II, 4, 19

The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896] at sacred-texts.com

19. And on account of the difference of characteristics.

There is moreover a difference of characteristics between the chief prâna and the other prânas. When speech &c. are asleep, the chief prâna alone is awake. The chief prâna alone is not reached by death, while the other prânas are. The staying and departing of the chief prâna--not that of the sense-organs--is the cause of the maintenance and the destruction of the body. The sense-organs, on the other hand, are the cause of the perception of the sense-objects, not the chief prâna. Thus there are manifold differences distinguishing the prâna from the senses, and this also shows the latter to be different in being from the prâna--To infer from the passage, 'thereupon they all assumed his form,' that the sense-organs are nothing but prâna is wrong, because there also an examination of the context makes us understand their difference. For there the sense-organs are enumerated first ('Voice held, I shall speak,' &c.); after that it is said that speech, &c. were seized by death in the form of weariness ('Death having become weariness held them back; therefore speech grows weary'); finally prâna is mentioned separately as not having been overcome by death ('but death did not seize the central breath'), and is

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asserted to be the best ('he is the best of us'). The assuming of the form of prâna has therefore, in accordance with the quoted passages, to be understood to mean that the energizing of speech and so on depends on the prâna, but not that they are identical with it.--Hence it follows that the word 'prâna is applied to the sense-organs in a secondary sense. Thus Sruti also says, 'Thereupon they all assumed his form, and therefore they are called after him prânas;' a passage declaring that the word prâna, which properly refers to the chief prâna is secondarily applied to the sense-organs also. Speech and the other sense-organs are therefore different in being from the prâna.