definable in terms of anything else. Nothing, says
Yajnavalkya, has any value, meaning, or indeed reality except in
relation to this Self[183]. The whole world including the Vedas and
religion is an emanation from him. The passage at which Maitreyi
expresses her bewilderment is obscure, but the reply is more definite.
The Self is indestructible but still it is incorrect to speak of the
soul having knowledge and perception after death, for knowledge and
perception imply duality, a subject and an object. But when the human
soul and the universal Atman are one, there is no duality and no human
expression can be correctly used about the Atman. Whatever you say of
it, the answer must be _neti, neti_, it is not like that[184]; that is
to say, the ordinary language used about the individual soul is not
applicable to the Atman or to the human soul when regarded as identical
with it.

This identity is stated more precisely in another passage[185] where
first occurs the celebrated formula Tat tvam asi, That art Thou, or Thou
art It[186], _i.e._ the human soul is the Atman and hence there is no
real distinction between souls. Like Yajniavalkya's teaching, the
statement of this doctrine takes the form of an intimate conversation,
this time between a Brahman, Uddalaka Aruni, and his son Svetaketu who
is twenty-four years of age and having just finished his studentship is
very well satisfied with himself. His father remarks on his conceit and
says "Have you ever asked your teachers for that instruction by which
the unheard becomes heard, the unperceived perceived and the unknown
known?" Svetaketu enquires what this instruction is and his father
replies, "As by one lump of clay all that is made of clay is known, and
the change[187] is a mere matter of words, nothing but a name, the truth
being that all is clay, and as by one piece of copper or by one pair of
nail-scissors all that is made of copper or iron can be known, so is
that instruction." That is to say, it would seem, the reality is One:
all diversity and multiplicity is secondary and superficial, merely a
matter of words. "In the beginning," continues the father, "there was
only that which is, one without a second. Others say in the beginning
there was that only which is not (non-existence), one without a second,
and from that which is not, that which is was born. But how could that
which is be born of that which is not[188]? No, only that which is was
in the beginning, one o