Yoga philosophy is one of the six major orthodox schools of Hindu philosophy, though it is only at the end of the first millennium CE that Yoga is mentioned as a separate school of thought in Indian texts, distinct from Samkhya. Ancient, medieval and most modern literature often refers to Yoga-philosophy simply as Yoga. A systematic collection of ideas of Yoga is found in the Yoga Sutras of Patanjali, a key text of Yoga which has influenced all other schools of Indian philosophy.
The metaphysics of Yoga is Samkhya's dualism, in which the universe is conceptualized as composed of two realities: Puruṣa (witness-consciousness) and Prakṛti (nature). Jiva (a living being) is considered as a state in which puruṣa is bonded to Prakṛti in some form, in various permutations and combinations of various elements, senses, feelings, activity and mind. During the state of imbalance or ignorance, one or more constituents overwhelm the others, creating a form of bondage. The end of this bondage is called liberation, or mokṣa, by both the Yoga and Samkhya schools of Hinduism, and can be attained by insight and self-restraint.
The ethical theory of Yoga-philosophy is based on Yamas and Niyama, as well as elements of the Guṇa theory of Samkhya. The epistemology of Yoga-philosophy, like the Sāmkhya school, relies on three of six Pramanas as the means of gaining reliable knowledge. These include Pratyakṣa (perception), Anumāṇa (inference) and Sabda (Āptavacana, word/testimony of reliable sources). Yoga-philosophy differs from the closely related non-theistic/atheistic Samkhya school by incorporating the concept of a "personal, yet essentially inactive, deity" or "personal god" (Ishvara).
History
Yoga-practice
The origins of yoga-practice are unclear, but seems to have developed in ascetic milieus in the first millennium BCE. Some of its earliest discussions and of proto-Samkhya ideas are found in 1st millennium BCE Indian texts such as the Katha Upanishad, the Shvetashvatara Upanishad and the Maitri Upanishad.
The root of the word "Yoga" is found in hymn 5.81.1 of the Rig Veda, a dedication to rising Sun-god in the morning (Savitri), interpreted as "yoke" or "yogically control".
The Rig Veda, however, does not describe Yoga philosophy with the same meaning or context as in medieval or modern times. Early references to practices that later became part of Yoga-philosophy, are made in Brihadaranyaka Upanishad, the oldest Upanishad. Gavin Flood translates it as, "...having become calm and concentrated, one perceives the self (atman), within oneself." The practice of pranayama (consciously regulating breath) is mentioned in hymn 1.5.23 of Brihadaranyaka Upanishad (), and the practice of pratyahara (withdrawal of the senses) is mentioned in hymn 8.15 of Chandogya Upanishad ().
The Katha Upanishad, dated to be from about the middle of the 1st millennium BCE, in verses 2.6.6 through 2.6.13 recommends a path to Self-knowledge akin to Samkhya, and calls this path Yoga.
Yoga-practice is also mentioned in foundational texts of other orthodox schools such as the Vaisesikha Sutras, Nyaya Sutras and Brahma Sutras.
Separate darsana
Yoga as a separate school of thought is mentioned in Indian texts from the end of the 1st millennium CE. The systematic collection of ideas of the Yoga school of Hinduism is found in the Yoga Sutras of Patanjali. After its circulation in the first half of the 1st millennium CE, many Indian scholars reviewed it, then published their Bhāṣya (notes and commentary) on it, which together form a canon of texts called the Pātañjalayogaśāstra ("The Treatise on Yoga of Patañjali"). Yoga as a separate school of philosophy has been included as one of the six orthodox schools in medieval era Indian texts; the other schools are Samkhya, Nyaya, Vaisheshika, Mimamsa and Vedanta. According to Bryant,