Śaṅkaraon Brahma Sūtra 3.3.8

Here it might be said that after all the unity of the two vidyas discussed must be admitted, since they are called by one and the same name, viz. ‘ the science of the udgitha.* —But this argument is of no avail against what has been said under the preceding Sutra. The decision there advo- cated has the advantage of following the letter of the revealed text ; the name ‘ udgitha-vidya ’ on the other hand is not a part of the revealed text, but given to the vidyds for convenience sake by ordinary men for the reason that the word ‘ udgitha * is met with in the text.— More- over, we observe that admittedly separate meditations such as the two mentioned under the last Sdtra have one and the same name. Similarly altogether separate sacrificial performances, such as the agnihotra, the dar.rapfinmmdsa, and so on, are all comprised under the one name Kd///aka, merely because they are recorded in the one book called — Ka///aka. Where, on the other hand, there is no special reason for assuming the difference of vidyds, their unity may be declared on the ground of identity of name ; as, e. g. in the case of the Sawvargavidyds.