A small Upaniṣad belonging to the Atharvaveda with just three sections in prose, it deals with three kinds of ‘puruṣas’ or beings, called ‘ātmā’. The first is the physical body comprising the various limbs and subject to birth and death. It is the ‘bāhyātmā’ or the outer ātman. The second, called ‘antarātmā,’ the inner ātman, is the mind composed of the sūkṣma-bhūtas or the subtle elements and responsible for the functions of the senses as also the various states like thinking, feeling and willing. The third and the last is the ‘paramātmā’ or the ‘puruṣa,’ the Supreme Self or the Person. He is the true Self who is subtler than the subtlest, beyond all change and destruction, the eternally pure witness of all, the infinite, the indestructible.
Some texts contain an additional part in verses numbering 31, describing this Ātman-Brahman, the unreal nature of the manifested world and the state of liberation of the emancipated being.