The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
38. For the True and so on are one and the same (vidyâ).
The text of the Vâgasaneyaka, after having enjoined the knowledge of the True, together with a meditation on the syllables of its name ('Whosoever knows this great glorious first-born as the true Brahman,' &c., Bri. Up. V, 4, 1), continues, 'Now what is the True, that is the Âditya, the person that dwells in yonder orb, and the person in the right eye' (V, 5, 2).--The doubt here arises whether the text enjoins two vidyâs of the True or one only.
Two, the pûrvapakshin maintains. For the text declares two different results, one in the earlier passage, 'He conquers these worlds' (V, 4, 1); the other one later on. 'He destroys evil and leaves it' (V, 5, 3). And what our opponent may call a reference to the subject-matter under discussion, 1 is merely due to the circumstance of the object of meditation being the same (in the two vidyâs).
To this we make the following reply.--There is only one vidyâ of the True, because the clause, 'That which is the True,' &c., refers back to that True which is treated
of in V, 4.--But has not the pûrvapakshin shown that the clause alluded to can be accounted for even on the supposition of there being two vidyâs?--The reasoning of the pûrvapakshin, we reply, would be admissible only if the separateness of the two vidyâs were established by some other clear and undoubted reason; in our ease, however, there is a general possibility of both (viz. of the vidyâs being separate or not), and the very circumstance that the mentioned clause contains a back reference to the True spoken of in V, 4, determines us to conclude that there is only one vidyâ of the True.--To the remark that there must be two vidyâs because the text states two different results, we reply that the statement of a second result merely has the purpose of glorifying the new instruction given about the True, viz. that its secret names are ahar and aham. Moreover, as in the case under discussion, the fruit of the vidyâ has really to be supplied from its arthavâda part 1, and as there is unity of vidyâ, all those fruits which the text states in connexion with the single parts of the vidyâ are to be combined and put in connexion with the vidyâ taken as a whole.--The conclusion therefore is that the text records only one vidyâ of the True, distinguished by such and such details, and that hence all the qualities mentioned, such as Truth and so on, are to be comprehended in one act of meditation.
Some commentators are of opinion that the above Sûtra refers (not to the question whether Bri. Up. V, 4 and V, 5 constitute one vidyâ but) to the question whether the Vâgasaneyaka-passage about the persons in the sun and in the eye, and the similar Khândogya-passage (I, 6, 6, 'Now that golden person who is seen within the sun,' &c.) form one vidyâ or not. They conclude that they do so, and that hence truth and the other qualities mentioned in
the Vâgasaneyaka are to be combined with the Khândogya-text also.--But this interpretation of the Sûtra appears objectionable. For the Khândogya-vidyâ refers to the udgîtha and is thus connected with sacrificial acts, marks of which connexion are exhibited in the beginning, the middle, and the end of the vidyâ. Thus we read at the beginning, 'The Rik is the earth, the Sâman is fire;' in the middle, 'Rik and Sâman are his joints and therefore he is udgîtha;' and in the end, 'He who knowing this sings a Sâman' (Kh. Up. I, 6, 1; 8; I, 7, 7). In the Vâgasaneyaka, on the other hand, there is nothing to connect the vidyâ with sacrificial acts. As therefore the subject-matter is different, the vidyâs are separate and the details of the two are to be held apart.
245:1 Viz. the clause in V, 5, 2, 'That which is the true,' which apparently--or really--connects the vidyâ of V, 5 with that of V, 4.
246:1 For the vidyâ contains no explicit statement that a man desirous of such and such a fruit is to meditate on the True in such and such a way.--That in cases where the fruit is not stated in a vidhi-passage it must be supplied from the arthavâda-passages, is taught in the Pû. Mî. Sû. IV, 3, eighth adhikarana.