The Philosophy of the Upanishads c5.s2.1

c5.s2.1

As the Brâhmaṇas formed the ritual text-books of the Vedic S'âkhâs, so the Upanishads attached to them were originally nothing more that the text-books of dogma, a fact which accounts especially for the identity in them all of the fundamental thought, which is developed at greater or less length and with the utmost variety. The earliest rise of the S'akhas or Vedic schools, on which this community of the ritual, and with it the philosophical tradition depends, is to be sought in a time in which the contents of the Samhitâ were already substantially fixed, and were transmitted from teacher to pupil to be committed to memory.²