The Upanishads are also known by another name Vedanta, as they are believed to be the last portions of the Vedas (veda-anta, end); it is by this name that the philosophy of the Upanishads, the Vedanta philosophy, is so familiar to us. A modern student knows that in language the Upanishads approach the classical Sanskrit; the ideas preached also show that they are the culmination of the intellectual achievement of a great epoch.

As they thus formed the concluding parts of the Vedas they retained their Vedic names which they took from the name of the different schools or branches (shakha) among which the Vedas were studied (1). Thus the Upanishads attached to the Brahmanas of the Aitareya and Kaushitaki schools are called respectively Aitareya and Kaushitaki Upanishads. Those of the Tandins and Talavakaras of the Sama-veda are called the Chandogya and Talavakara (or Kena) Upanishads. Those of the Taittiriya school of the Yajurveda form the Taittiriya and Mahanarayana, of the Katha school the Kathaka, of the Maitrayani school the Maitrayani. The Brihadaranyaka Upanishad forms part of the Shatapatha Brahmana of the Vajasaneyi schools. The Isha Upanishad also belongs to the latter school. But the school to which the Shvetashvatara belongs cannot be traced, and has probably been lost. The presumption with regard to these Upanishads is that they represent the enlightened views of the particular schools among which they flourished, and under whose names they passed. A large number of Upanishads of a comparatively later age were attached to the Atharva-Veda, most of which were named not according to the Vedic schools but according to the subject-matter with which they dealt (2).

It may not be out of place here to mention that from the frequent episodes in the Upanishads in which the Brahmins are described as having gone to the Kshattriyas for the highest knowledge of philosophy, as well as from the disparateness of the Upanishad teachings from that of the general doctrines of the Brahmanas and from the allusions to the existence of philosophical speculations amongst the people in Pali works, it may be inferred that among the Kshattriyas in general there existed earnest philosophic enquiries which must be regarded as having exerted an important influence in the formation of the Upanishad doctrines. There is thus some probability in the supposition that though the Upanishads are found directly incorporated with the Brahmanas it was not the production of the growth of Brahmanic dogmas alone, but that non-Brahmanic thought as well must have either set the Upanishad doctrines afoot, or have rendered fruitful assistance to their formulation and cultivation, though they achieved their culmination in the hands of the Brahmins.

1: When the Samhita texts had become substantially fixed, they were committed to memory in different parts of the country and transmitted from teacher to pupil along with directions for the practical performance of sacrificial duties. The latter formed the matter of prose compositions, the Brahmanas. These however were gradually liable to diverse kinds of modifications according to the special tendencies and needs of the people among which they were recited. Thus after a time there occurred a great divergence in the readings of the texts of the Brahmanas even of the same Veda among different people. These different schools were known by the name of particular Shakhas (e.g. Aitareya, Kaushitaki) with which the Brahmanas were associated or named. According to the divergence of the Brahmanas of the different Shakhas there occurred the divergences of content and the length of the Upanishads associated with them.
2: Garbha Upanishad, Atman Upanishad, Prashna Upanishad, etc. There were however some exceptions such as the Mandukya, Jabala, Paingala, Shaunaka, etc.

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