The Aitareya Upanishad (Sanskrit: ऐतरेय उपनिषद् IAST ) is a Mukhya Upanishad, associated with the Rigveda. It comprises the fourth, fifth and sixth chapters of the second book of Aitareya Aranyaka, which is one of the four layers of Rig vedic text. Aitareya Upanishad discusses three philosophical themes: first, that the world and man is the creation of the Atman (Universal Self); second, the theory that the Atman undergoes threefold birth; third, that Consciousness is the essence of Atman. Chronology According to a 1998 review by Patrick Olivelle and other scholars, the Aitareya Upanishad was likely composed in a pre-Buddhist period, possibly 6th to 5th century BCE. Discussion Aitareya Upanishad is a primary ancient Upanishad, and is listed as number 8 in the Muktika canon of 108 Upanishads. Considered one of the middle Upanishads, the date of composition is not known but has been estimated by scholars to be sometime around 6th or 5th century BCE. The Aitareya Upanishad is a short prose text, divided into three chapters, containing 33 verses. First chapter In the first chapter of the Aitareya Upanishad, Atman is asserted to have existed alone prior to the creation of the universe. It is this Atman, the Self or the Inner Self, that is then portrayed as the creator of everything from itself and nothing, through heat. The text states that the Atman created the universe in stages. First came four entities: space, maram (earth, stars), maricih (light-atom) and apas (ur-water, cosmic fluid). After these came into existence, came the cosmic self and eight psyches and principles (speech, in-breathing, sight, hearing, skin/hair, mind, out-breathing, reproductivity). Atman then created eight guardians corresponding to these psyches and principles. Then, asserts Aitareya Upanishad, came the connective principles of hunger and thirst, where everything became interdependent on everything else through the principle of apana (digestion). Thereafter came man, who could not exist without a sense of Self and Atman. But this sense then began cogitating on itself, saying that "I am more than my sensory organs, I am more than my mind, I am more than my reproductive ability", and then asked (abridged), Paul Deussen summarizes the first chapter of Aitareya Upanishad as follows, Second chapter In the second chapter, Aitareya Upanishad asserts that the Atman in any man is born thrice: first, when a child is born (procreation); second, when the child has been cared for and loved to Selfhood