Brahma Knowledge, by L. D. Barnett, , at sacred-texts.com
§ 15. Phases of the Self.—The highest existence is thus Thought without thinking, the state in which the soul has no consciousness of any external object, or indeed of any object at all, strictly speaking, for it is itself in conscious identity with the sum of all being or Universal Idea; "whilst he seeth not a thing, yet doth he see, though he see not the thing erstwhile to be seen. He that hath sight loseth not his sight, for it is imperishable. But there is naught beside
him, naught apart from him, that he may see" (B.A. IV. iii. 23).
The only analogy that experience furnishes for this supposed condition of soul is that of dreamless sleep; and it was inferred that in such sleep the soul is actually in this transcendent state.
Besides this, the earlier Upanishads recognise two other states of the soul, waking and dreaming. When awake the soul puts forth out of itself a world of sense and organs of sense and empirical thought, and renders itself the subject of the experiences conjured up by them. In dreaming sleep the sense-organs swoon away and are absorbed into the manas, the organ forming the centre of empirical cognition and will (§ 18), which thus has now the vision of the world as it is reflected from the waking state; at the same time the "life-breaths," prāṇas, are active as in waking.
The later Upanishads assume yet another phase, which they call the "Fourth" (turīya, chaturtha). In this the soul, transcending dreamless sleep, is absolutely wakeful in its union with the universal subject of thought, and exercises in perfect stillness an infinite real consciousness of all in the Self which is different in kind from the "unconscious consciousness" ascribed to dreamless sleep.
The waking, dreaming, and dreamless phases are respectively termed Vaiśvānara ("common to all mankind"), Taijasa ("luminous," for in
dreams the soul is its own light, B.A. IV. iii. 9), and Prājna ("intelligent," for in deep sleep the Self is one with the Universal Idea or "intelligent Self," prājna ātmā, B.A. IV. iii. 21); these terms do not occur until Māṇḍ. iii. ff. On dreaming sleep see also B.A. II. i. 18 (soul wanders about within the body), IV. iii. 9-14 (two accounts, in one of which soul leaves the body, while in the other it remains in it), iii. 20 f., Ch. VIII. x. 2, Pra. IV. 2 f. Dreamless sleep, B.A. IV. iii. 19-33, Ch. VIII. vi. 3, x.-xi. Fourth State, Māṇḍ. VII., Maitr. VI. 19, VII. 11, Māṇḍūkya-kārikā I. 12-16, III. 33 f. See also Śankara on Brahma-sūtra I. iii. 19 f., 40 f., III. ii. 1 f. Śankara, following Ch. IV. iii. 3, holds that in deep sleep, in which the soul is in temporary identity with Brahma, the functions of sense, together with the manas, in which they are absorbed, are merged in the "breaths" travelling through the pericardium and veins (cf. § 18), while the soul becomes one with the Brahma residing under "determinations" in the heart (in B.A. II. i. 19, it rests in the pericardium, in Ch. VIII. vi. 3 in the veins). The statement of Ch. VIII. xii. 3, that "the Calm (samprasāda), rising from this body, wins to the Supreme Light, and shows itself in its own form; this is the highest spirit (purusha)" is taken by Śankara (on Brahma-sūtra IV. iv. 1 f.) as referring to the soul not in dreamless sleep, but in its final release from the body after enlightenment (see § 24); this "own form" is the existence
of the soul in its absolute selfhood, where there is no longer a distinction between individual and universal soul. For the theories of the Vedānta after Śankara see above, § 12.