The Upanishads (; singular: , IAST: , ; plural: ) are a collection of texts in the Vedic Sanskrit language which contain the earliest emergence of some of the central religious concepts of Hinduism, some of which are shared with Buddhism and Jainism. The Upanishads are considered by Hindus to contain revealed truths (Sruti) concerning the nature of ultimate reality (brahman) and describing the character and form of human salvation (moksha). The Upanishads are sometimes referred to as Vedanta (“Last part of Veda”) when interpreted in the context of Uttara Mimamsa. But according to the Brahmasutra, the Upanishads address a different subject matter (inquisition into Brahman), and the subject matter of the Vedas is inquisition into ritual action. Most interpretations of the Brahmasutra are clear that one does not have to master the Vedas first to study the Upanishads. Hence the Vedas and Upanishads are different, even though they share the same language (just like a book on history and a book on science may share the same language). To call them purely Vedanta would not be exactly right because they are really the source of both the Samkhya and later Vedanta philosophies. 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. The mukhya Upanishads are found mostly in the concluding part of the Brahmanas and Aranyakas and have been passed down in oral tradition. They all predate the Common Era, possibly from the Pre-Buddhist period (6th century BCE) down to the Maurya period. The remainder, known as the Muktika canon was mostly composed during medieval Hinduism, and new Upanishads continued being composed in the early modern and modern era, down to at least the 20th century. Along with the Bhagavad Gita and the Brahmasutra the mukhya Upanishads (known collectively as the Prasthanatrayi), provide a foundation for the several later schools of Vedanta, among them, two influential monistic schools of Hinduism. With the translation of the Upanishads in the early 19th century they also started to attract attention from a western audience. Schopenhauer was deeply impressed by the Upanishads and called it “the production of the highest human wisdom”. The 19th century transcendentalists noted the influence of Upanishads in the western philosophy.