The school of philosophical thought known as the Vedanta is also called Uttara-mimamsa. The founder of the Vedanta system of philosophy was Badarayana Vyasa. The founder of Purva-mimamsa school was Jaimini, the disciple of Sri Vyasa. Of these two, Purva-mimamsa is generally understood to imply the inquiry into the Mantra portion of the Vedas, while Uttara-mimamsa is understood to mean an inquiry into the Upanishad portion of the Vedas. In other words, Purva-mimamsa treats of Karma Kanda; Uttara-mimamsa deals with Jnana Kanda. The Brahma Sutras of Badarayana or Sri Vyasa are termed as the Vedanta Darshana. They are called by this name, because they are based upon the Upanishads, the end or the final part of the Veda. These Brahma Sutras are the outcome of the harmonising of the apparently conflicting Upanishadic texts by Badarayana. The Bhashya written by Sri Sankaracharya on the Brahma Sutras is known as Sariraka Bhashya.
The Vedas, each of which has a Samhita, Brahmana, Aranyaka and Upanishad, are again subdivided into two parts viz., the Karma Kanda or the work-portion and the Jnana Kanda or the knowledge-portion. The former leads man to world by happiness and enjoyment in Svarga or heaven and the latter to Moksha or liberation. The Samhita and the Brahmana sections go to make up the Karma Kanda and the Aranyaka and the Upanishad sections form the Jnana Kanda. Brahma Vidya or that knowledge by which the Brahman is attained is dealt with in the Upanishads. The Upanishads as the final part of the Vedas are Vedanta, the end of the Vedas. Through the divisions of Rig Veda and others, the Vedas are said to be four in number. Their branches are many. So also the Upanishads. In Rig Veda, there are twenty one branches. There are 109 branches in Yajur Veda. There are 1000 branches in Sama Veda. There are fifty branches in Atharvana Veda. In each branch there is one Upanishad.
The word Upanishad is formed by adding the Krip suffix and the prefixes Upa and Ni to the root Shad meaning (1) to shatter or kill, (2) to attain and (3) to loosen. By the word Upanishad is denoted the knowledge of the knowable entity inculcated by the work which is to be commented upon. By what etymological process this knowledge is denoted by the term Upanishad is now explained. This knowledge is called Upanishad by virtue of its signification that it shatters or destroys the seed of Samsara such as ignorance and the rest, in those seekers after emancipation, who, devoid of all desires for objects seen and heard of, acquire the knowledge called Upanishad to be hereafter explained, and with their mind firmly concentrated therein meditate on it; for it will also be said later on well ascertaining that he will be freed from the jaws of death or the knowledge of Brahman is called Upanishad because of the fact that it leads to Brahman, in that it makes the seekers after emancipation just above described attain the highest Brahman; for it will be said later on, having attained the Brahman he becomes untainted and immortal; or, even the knowledge of Agni is denoted by the term Upanishad, because of its connection with the meaning of the root, to loosen; for, the knowledge of Agni, the first born, the knower, born of Brahman the subject matter of the second of the boons asked for leads to the attainment of heaven and thus loosens or enfeebles the lot of misery; such as residence in the womb, birth, old age, etc., continually recurring in this world. It will also be said later on, having reached heaven, they enjoy Immortality. It may be argued that students apply the term Upanishad even to the book, as when they say, we shall study or teach the Upanishad. This is no fault, as the meaning of the root Shad, i.e., the killing of the cause of Samsara, etc., cannot be attached to the mere work but is attached to knowledge; and even the mere work may also be denoted by that word, because it serves the self-same purpose, as when it said ghee verily is life. The word Upanishad therefore is used in its primary sense when it is used to denote knowledge; but it is used by courtesy, i.e., in a secondary sense to denote the work. Thus by the mere analytical explanation of the word Upanishad, those who are fully competent to acquire knowledge have been stated. The whole subject matter of knowledge has also been stated to be the thorough release from the bondage of Samsara consisting in the attainment of the Brahman.
The meaning of the Upanishad may be either because it lessens the numerous evils of conception, birth, old age, disease, etc., in persons who take kindly to this knowledge of Brahman and approach it with faith and devotion, or because it makes them reach Brahman, or because it totally destroys the cause of Samsara such as ignorance, etc., thus from the several meanings of the root Shad preceded by Upani.
Sri Rama says to Hanuman: The only means by which the final emancipation is attained is through Mandukya Upanishad alone, which is enough for the salvation of all aspirants. If Jnana is not attained thereby, by the study of ten Upanishads thou shalt soon attain Jnana and then My seat. O son of Anjana, if thy Jnana is not made firm, study well the 32 Upanishads. Thou shalt get release. If thou longest after Videha Mukti, study the 108 Upanishads.
The Upanishads are the mystic experiences of the Rishis. The Upanishads, the Gita and the Brahma Sutras are technically called the Prasthanatraya. These are the three authoritative books on Hindu Philosophy. Any teacher who claims himself as an Acharya and who wants to open a new school of thought must write a commentary on these three important books. All the previous Acharyas, Sri Sankara, Ramanuja and Madhva have written commentaries on these books.