Hindu philosophy
Authors: Clear Edeltraud Harzer 
Published: September 2018

Hindu philosophy is the longest surviving philosophical tradition in India. We can recognize several historical stages. The earliest, from around 700 bc, was the proto-philosophical period, when karma and liberation theories arose, and the proto-scientific ontological lists in the Upaniṣads were compiled. Next came the classical period, spanning the first millennium ad, in which there was constant philosophical exchange between different Hindu, Buddhist and Jaina schools. During this period, some schools, such as Sāṅkhya, Yoga and Vaiśeṣika, fell into oblivion and others, such as Kashmir Saivism, emerged. Finally, after the classical period only two or three schools remained active. The political and economic disturbances caused by repeated Muslim invasions hampered intellectual growth. The schools that survived were the Logic school (Nyāya), especially New Logic (Navya-Nyāya), the grammarians and, above all, the Vedānta schools.
The central concerns of the Hindu philosophers were metaphysics, epistemological issues, philosophy of language, and moral philosophy. The different schools can be distinguished by their different approaches to reality, but all considered the Vedas (the sacred scriptures) authoritative, and all believed that there is a permanent individual self (ātman). They shared with their opponents (Buddhists and Jainas) a belief in the need for liberation. They used similar epistemic tools and methods of argument.
In contrast to their opponents, who were atheists, Hindu philosophers could be either theists or atheists. Actually we can observe an increased tendency towards theistic ideas near the end of the classical period, with the result that the strictly atheistic teachings, which were more philosophically rigorous and sound, fell into disuse. Hindu metaphysics saw ātman as part of a larger reality (Brahman).
Because these views of the world differed, they had to be proved and properly established. Accordingly, logical and epistemological tools were developed and fashioned according to the needs and beliefs of individual philosophers. Most agreed on two or three sources of knowledge: perception and inference, with verbal testimony as a possible third. In this quest for philosophical rigour, there was a need for precision of language, and there were important philosophical developments among the grammarians and the philosophers who explained the Vedas (the Mīmāṃsakas). A culmination of these linguistic efforts can be seen in the philosopher of language Bhartṛhari. One of his greatest accomplishments was the full articulation of the theory that a sentence as a whole is understood in a sudden act of comprehension.
It is customary to name six Hindu schools, of the more than a dozen that existed, thus lumping several into a single school. This is particularly the case with Vedānta. The six are listed in three pairs: Sāṅkhya–Yoga; Vedānta–Mīmāṃsā; Nyāya–Vaiśeṣika. This does not take account of the grammarians or Kashmir Saivism.
In their quest for freedom from rebirth, all the Hindu schools operated within the same framework. Their ultimate goal was liberation. How much they were truly engaged in the quest for liberation apart from their philosophical preoccupations is not always clear, yet they never doubted its real possibility.