The System of the Vedanta according to Badarayana's Brahma-Sutras and Cankara's Commentary c6.s5.t3.4

c6.s5.t3.4

For the theme of the Kāṭhaka-Up. Śaṅkara firstly infers that “the two” here either the organs of knowledge with Buddhi at their head and the individual soul, or the individual and the highest soul are to be understood (p. 179—181), then, that only the latter is permissible; for that which drinks fulfilment for its previous deeds, is undoubtedly the individual soul; and side by side with it only a kindred nature, therefore the highest soul, could be mentioned (p. 182, 3); that this dwells in the heart, is so often said in other places (p. 182, 5); that of it also it is said, it drinks, must not be taken literally, just as if it were said: “the people are carrying a parasol,” when only one of them is carrying it (p. 180, 12. 182, 9, and 3, 3, 34, p. 921, 7, where the subject is once more explained); they are called shadow and light, because the one is subject to Saṃsāra, the other being free from it, Saṃsāra itself existing only through Ignorance (p. 182, 11). The same contrast is found again not only in other passages of the Kāṭhaka-Up., but also in the verse [taken with changed meaning from Ṛigv. 1, 164, 20] of the Muṇḍaka-Up. 3, 1, 1 (= Śvet. 4, 6. 7):