The teachers who first said neti neti, not this, not this, were not trying to define the self. They were doing the opposite: naming each candidate that came to mind, and taking it back.
You are the body.
You are the body. Not this: the body replaces itself cell by cell across a lifetime, and whatever is asking the question outlasts the replacing.
You are the breath.
You are the breath. Not this: the breath is only the body's most honest habit, in and out, indifferent to whether anyone is watching it.
You are the mind, its thoughts and its moods.
You are the mind, its thoughts and its moods. Not this: a mood arrives and leaves, and something notices both, and that something is not itself a mood.
You are the roles you carry, the name on the door, the title in the signature.
You are the roles you carry, the name on the door, the title in the signature. Not this: take the name away and the noticing continues.
You are, then, the noticing itself, pure and undivided.
Here the tradition stops calling it a claim to retract. It says you cannot stand outside awareness to observe it as an object, the way you observed the body and the moods a moment ago. This last sentence does not get struck through like the others, not because it survives as a description but because it stops working as one. Subject and object have nowhere left to stand apart. Neti neti is not a ladder to a final rung called Self. It is a method that runs out of things to remove, and what is left is not a description at all.
I want to be careful here, because it is tempting to reach for physics to validate this and call it settled. Resist that. Advaita is not a discovery about neurons. It is a discipline of attention with its own internal logic, and it does not need a laboratory's authority to be worth taking seriously on its own terms.
But there is a family resemblance worth naming, carefully, as analogy and nothing more. Science, at its most honest, does not claim to prove its theories true. It claims to have not yet found the experiment that breaks them. A theory survives by surviving, the way an animal that has escaped every trap so far is still, technically, only escaped so far. One influential account of what makes a claim scientific at all says it only earns the name if you can state in advance what result would kill it. Gravity is a serious theory not because someone proved it true, but because someone could imagine, and go looking for, the falling apple that refuses to fall.
Newtonian mechanics describes the motion of everything, always, exactly.
Newtonian mechanics describes the motion of everything, always, exactly. Not this: the orbit of Mercury drifted from the prediction by a small stubborn amount no adjustment inside the old frame explained. Not this: a photograph taken during a solar eclipse showed starlight bending around the sun by the wrong amount for the old theory to survive. Not this, not this, until a new frame in which gravity is not a force but a shape reproduced everything the old one got right, and this too.
Neither method arrives at a final positive statement that closes the case. The teacher does not conclude with a tidy definition of the self, negations exhausted. Physics does not conclude with a theory anyone is willing to call finished. Both keep the door open by insisting on the discipline of not this, refusing to let a comfortable but inadequate answer calcify into truth simply because nothing better has arrived yet.
Where the two part is exactly where it matters. Falsification aims outward, at a world anyone with the right instrument can measure and re-measure. Neti neti aims inward, at an inquiry only the one doing it can verify, in a way no second observer can check from outside. To collapse the two into a single method would flatten what makes each one work.
What is left, in both cases, after enough has been taken away, is not nothing. It is just no longer a sentence.