Six Classical Schools in Hindu Philosophy

Question

I have been reading about the six classical schools of Hindu philosophy (also known as the Shad-Darshan system). Did all of these schools exist simultaneously and debate with each other (thereby being equally valid perspectives)? Or was there a gradual evolution of these schools (where Nyaya was the original progenitor and Vedanta became the crowning achievement and thereby most valid perspective)?

Answer 1

In his Introduction to his translation of the Brahma Sutras, Swami Vireswarananda writes, pp ii-iii, available here - http://www.wisdomlib.org/hinduism/book/brahma-sutras/d/doc62753.html:

In the age immediately preceding Buddha and during his lifetime there was a great religious and philosophical upheaval in India. From the Brahma-jâla-Sutras we learn that in his time there wrere as many as sixty-two different schools of philosophy in India. We also learn from Buddhistic literature the names of a good number of teachers who were venerated in Âryâvarta at the time—names like Purâna Kasyapa, Kâtyâyana, Makkâli Gosâla, Nigantha Nâthaputra, the founder of Jainism, and others. While these great souls represented Indian culture from an anti-Vedic standpoint there were many great names that represented the culture from the traditional standpoint—names that are still venerated by Hindu religion and culture.

The destructive criticism of everything in the old system by the Chârvâkas and others set the orthodox section to organize their belief on a more rationalistic basis and render it immune against all such criticism. This led to the foundation of the six systems of orthodox Hindu philosophy—orthodox[1] in the sense that they accepted the authority of the Vedas in things transcendental—while there were others who did not accept this authority and therefore were dubbed heterodox, though otherwise they too were the outcome of Upanishadic thought. The acceptance of the authority of the Vedas by these orthodox schools, however, does not mean that they accepted them in toto . Their allegiance to the Vedas varied widely and often it was too loose. Of the six orthodox schools, viz. Nyâya, Vaiseshika, Sânkhya, Yoga, Purva Mimâmsâ and Uttara Mimâmsâ or Vedanta, the last two are intimately connected with the Vedas, which is one of the reasons why they are not mentioned in the Jaina and Buddhistic literature, while the others are mentioned.

These six orthodox systems of thought developed side by side at different intellectual centres, of which there were a good number all over the country even during the Upanishadic period. Again in each system there were shades of difference. Thus for centuries philosophic thought developed in India till at last it became so unwieldy that a regular systematization of each school of thought was found a great necessity. This led to the Sutra literature.