The Upanishads

More than 200 Upanishads are known, of which the first dozen or so are the oldest and most important and are referred to as the principal or main (mukhya) Upanishads.ThemukhyaUpanishads are found mostly in the concluding part of theBrahmanasandAranyakasand were, for centuries, memorized by each generation and passed downorally.

The early Upanishads all predate the Common Era, fiveof them in all likelihood pre-Buddhist (6th century BCE),down to theMaurya period.Of the remainder, some 95 Upanishads are part of theMuktikacanon, composed from about the last centuries of 1st-millennium BCE through about 15th-century CE.New Upanishads, beyond the 108 in the Muktika canon, continued to be composed through the early modern and modern era,though often dealing with subjects which are unconnected to the Vedas.

Along with theBhagavad Gitaand theBrahmasutra, themukhyaUpanishads (known collectively as thePrasthanatrayi)provide a foundation for the several later schools ofVedanta, among them, two influentialmonisticschools of Hinduism. With the translation of the Upanishads in the early 19th century they also started to attract attention from a western audience.Arthur Schopenhauerwas deeply impressed by the Upanishads and called it "the production of the highest human wisdom".The 19th-centurytranscendentalistsnoted the influence of the Upanishads in western philosophy.