The Taittirīya Upaniṣad's own presentation of the Pañcakośa — five progressively subtler 'selves' nested within each other. Not a list of layers but a progressive inward inquiry leading to Ātman.
The second chapter of the Taittirīya describes five progressively subtler forms of the self, nested like Russian dolls — each one inside the previous, each one more interior.
The outermost is made of food: the physical body that grows from food, lives on food, and returns to the earth. Inside it is a self made of vital breath — the animating force that makes the food-body alive. Inside that is a self made of mind — the thinking, reacting, feeling mental activity. Inside that is a self made of intellect — the discriminating, deciding faculty. And innermost is a self made of bliss — the deep satisfaction of being, tasted most purely in dreamless sleep.
The inquiry is: which of these is the real self? The Upanishad's answer is given structurally: each successive sheath is described as the antara ātman — the inner self — of the one before it. The inner self of the food-body is the breath-body; the inner self of the breath-body is the mind-body; and so on. Each layer is real — it exists, it has its own form and functions. But each is also not-self in the sense that something more interior can be found within it.
What is most interior of all — the inner self of the bliss-body — is not given a fifth label to wrap around a sixth sheath. The inquiry stops. What is found is not another, subtler object. What is found is the awareness that was doing all the finding: Brahman, which is identical with Ātman.
The Taittirīya's own vocabulary at each stage is significant. Each sheath is described with the formula anyo 'ntara ātmā — "the other inner self." The word anyo (other) is crucial: each successive sheath is genuinely distinct from the previous one. The mind-body is a real entity that is distinct from the vital-breath body. Śaṅkara's commentary insists on this: the Pañcakośa is not a set of names for one thing seen from different angles. Each kośa is a real upādhi (limiting adjunct) that produces a real appearance of a distinct self.
The word ānandarasa (the essence of bliss) in 2.5.1 is Śaṅkara's key for the ānandamaya kośa. The bliss-body has the quality of bliss because it is the closest sheath to Brahman. But it is still a sheath — it arises in deep sleep when the grosser sheaths are resolved, and it resolves when waking returns. Ātman is the witness of its arising and passing.
The philosophical tension in the Pañcakośa teaching is the relationship between the vijñānamaya kośa (intellect-sheath) and the Ātman that witnesses it. The vijñānamaya is the faculty of discrimination — the faculty that performs the Pañcakośa inquiry itself. When the inquiry reaches its conclusion and the vijñānamaya is identified as another not-self, what performs the final act of recognition? Is it a subtler layer of intellect, or is the recognition itself the event of Ātman's self-revelation?
Śaṅkara's answer: the recognition is not an intellectual act performed by a further, subtler faculty. It is what happens when the intellectual search exhausts itself. The vijñānamaya kośa is the last instrument of inquiry; when it has completed its work, it becomes still, and in that stillness the self-luminous Ātman is not discovered as a new object but recognised as what was always already present — as the awareness in which even the vijñānamaya arose and was observed. This is why Śaṅkara insists that nididhyāsana (deep contemplation) is necessary after manana: the intellect must be stilled, not just satisfied.