Hi, for the background context on the passage (from Aristotle, Physics 209b13–16), I’m setting out here the analysis and commentary on this from Ross’ edition of the Physics (1936), in case helpful.
Analysis of Book IV, A (Place), 2 (Is Place matter or form?) (pgs 371–2), my underline:
209a31. A thing’s proper place is that in which it is directly present and which it fills; while the common place is that in which all bodies are because they are either directly in it or in something which is in it.
b1. If place proper is the direct container of a body, it will be a limit, so that the place of each thing would seem to be its form, by which its magnitude and matter are delimited.
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On the other hand, in so far as place seems to be the extension of the magnitude of a thing, i.e. what is contained and limited by the form, it seems to be matter or the unlimited; for when the boundary and the properties of a body are taken away, nothing is left but the latter.
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Hence Plato in the Timaeus identifies space and matter, making space identical with the ‘participative’ (though he gave a different account of the ‘participative’ in his unwritten lectures). While every one says place exists, he alone says what it is…
Commentary (pgs 565–6):
11–13. διὸ … ταὐτόν. It is correct to say that the Timaeus identifies χώρα and τὸ μεταληπτικόν. The latter phrase does not occur there, but τὴν τοῦ γεγονότος ὁρατοῦ καὶ πάντως αἰσθητοῦ μητέρα καὶ ὑποδοχὴν … ἀνόρατον εἶδός τι καὶ ἄμορφον, πανδεχές, μεταλαμβάνον δὲ ἀπορώτατά πῃ τοῦ νοητοῦ καὶ δυσαλωτότατον of 51a4–b1 is identified with χώρα in 52a8, b4 (where τόπος also is used, apparently without distinction of meaning, ἔν τινι τόπῳ καὶ κατέχον χώραν τινά), and d3. This, with παραδείγματα or Forms, is what Plato needs for the construction of the sensible world.
Aristotle’s phrase τὸ μεταληπτικόν may be due to a misrepresentation of the phrase μεταλαμβάνον δὲ … τοῦ νοητοῦ. That phrase does not mean ‘receptive of intelligible form’, but ‘sharing in intelligibility’ (as the context shows). But τὸ μεταληπτικόν is not a bad paraphrase of such words as ὑποδοκή and πανδεχές …
13–16. ἄλλον δὲ τρόπον … ἀπεφήνατο. Comparing this passage with b33–210a2 we see that the discrepancy between the Timaeus and the ‘unwritten doctrines’ was that in the latter the μεθεκτικόν or μεταληπτικόν was identified not with ὕλη (or rather, as we have seen in the previous note, not with χώρα) but with the great and small. The substitution of this for χώρα as the non-formal element may be explained by the fact that, while in the Timaeus Plato was discussing only the constitution of sensible things, he later carried his analysis further and performed an analysis of the Forms corresponding to that which he had already performed on sensible things. …