Brahma Knowledge, by L. D. Barnett, , at sacred-texts.com
§ 19. The Subtle Body.—According to the later Vedānta, the Soul in its wanderings from birth to birth is accompanied by the sense-organs and "breaths" as sums of potential faculties, and has for its vehicle the "subtle body," sūkshmaśarīra. The latter consists of portions of the five elements in their higher suprasensual form, and thus is as it were a seed which on occasion grows by the accession of gross matter into a physical body.
There is no clear evidence for the existence of
this idea in the Upanishads until the mention of a linga (the term used in the Sānkhya school for "subtle body") in B.A. IV. iv. 6; cf. Kaṭh. VI. 8, Śvet. VI. 9, Maitr. VI. 10. For Śankara's view see especially on Brahma-sūtra, III. i. 1 f., IV. ii. 6 f. The "subtle body" adheres to the soul until it attains perfect enlightenment and release in Brahma; the souls which never reach this goal are always attended by it.