Ramanujacharya's Brahma Sutra Bhashya translated By George Thibaut
SriBhashya - Ramanuja's Commentary On Brahma Sutra (Vedanta Sutra)

8. Neither air nor function, on account of its being stated separately.

Is this main vital breath nothing else but air, the second of the elements? Or is it a certain motion of the air? Or is it air that has assumed some special condition?--The first alternative may be adopted, on account of the text 'prâna is air.'--Or, since mere air is not called breath, while this term is generally applied to that motion of air which consists in inhalation and exhalation, we may hold that breath is a motion of air.--Of both these views the Sûtra disposes by declaring 'not so, on account of separate statement.' For in the passage 'From him there is produced breath,mind,and all sense-organs,ether and air,' &c, breath and air are mentioned as two separate things. For the same reason breath also cannot be a mere motion or function of air; for the text does not mention any functions of fire and the other elements, side by side with these elements, as separate things (and this shows that breath also cannot, in that text, be interpreted to denote a function of air). The text 'prâna is air,' on the other hand, intimates (not that breath is identical with air. but) that breath is air having assumed a special form, not a thing altogether different from it, like fire. In ordinary language, moreover, the word breath does not mean a mere motion but a substance to which motion belongs; we say,'the breath moves to and fro in inhalation and exhalation.'

Is breath, which we thus know to be a modification of air, to be considered as a kind of elementary substance, like fire, earth, and so on? Not so, the next Sûtra replies.