Indian philosophy is generally discussed in terms of six major orthodox (Astika) schools, and three major heterodox (Nastika) schools. These words normally convey a division into theists and atheists. However, this is not the meaning implied when these terms are used to denote the Schools of Indian Philosophy. Orthodox (Astika) systems are those that accept the authority (Pramanattvam of the Vedas as a valid means of knowledge) of the Vedas, whereas heterodox (Nastika) systems are those who reject it. (The rejection was more due the i) inability of a person to grow during the same lifetime, ii) the Himsa involved in some of the rituals which shocked the sensitivity of both Mahavira and the Buddha.) The orthodox systems are the Sad-Darsanas, the six systems of Indian Philosophy- Nyaya, Vaisesika, Samkhya, Yoga, Mimamsa, and Vedanta. The heterodox systems are, Carvaka, Jainism, and Buddhism.
The Vedic corpus that is accepted as Pramana by the Astika philosphies has four sections – Samhita, Brahmana, Aranyaka, and Upanisads. Samhita has Suktas or Hymns. Brahmana contains the technical know-how of the fire-ritual. Aranyaka has Mantra and Upasanas that are practiced in the forests (that is, not for Grhasthas). Upanisads normally appear in the last part of Aranyaka and deal with spiritual philosophy. Some Upanisads are exceptions and appear in Samhita (Isavasya Upanisad is the 40th chapter of the Sukla-Yajurveda Samhita) and Brahmana (Prasna, Mundaka and Mandukya Upanisads are in the Gopatha Brahmana of Atharvaveda (Paippalada-Sakha) also.
Thus Upanisads, as they appear in the last part of the Vedas, are called Vedanta. There are 108 Upanisads, out of which ten are famous. Since Upanisad are mostly philosophical, they are found in prose. However, there are Upanisads like Taittiriyonisad and Ganapatyatharvasirsop? 9;ad and Isavasyopanisad that have Svaras.
These four sections are mapped to the four Asramas. A Brahmacari is supposed to study the Samhita. A Grhastha is supposed to follow the Brahmana. A Vanaprasthi is supposed to follow Aranyaka. A Samnyasiis supposed to study the Upanisads.
(To be continued)..