Uddālaka Āruṇi sent his son Śvetaketu to the guru at the age of twelve. Study, he said. Come back when you know the Vedas.
Śvetaketu returned at twenty-four. He had studied for twelve years. He knew the four Vedas. He was proud. His father looked at him and saw the pride, and understood that the study had been incomplete.
He said — my son, have you asked for the teaching by which the unheard becomes heard, the unthought becomes thought, the unknown becomes known?
Śvetaketu said — no, father. What teaching is that?
Uddālaka said — bring me a fig from that banyan tree.
Śvetaketu brought it.
Break it open. What do you see?
Small seeds, sir.
Break one seed open. What do you see?
Nothing, sir.
Uddālaka said: that subtle nothing you cannot see — out of it the great banyan tree grows. The tree is real. But what makes the tree real is something you cannot see. That is the subtle essence. That is the Self of the whole banyan. Tat tvam asi, Śvetaketu. That art thou.
On another day he said — bring a pot of water. Put salt in it. Leave it overnight.
In the morning he said — bring me the salt.
Śvetaketu could not. The salt had dissolved.
Taste the water on the top.
Salt, sir.
Taste the water in the middle.
Salt, sir.
Taste the water at the bottom.
Salt, sir.
Uddālaka said: where is the salt? Can you find it anywhere? No. But is it there? Yes — everywhere. The salt is everywhere in the water, and you cannot isolate it anywhere. That is the Self. You cannot find it as a thing. It is the reality in which the things swim. Tat tvam asi, Śvetaketu. That art thou.
He repeated the teaching nine times over the chapter, with nine different analogies. The sleeping man in whom all perception dissolves. The bees that take nectar from many flowers and cannot tell whose flower the honey was from. The rivers that flow into the sea and no longer know which river they were. Each analogy points at the same thing. Each ends with the same words. Tat tvam asi — that art thou.
This is the most famous mahāvākya of the Upaniṣads. What the son's twelve years of study had not produced, his father gave him in nine conversations. The teaching was not new. Śvetaketu already was what the teaching was about. He only had to be shown, carefully, that he had been missing what was closest.