Anātmatva — The Nature of What Is Not the Self
Anātmatva (from an- = not, ātman = self, -tva = the quality of) designates the character of entities that are entirely other than the ātmā — principally the physical body, the sense organs, the mind-body complex, and the objects of the material world. It is the ontological counterpart to ātmatva (the quality of being the self), and its correct understanding is considered a prerequisite for any progress in ātma-vicāra (inquiry into the self).
The body-self confusion is identified in Viśiṣṭādvaita as one of the most pervasive and consequential forms of viparīta-jñāna (inverted knowledge). When the jīva takes the body to be itself — feeling 'I am tall,' 'I am young,' 'I am hungry,' 'I am dying' in the literal sense — it is mistaking what belongs to the ātmā for the ātmā itself. The distinction is between the possessor and the possessed, the knower and the known, the self and its instrument. The body is anātman — it is the self's instrument but not the self.
The Upaniṣadic tradition approaches anātmatva through the classic 'neti neti' (not this, not this) inquiry: progressively identifying each layer of what is not the self — body, senses, vital breaths, mind, intellect — until the witnessing ātmā is recognised as distinct from all of them. Śrī Rāmānuja accepts this investigation but situates its result within his broader framework: the ātmā, once correctly identified as distinct from the body and all material instruments, is then seen to be the body of Bhagavān — so that the inquiry does not terminate in the bare self but in the recognition of the self's śeṣatva to Bhagavān.
Practically, the cultivation of anātmatva-jñāna is not a depreciation of the body but a correct assignment of roles. The body is precious as an instrument — it is the vehicle through which the jīva performs service, engages in sādhana, and encounters the grace of Bhagavān and the Ācārya. What is to be overcome is not the body itself but the false identification with it. When anātmatva is properly understood, the jīva lives lightly in the body, using it without being enslaved by it, caring for it without being governed by its demands — the disposition of one who knows what they truly are.