the Common Era. Indologist and Sanskrit scholar Patrick Olivelle states, "we have the two late prose Upanisads, the Prasna and the Mandukya, which cannot be much older than the beginning of the common era". Mahony, (writing for the MacMillan Encyclopedia of Religion) on the other hand, states that Mandukya Upanishad probably emerged in the late fifth and early fourth centuries BCE, along with Prashna and Maitri Upanishads. Phillips lists Mandukya Upanishad before and about the time the Shvetashvatara Upanishad, the Maitri Upanishad, as well as the first Buddhist Pali and Jaina canonical texts were composed. R D Ranade posits a view similar to Phillips, placing Mandukya's chronological composition in the fifth, that is the last group of ancient Principal Upanishads. Chronological roots The foundation of several theories in the Mandukya Upanishad are found in chronologically more ancient Sanskrit texts. For example, chapters 8.7 through 8.12 of Chandogya Upanishad discuss the "four states of consciousness" as awake, dream-filled sleep, deep sleep, and beyond deep sleep. Authorship The text of the Mandukya Upanishad is fully incorporated in the Mandukya Karika, a commentary attributed to the 6th century CE Gaudapada, and is not known to exist independent of this commentary. Isaeva states that some scholars, including Paul Deussen, presumed that Gaudapada may be its author; however, there is no historical or textual evidence for this hypothesis. Scholars consider Mandukya Upanishad as a Principal Upanishad with more ancient origins. Structure In contrast to the older Upanishads, the Mandukya Upanishad is very short, with clear and concise formulations. It has twelve short prose paragraphs. Contents The Mandukya Upanishad is an important Upanishad in Hinduism, particularly to its Advaita Vedanta school. It succinctly presents several central doctrines, namely that "the universe is Brahman," "the Self (Atma) exists and is Brahman," and "the four states of consciousness". The Mandukya Upanishad also presents several theories about the syllable Aum, and that it symbolizes self. Aum in the Mandukya Upanishad The Mandukya Upanishad opens by declaring, "Aum!, this syllable is this whole world". Thereafter it presents various explanations and theories on what it means and signifies. This discussion is built on a structure of "four fourths" or "fourfold", derived from A + U + M + "silence" (or without an element). Aum as all states of time In verse 1, the Upanishad states that time is threefold: the past, the present and the future, that these three are "Aum".