Śaṅkaraon Brahma Sūtra 2.4.12

The chief vital air has its specific effect for that reason also that in scripture it is designated as having five functions, prS;/a, apiina, vydna, udana, samana. This distinction of functions is based on a distinction of effects. Prd«a is the forward-function whose work is aspiration, &c.; ap&na is the backward-function whose work is inspiration, &c.; vyiina is that which, abiding in the junction of the two, is the cause of works of strength ^ ; uddna is the ascending function and is the cause of the passing out (of the soul) ; sarnSna is the function which conveys the juices of the food equally through all the limbs of the body. Thus the prd;/a has five functions just as the mind (manas) has. The five functions of the mind are the five well-known ones caused by the ear, &c., and having sound and so on for their objects. By the functions of the mind we cannot here understand those enumerated (in Br/. Up. I, 5, 3), 'desire, representation,’ &c., because those are more than five.—But on the former explanation also there exists yet another function of the mind which does not depend on the ear, &c., but has for its object the past, the future, and so on ; so that on that explanation also the number five is exceeded.—Well, let us then follow the principle that the opinions of other (systems) if unobjectionable may be adopted, and let us assume that the five functions of the manas are those five which are known from the Yoga.ydstra, viz. right knowledge, error, imagination, slumber, and remembrance. Or else let us assume that the Sdtra quotes the manas as an analogous instance merely with reference to the plurality (not the fivefoldness) of its functions.—In any case the Sutra must be construed to mean that the prawa’s subordinate position with regard to the soul follows from its having five functions like the manas.