The Cambridge History of India, Vol. I: Ancient India v1.c17.170

v1.c17.170

The same doctrine appears in another form in the Upanishads which are engaged with the discussion of the underlying reality. They agree in this that all reality in the ultimate issue must be reduced to one, called variously *brahman*, 'the holy power,' or *ātman*, 'the self.' Moreover, the Upanishads agree in regarding the absolute to be unknowable, and though they ascribe to it intelligence they deprive that term of meaning by emptying it of all thought. If the real is the absolute alone, the existence of the appearance of this world must be explained; but naturally enough the Upanishads do not successfully attempt this task; and it was not until the time of Çaṅkarāchārya in the beginning of the ninth century a.d. that it was found possible to reconcile the doctrines of the different texts by the view that all existence is merely illusion. This is perhaps a logical development of the doctrine of the Upanishads; but the Upanishads were groping after truth and did not attempt to deduce all the consequences of their guesses at the nature of reality.