Yoga is discussed in the ancient foundational Sutras of Hindu philosophy. The Vaiśeṣika Sūtra of the Vaisheshika school of Hinduism, dated to have been composed sometime between 6th and 2nd century BCE discusses Yoga.[note 14] According to Johannes Bronkhorst, an Indologist known for his studies on early Buddhism and Hinduism and a professor at the University of Lausanne, Vaiśeṣika Sūtra describes Yoga as "a state where the mind resides only in the soul and therefore not in the senses". This is equivalent to pratyahara or withdrawal of the senses, and the ancient Sutra asserts that this leads to an absence of sukha (happiness) and dukkha (suffering), then describes additional yogic meditation steps in the journey towards the state of spiritual liberation.
The first known appearance of the word "yoga", with the same meaning as the modern term, is in the Katha Upanishad, probably composed between the fifth and third century BCE, where it is defined as the steady control of the senses, which along with cessation of mental activity, leading to a supreme state.[note 13] Katha Upanishad integrates the monism of early Upanishads with concepts of samkhya and yoga. It defines various levels of existence according to their proximity to the innermost being Ātman. Yoga is therefore seen as a process of interiorization or ascent of consciousness. It is the earliest literary work that highlights the fundamentals of yoga. White states:
One of the earliest and most influential sub-traditions of Vedanta, is Advaita Vedanta, which posits nondualistic monism. This tradition emphasizes Jñāna yoga (yoga of knowledge), which is aimed at realizing the identity of one's atman (soul, individual consciousness) with Brahman (the Absolute consciousness). The most influential thinker of this school is Adi Shankara (8th century), who wrote various commentaries and original works which teach Jñāna yoga. In Advaita Vedanta, Jñāna is attained on the basis of scripture (sruti) and one's guru and through a process of listening (sravana) to teachings, thinking and reflecting on them (manana) and finally meditating on these teachings (nididhyāsana) in order to realize their truth. It is also important to develop qualities such as discrimination (viveka), renunciation (virāga), tranquility, temperance, dispassion, endurance, faith, attention and a longing for knowledge and freedom ('mumukṣutva).' Yoga in Advaita is ultimately a "meditative exercise of withdrawal from the particular and identification with the universal, leading to contemplation of oneself as the most universal, namely, Consciousness".
Yoga as exercise was created in what has been called the Modern Yoga Renaissance by the blending of Western styles of gymnastics with postures from Haṭha yoga in India in the 20th century, pioneered by Shri Yogendra and Swami Kuvalayananda. Before 1900 there were few standing poses in Haṭha yoga. The flowing sequences of salute to the Sun, Surya Namaskar, were pioneered by the Rajah of Aundh, Bhawanrao Shrinivasrao Pant Pratinidhi, in the 1920s. Many standing poses used in gymnastics were incorporated into yoga by Krishnamacharya in Mysore from the 1930s to the 1950s. Several of his students went on to found influential schools of yoga: Pattabhi Jois created Ashtanga Vinyasa Yoga, which in turn led to Power Yoga; B. K. S. Iyengar created Iyengar Yoga, and systematised the canon of asanas in his 1966 book Light on Yoga; Indra Devi taught yoga to many film stars in Hollywood; and Krishnamacharya's son T. K. V. Desikachar founded the Krishnamacharya Yoga Mandalam in Chennai. Other major schools founded in the 20th century include Bikram Choudhury's Bikram Yoga and Swami Sivananda of Rishikesh's Sivananda Vedanta Schools of Yoga. Modern yoga spread across America and Europe, and then the rest of the world.
Alexander Wynne observes that formless meditation and elemental meditation might have originated in the Upanishadic tradition. The earliest reference to meditation is in the Brihadaranyaka Upanishad, one of the oldest Upanishads. Chandogya Upanishad describes the five kinds of vital energies (prana). Concepts used later in many yoga traditions such as internal sound and veins (nadis) are also described in the Upanishad. Taittiriya Upanishad defines yoga as the mastery of body and senses.
According to Crangle, some researchers have favoured a linear theory, which attempts "to interpret the origin and early development of Indian contemplative practices as a sequential growth from an Aryan genesis",[note 4] just like traditional Hinduism regards the Vedas to be the ultimate source of all spiritual knowledge.[note 5] Thomas McEvilley favors a composite model where pre-Aryan yoga prototype existed in the pre-Vedic period and its refinement began in the Vedic period.
The early Buddhist texts describe yogic and meditative practices, some of which the Buddha borrowed from the śramaṇa tradition. The Pali canon contains three passages in which the Buddha describes pressing the tongue against the palate for the purposes of controlling hunger or the mind, depending on the passage. However, there is no mention of the tongue being inserted into the nasopharynx as in true khecarī mudrā. The Buddha used a posture where pressure is put on the perineum with the heel, similar to even modern postures used to stimulate Kundalini. Some of the major suttas that discuss yogic practice include the Satipatthana sutta (Four foundations of mindfulness sutta) and the Anapanasati sutta (Mindfulness of breathing sutta).
"...[T]here is the cultivation of meditative and contemplative techniques aimed at producing what might, for the lack of a suitable technical term in English, be referred to as 'altered states of consciousness'. In the technical vocabulary of Indian religious texts such states come to be termed 'meditations' ([Skt.:] dhyāna / [Pali:] jhāna) or 'concentrations' (samādhi); the attainment of such states of consciousness was generally regarded as bringing the practitioner to deeper knowledge and experience of the nature of the world." (Gethin, 1998, p. 10.)
Classical yoga incorporates epistemology, metaphysics, ethical practices, systematic exercises and self-development techniques for body, mind and spirit. Its epistemology (pramana) and metaphysics is similar to that of the Sāṅkhya school. The metaphysics of Classical Yoga, like Sāṅkhya, is mainly dualistic, positing that there are two distinct realities. These are prakriti (nature), which is the eternal and active unconscious source of the material world and is composed of three gunas, and the puruṣas (persons), the plural consciousnesses which are the intelligent principles of the world, and are multiple, inactive and eternal witnesses. Each person has a individual puruṣa, which is their true self, the witness and the enjoyer, and that which is liberated. This metaphysical system holds that puruṣas undergo cycles of reincarnation through its interaction and identification with prakirti. Liberation, the goal of this system, results from the isolation (kaivalya) of puruṣa from prakirti, and is achieved through a meditation which detaches oneself from the different forms (tattvas) of prakirti. This is done by stilling one's thought waves (citta vritti) and resting in pure awareness of puruṣa.