The Concise Oxford Dictionary of World Religions (2576 page)

a
kara.
Radhakrishnan
, in his work
The Principal Upani
ads
(1953), included eighteen. The central teaching of these early upani
ads is that the Self (
tman
) is identical to the ultimate ground of reality (
Brahman
). He who realizes this finds liberation (
mok
a
) from the cycle of suffering (
sa
s
ra
) embodied in birth, death and rebirth. This speculative perspective, extolling the way of knowledge (jñ
nam
rga), became a point of departure for much of Indian philosophy, particularly the various schools of Ved
nta. The later Upani
ads, composed under Pur
ic,
Tantric
, or devotional influences, are less philosophical and more sectarian. Their importance is not so much for the history of philosophy in India as for an understanding of its popular religion.
The major Upani