The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
31. If it be said (that Brahman is) not (meant), on account of characteristic marks of the individual soul and the chief vital air (being mentioned); we say no, on account of the threefoldness of devout meditation (which would result from your interpretation); on account of (the meaning advocated by us) being accepted (elsewhere); and on account of (characteristic marks of Brahman) being connected (with the passage under discussion).
Although we admit, the pûrvapakshin resumes, that the chapter about the prâna does not furnish any instruction regarding some outward deity, since it contains a multitude of references to the interior Self; still we deny that it is concerned with Brahman.--For what reason?--Because it mentions characteristic marks of the individual soul on the one hand, and of the chief vital air on the other hand. The passage, 'Let no man try to find out what speech is, let him know the speaker,' mentions a characteristic mark of the individual soul, and must therefore be held to point out as the object of knowledge the individual soul which rules and employs the different organs of action such as speech and so on. On the other hand, we have the passage, 'But prâna alone, the intelligent Self, having laid hold of this body makes it rise up,' which points to the chief vital air; for the chief attribute of the vital air is that it sustains the body. Similarly, we read in the colloquy of the vital airs (Pra. Up. II, 3), concerning speech and the other vital airs, 'Then prâna (the chief vital air) as the best said to them: Be not deceived; I alone dividing myself fivefold support this body and keep it.' Those, again, who in the
passage quoted above read 'this one (masc.), the body 1' must give the following explanation, Prâna having laid hold of this one, viz. either the individual soul or the aggregate of the sense organs, makes the body rise up. The individual soul as well as the chief vital air may justly be designated as the intelligent Self; for the former is of the nature of intelligence, and the latter (although non-intelligent in itself) is the abode of other prânas, viz. the sense organs, which are the instruments of intelligence. Moreover, if the word prâna be taken to denote the individual soul as well as the chief vital air, the prâna and the intelligent Self may be spoken of in two ways, either as being non-different on account of their mutual concomitance, or as being different on account of their (essentially different) individual character; and in these two different ways they are actually spoken of in the two following passages, 'What is prâna that is pragñâ, what is pragñâ that is prâna;' and, 'For together do these two live in the body and together do they depart.' If, on the other hand, prâna denoted Brahman, what then could be different from what? For these reasons prâna does not denote Brahman, but either the individual soul or the chief vital air or both.
All this argumentation, we reply, is wrong, 'on account of the threefoldness of devout meditation.' Your interpretation would involve the assumption of devout meditation of three different kinds, viz. on the individual soul, on the chief vital air, and on Brahman. But it is inappropriate to assume that a single sentence should enjoin three kinds of devout meditation; and that all the passages about the prâna really constitute one single sentence (one syntactical whole) appears from the beginning and the concluding part. In the beginning we have the clause 'Know me only,' followed by 'I am prâna, the intelligent Self, meditate on me as Life, as Immortality;' and in the end we read, 'And that prâna indeed is the intelligent Self, blessed, imperishable, immortal.' The beginning and the concluding part are thus seen to be similar, and we
therefore must conclude that they refer to one and the same matter. Nor can the characteristic mark of Brahman be so turned as to be applied to something else; for the ten objects and the ten subjects (subjective powers) 1cannot rest on anything but Brahman. Moreover, prâna must denote Brahman 'on account of (that meaning) being accepted,' i.e. because in the case of other passages where characteristic marks of Brahman are mentioned the word prâna is taken in the sense of 'Brahman.' And another reason for assuming the passage to refer to Brahman is that here also, i.e. in the passage itself there is 'connexion' with characteristic marks of Brahman, as, for instance, the reference to what is most beneficial for man. The assertion that the passage, 'Having laid hold of this body it makes it rise up,' contains a characteristic mark of the chief vital air, is untrue; for as the function of the vital air also ultimately rests on Brahman it can figuratively be ascribed to the latter. So Scripture also declares, 'No mortal lives by the breath that goes up and by the breath that goes down. We live by another in whom these two repose' (Ka. Up. II, 5, 5). Nor does the indication of the individual soul which you allege to occur in the passage, 'Let no man try to find out what speech is, let him know the speaker,' preclude the view of prâna denoting Brahman. For, as the passages, 'I am Brahman,' 'That art thou,' and others, prove, there is in reality no such thing as an individual soul absolutely different from Brahman, but Brahman, in so far as it differentiates itself through the mind (buddhi) and other limiting conditions, is called individual soul, agent, enjoyer. Such passages therefore as the one alluded to, (viz. 'let no man try to find out what speech is, let him know the speaker,') which, by setting aside all the differences due to limiting conditions, aim at directing the mind on the internal Self and thus showing that the
individual soul is one with Brahman, are by no means out of place. That the Self which is active in speaking and the like is Brahman appears from another scriptural passage also, viz. Ke. Up. I, 5, 'That which is not expressed by speech and by which speech is expressed that alone know as Brahman, not that which people here adore.' The remark that the statement about the difference of prâna and pragñâ (contained in the passage, 'Together they dwell in this body, together they depart') does not agree with that interpretation according to which prâna is Brahman, is without force; for the mind and the vital air which are the respective abodes of the two powers of cognition and action, and constitute the limiting conditions of the internal Self may be spoken of as different. The internal Self, on the other hand, which is limited by those two adjuncts, is in itself non-differentiated, so that the two may be identified, as is done in the passage 'prâna is pragñâ.'
The second part of the Sûtra is explained in a different manner also 1, as follows: Characteristic marks of the individual soul as well as of the chief vital air are not out of place even in a chapter whose topic is Brahman. How so? 'On account of the threefoldness of devout meditation.' The chapter aims at enjoining three kinds of devout meditation on Brahman, according as Brahman is viewed under the aspect of prâna, under the aspect of pragñâ, and in itself. The passages, 'Meditate (on me) as life, as immortality. Life is prâna,' and 'Having laid hold of this body it makes it rise up. Therefore let man worship it alone as uktha,' refer to the prâna aspect. The introductory passage, 'Now we shall explain how all things become one in that pragñâ,' and the subsequent passages, 'Speech verily milked one portion thereof; the word is its object placed outside;' and, 'Having by pragñâ taken possession of speech he obtains by speech all words &c.,' refer to the pragñâ aspect. The Brahman aspect finally is referred to in the following passage, 'These ten
objects have reference to pragñâ, the ten subjects have reference to objects. If there were no objects there would be no subjects; and if there were no subjects there would be no objects. For on either side alone nothing could be achieved. But that is not many. For as in a car the circumference of the wheel is set on the spokes and the spokes on the nave, thus are these objects set on the subjects and the subjects on the prâna.' Thus we see that the one meditation on Brahman is here represented as threefold, according as Brahman is viewed either with reference to two limiting conditions or in itself. In other passages also we find that devout meditation on Brahman is made dependent on Brahman being qualified by limiting adjuncts; so, for instance (Kh. Up. III, 14, 2), 'He who consists of mind, whose body is prâna.' The hypothesis of Brahman being meditated upon under three aspects perfectly agrees with the prâna chapter 1; as, on the one hand, from a comparison of the introductory and the concluding clauses we infer that the subject-matter of the whole chapter is one only, and as, on the other hand, we meet with characteristic marks of prâna, pragñâ, and Brahman in turns. It therefore remains a settled conclusion that Brahman is the topic of the whole chapter.
103:1 Imam sarîram instead of idam sarîram
104:1 Pañka sabdâdayah pañka prithivyâdayas ka dasa bhûtamâtrâh pañka buddhîndriyâni pañka buddhaya iti dasa pragñâmâtrâh. Yadvâ gñânendriyârthâh pañka karmendriyârthâs ka pañketi dasa bhûtamâtrâh dvividhânîndriyâni pragñâmâtrâ daseti bhâvah. Ân. Gi.
105:1 Viz. by the vrittikâra.
106:1 Ihâpi tad yugyate explaining the 'iha tadyogât' of the Sûtra.