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 Âtman and hence there is no real distinction between souls. Like Yâjñiavalkya's teaching, the statement of this doctrine takes the form of an intimate conversation, this time between a Brahman, Uddâlaka Âruṇi, and his son Śvetaketu 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?" Śvetaketu 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 only without a second. It thought, may I be many: may I have offspring. It sent forth fire." Here follows a cosmogony and an explanation of the constitution of animate beings, and then the father continues--"All creatures have their root in the Real, dwell in the Real and rest in the Real. That subtle being by which this universe subsists, it is the Real, it is the Âtman, and thou, Śvetaketu, art It." Many illustrations of the relations of the Âtman and the universe follow. For instance, if the life (sap) leaves a tree, it withers and dies. So "this body withers and dies when the life has left it: the life dies not." In the fruit of the Banyan (fig-tree) are minute seeds innumerable. But the imperceptible subtle essence in each seed is the whole Banyan. Each example adduced concludes with the same formula, Thou art that subtle essence, and as in the Bṛihad-Âraṇyaka salt is used as a metaphor. "'Place this salt in water and then come to me in the morning.' The son did so and in the morning the father said 'Bring me the salt.' The son looked for it but found it not, for of course it was melted. The father said, 'Taste from the surface of the water. How is it?' The son replied, 'It is salt.' 'Taste from the middle. How is it?' 'It is salt.' 'Taste from the bottom, how is it?' 'It is salt.' ... The father said, 'Here also in this body you do not perceive the Real, but there it is.