The philosopher and commentator Shankara is thought to have composed commentaries on eleven mukhya or principal Upanishads, those that are generally regarded as the oldest, spanning the late Vedic and Mauryan periods. The Muktika Upanishad (predates 1656) contains a list of 108 canonical Upanishads Chapter: VEDIC LITERATURE AND UPANISHADS. p. 19: "..according to the Vedas to which they are supposed to belong, ... The muktika list of 108 upanishad is as follows:" and lists itself as the final one. Dara Shikoh (d. 1659), son of the Mughal emperor Shah Jahan, translated fifty Upanishads into Persian. Max Müller (1879) was aware of 170. Sadhale, in his massive verse index IAST: Upaniṣad-vākya-mahā-kośa, has drawn on 223 different extant texts that call themselves by this name. Additionally, parts of earlier texts, of Brahmanas or passages of the Vedas themselves, are sometimes considered Upanishads.

Etymology

The Sanskrit term IAST: upaniṣad derives from upa- (nearby), ni- (at the proper place, down) and sad, that is "sitting down near" a teacher in order to receive instruction - "laying siege" to the teacher, as Schayer puts it. Monier-Williams adds that "according to native authorities upanishad means 'setting to rest ignorance by revealing the knowledge of the supreme spirit');..." A gloss of the term IAST: upaniṣad based on Shankara's commentary on the IAST: Kaṭha and IAST: Bṛhadāraṇyaka Upanishads equates it with Ātmavidyā, that is "knowledge of the Self", or Brahmavidyā "knowledge of Brahma".Fact: date=April 2007 Other dictionary meanings include "esoteric doctrine" and "secret doctrine".

Philosophy

The Upanishads speak of a universal spirit (Brahman) and an individual soul, (Atman) and at times assert the identity of both. Brahman is the ultimate, both transcendent and immanent, the absolute infinite existence, the sum total of all that ever is, was, or shall be. The mystical nature and intense philosophical bent of the Upanishads has led to their explication in numerous manners, giving birth to three main schools of Vedanta. Shankara's exegesis of the Upanishads does not describe Brahman as the God in a monotheistic sense; he ascribes to it no limiting characteristics, not even those of being and non-being.Fact: date=April 2007 Thus, Shankara's philosophy is named advaita, "not two" as opposed to dvaita, founded by Madhvacharya, which holds that Brahman is ultimately a personal God, to be aligned with Vishnu, or Krishna (brahmano hi pratisthaham, I am the Foundation of Brahman Bhagavad Gita 14.27). The third major school of Vedanta is Vishishtadvaita, founded by Ramanujacharya and it has some aspects in common with the other two.