With this adhyâya begins the real Upanishad, best known under the name of the Aitareya-upanishad, and often separately edited, commented on, and translated. If treated separately, what we call the fourth adhyâya of the second Âranyaka, becomes the first adhyâya of the Upanishad, sometimes also, by counting all adhyâya from the beginning of the Aitareya-âranyaka, the ninth. The divisions adopted by Sâyana, who explains the Upanishad as part of the Âranyaka, and by Sankara, who explains it independently, vary, though Sâyana states that he follows in his commentary on the Upanishad the earlier commentary of Sankara. I have given the divisions adopted by Sâyana, and have marked those of Sankara's by figures in parentheses, placed at the end of each paragraph. The difference between this Upanishad and the three preceding adhyâyas is easily perceived. Hitherto the answer to the question, Whence this world? had been, From Prâna, prâna meaning breath and life, which was looked upon for a time as a sufficient explanation of all that is. From a psychological point of view this prâna is the conscious self (pragñâtman); in a more mythological form it appears as Hiranyagarbha, “the golden germ,” sometimes even as Indra. It is one of the chief objects of the prânavidyâ, or life-knowledge, to show that the living principle in us is the same as the living principle in the sun, and that by a recognition of their identity and of the true nature of prâna, the devotee, or he who has rightly meditated on prâna during his life, enters after death into the world of Hiranyagarbha.
This is well expressed in the Kaushîtaki-upanishad III, 2, where Indra says to Pratardana: “I am Prâna; meditate on me as the conscious self (pragñâtman), as life, as immortality. Life is prâna, prâna is life. Immortality is prâna, prâna is immortality. By prâna he obtains immortality in the other world, by knowledge (pragñâ) true conception. Prâna is consciousness (pragñâ), consciousness is prâna.”
This, however, though it may have satisfied the mind of the Brahmans for a time, was not a final solution. That final solution of the problem not simply of life, but of existence, is given in the Upanishad which teaches that Âtman, the Self, and not Prâna, Life, is the last and only cause of everything. In some places this doctrine is laid down in all its simplicity. Our true self, it is said, has its true being in the Highest Self only. In other passages, however, and nearly in the whole of this Upanishad, this simple doctrine is mixed up with much that is mythological, fanciful, and absurd, arthavâda, as the commentators call it, but as it might often be more truly called, anarthavâda, and it is only towards the end that the identity of the self-conscious self with the Highest Self or Brahman is clearly enuntiated.
Adoration to the Highest Self Hari, Om!
2. He thought: “Shall I send forth worlds?” (1) He sent forth these worlds,
3. Ambhas (water), Mariki (light), Mara (mortal), and Ap (water).
4. That Ambhas (water) is above the heaven, and it is heaven, the support. The Marikis (the lights) are the sky. The Mara (mortal) is the earth, and the waters under the earth are the Ap world. (2)
5. He thought: “There are these worlds; shall I send forth guardians of the worlds?”
Nostrils burst forth. From the nostrils proceeded scent (prâna), from scent Vayu (air).
Eyes burst forth. From the eyes proceeded sight, from sight Aditya (sun).
Ears burst forth. From the ears proceeded hearing, from hearing the Dis (quarters of the world).
Skin burst forth. From the skin proceeded hairs (sense of touch), from the hairs shrubs and trees.
The heart burst forth. From the heart proceeded mind, from mind Kandramas (moon).
The navel burst forth. From the navel proceeded the apana (the down-breathing), from apana death.
The generative organ burst forth. From the organ proceeded seed, from seed water. (4)
 Before the creation. Comm.
 Blinking, mishat, i. e. living; cf. Rv. X, 190, 2, visvasya mishato vasî, the lord of all living. Sâyana seems to take mishat as a 3rd pers. sing.
 The names of the four worlds are peculiar. Ambhas means water, and is the name given to the highest world, the waters above the heaven, and heaven itself. Marîkis are rays, here used as a name of the sky, antariksha. Mara means dying, and the earth is called so, because all creatures living there must die. Ap is water, here explained as the waters under the earth. The usual division of the world is threefold, earth, sky, and heaven. Here it is fourfold, the fourth division being the water round the earth, or, as the commentator says, under the earth. Ambhas was probably intended for the highest heaven (dyaus), and was then explained both as what is above the heaven and as heaven itself, the support. If we translate, like Sankara and Colebrooke, “the water is the region above the heaven which heaven upholds,” we should lose heaven altogether, yet heaven, as the third with sky and earth, is essential in the Indian view of the world.
 Purusha; an embodied being, Colebrooke; a being of human shape, Röer; purushâkâram virâtpindam, Sâyana.
 According to the commentator, from the five elements, beginning with water. That person is meant for the Virâg.
 Tap, as the commentator observes, does not mean here and in similar passages to perform austerities (tapas), such as the Krikkhra, the Kândrâyana, &c., but to conceive and to will and to create by mere will. I have translated it by brooding, though this expresses a part only of the meaning expressed by tap.
 Literally, was opened.
 Three things are always distinguished here—the place of each sense, the instrument of the sense, and the presiding deity of the sense.
 Prâna, i. e. ghrânendriya, must be distinguished from the prâna, the up-breathing, one of the five prânas, and likewise from the prâna as the principle of life.
 The Apâna, down-breathing, is generally one of the five vital airs which are supposed to keep the body alive. in our place, however, apâna is deglutition and digestion, as we shall see in II, 4, 3, 10.