Upanishads

Upanishads is from the Sanskrit upaniṣad (Devanagari: उपनिषद्), built from upa (near), ni (down), and the root sad (to sit)[1]. The literal image is sitting down near a teacher, the classical setting for the philosophical instruction these texts record[1]. Some traditional interpreters read the term as also implying secret or esoteric teaching transmitted in close instruction[2]. The texts are typically dated from roughly 800 to 200 BCE, with later additions across many centuries[2].

their philosophical density means they are often best approached with commentary rather than as isolated quotations.

The Upanishads form the philosophical conclusion (anta) of the Vedas, and the tradition that focuses on them is named Vedanta (end of the Vedas)[3]. They contain dialogues, parables, and dense philosophical inquiry into the nature of reality (Brahman), the self (atman), and their relationship[3]. The most studied Upanishads are sometimes called the principal Upanishads, including the Brihadaranyaka, Chandogya, Aitareya, Kena, Katha, Isha, Mundaka, Mandukya, Prashna, Taittiriya, and Shvetashvatara[3].

Within Hindu philosophy, the Upanishads serve as the source text for the major Vedanta schools (Advaita, Vishishtadvaita, Dvaita, and others), each of which generates its own commentary tradition (bhashya) interpreting the same passages in different ways[4]. The famous mahavakyas (great sayings) such as Tat tvam asi (That thou art) and Aham Brahmasmi (I am Brahman) condense Upanishadic teaching into pithy formulas that have been the focus of intensive philosophical analysis[5].

Beyond technical philosophy, the Upanishads have shaped Hindu devotion, ethics, and worldview at the broadest level[2]. The Bhagavad Gita summarizes and develops Upanishadic teaching in narrative form; modern Indian thinkers including Vivekananda, Aurobindo, and Radhakrishnan have presented Upanishadic philosophy to global audiences[4].

Modern academic study of the Upanishads dates from 19th century European Orientalism and continues through Patrick Olivelle's careful translations and the work of many other Indologists[1]. Comparative philosophy of religion has placed Upanishadic thought in conversation with Greek philosophy, Christian mysticism, and modern Western metaphysics, with figures including Arthur Schopenhauer historically taking deep interest[2]. Religious studies emphasizes both the internal diversity of the Upanishadic corpus and the centrality of these texts to Hindu philosophical tradition[1].

• The Upanishadsby Eknath Easwaran (translator)
  primary source
• The Early Upanisads: Annotated Text and Translationby Patrick Olivelle
  book