνω, we pay attention to what we mentioned under (2) above. That within which something becomes is what we call “space.” The Greeks have no word for “space.” This is no accident, for they do not experience the spatial according to extensio, but instead according to place (τόπος) as χώρα, which means neither place nor space, but what is taken up and occupied by what stands there. The place belongs to the thing itself. The various things each have their place. That which becomes is set into this place like “space” and is set forth from it.11 But in order for this to be possible, “space” must be bare of all the modes of appearance, any modes that it may receive from anywhere. For if it were like any one of the modes of appearance that enter into it, then in receiving forms, some opposed in essence to it, some of an entirely other essence, it would allow a bad actualization of the prototype to come to stand, since it would make manifest its own appearance in addition. ἄμορφον ὂν ἐκείνων ἁπασῶν τῶν ἰδεῶν ὅσας μέλλοι δέχεσθαι ποθεν. ὃμοιον γὰρ ὄν τῶν ἐπεισιόντων τινὶ τὰ τῆς ἐναντίας τά τε τῆς παράπαν ἄλλης φύσεως όπότ’ ἔλθοι δεχόμενον κακῶς ἂν ἀφομοιοῖ τὴν αᴜˊτοῦ παρεμφαῖνον ὄψιν.
11. In the next two sentences Heidegger paraphrases Timaeus 50d–e, which he then proceeds to quote. His main departure from conventional renderings is his translation of ἰδέα as “mode of appearance” as well as “form.”