One medieval Indian catalogue counted sixteen schools, including one that prized mercury
Classical India produced a crowded marketplace of philosophies, sorted by whether they accepted the Vedas. The familiar count is six orthodox schools and five heterodox ones, but the scholar Vidyaranya listed sixteen, among them a grammarians' tradition built on sound and an alchemical school that treated mercury as a route to enlightenment.
Philosophical systems on the subcontinent are often called darshana, a word linked to seeing. Kautilya's Arthashastra preferred anvikshiki, critical investigation. Most major schools crystallised over a long span, starting around 500 BCE and running several centuries into the Common Era. Some of the oldest surviving texts are the Upanishads, composed in the later Vedic period between about 1000 and 500 BCE.
The usual dividing line is the authority of the Vedas. Schools that accepted it are labelled astika, those that rejected it nastika, though this sorting is a later scholarly construct and sources disagree about who belongs where. Among the orthodox, Nyaya specialised in logic and accepted four valid means of knowing, while Samkhya split reality into perceiving consciousness and the perceived world, a dualism that shaped much later thought. Vedanta, focused on the Upanishads, later fractured into sub-schools ranging from strict non-dualism to outright dualism. Vidyaranya, writing around 1374 to 1380, widened the map to include Shaiva traditions and a linguistic school whose thinker Bhartrhari placed speech at the heart of metaphysics.
The non-Vedic shramana movements argued about atoms, free will, materialism, non-violence and vegetarianism. Jainism and Buddhism proved the most influential, while Charvaka, Ajnana and the Ajivikas eventually died out. Jain thought is described as the oldest Indian philosophy to separate body and soul completely, teaching that each soul has infinite knowledge obscured by ignorance and karma. Historians outside the tradition place Mahavira in the 6th century BCE, near the Buddha's time, with his predecessor Parshvanatha some 250 years earlier, though Parshvanatha's biography remains debated.
Despite their quarrels, nearly all these schools share vocabulary: dharma, karma, rebirth, suffering and the goal of liberation, whether called moksha or nirvana. Yet the texts range well beyond salvation, into epistemology, value theory and metaphysics. The shramana ideas, including the Jain doctrine that truth looks different from different viewpoints, left marks on every later Indian tradition, which either absorbed them or pushed back.
Source: Indian philosophy
