Sutra 1.2.18

18. Not any other, on account of non-permanency of abode, and of impossibility.

As the reflected Self and the other Selfs mentioned by the Pūrvapakshin do not necessarily abide within the eye, and as conditionless immortality and the other qualities (ascribed in the text to the Person within the eye) cannot possibly belong to them, the Person within the eye cannot be any Self other than the highest Self. Of the reflected Self it cannot be said that it permanently abides within the eye, for its presence there depends on the nearness to the eye of another person. The embodied Self again has its seat within the heart, which is the root of all sense-organs, so as to assist thereby the activities of the different senses; it cannot therefore abide within the eye. And with regard to the divinity the text says that 'he rests with his rays in him, i.e. the eye': this implies that the divine being may preside over the organ of sight although itself abiding in another place; it does not therefore abide in the eye. Moreover, non-conditioned immortality and similar qualities cannot belong to any of these three Selfs. The Person seen within the eye therefore is the highest Self.

We have, under Sū. I, 2, 14, assumed as proved that the abiding within the eye and ruling the eye, which is referred to in Bṛ. Up. III, 7, 18 ('He who dwells in the eye,' etc.), can belong to the highest Self only, and have on that basis proved that the Self within the eye is the highest Self.—Here terminates the adhikaraṇa of that 'within.'—The next Sūtra now proceeds to prove that assumption.