In Hindu philosophy, turiya (Sanskrit: तुरीय, meaning "the fourth") or caturiya, chaturtha, is pure consciousness. Scientists described it as a hypo-metabolic state of "restful alertness."  Turiya is the background that underlies and transcends the three common states of consciousness. The states of consciousness are: waking consciousness, dreaming, and dreamless sleep.[web 1][web 2]
Turiya is discussed in Verse 7 of the Mandukya Upanishad; however, the idea is found in the oldest Upanishads. For example, Chapters 8.7 through 8.12 of Chandogya Upanishad discuss the "four states of consciousness" as awake, dream-filled sleep, deep sleep, and beyond deep sleep. Similarly, Brihadaranyaka Upanishad, in chapter 5.14 discusses Turiya state, as does Maitri Upanishad in sections 6.19 and 7.11.
Verse VII of the Mandukya Upanishad describes Turiya:
Not inwardly cognitive, nor outwardly cognitive, not both-wise cognitive,
not a cognition-mass, not cognitive, not non-cognitive,
unseen, with which there can be no dealing, ungraspable, having no distinctive mark,
non-thinkable, that cannot be designated, the essence of assurance,
of which is the state of being one with the Self
the cessation of development, tranquil, benign, without a second,
such they think is the fourth. He is the Self (Atman). He should be discerned.— Mandukya Upanishad 7, 
Understanding of Turiya
Advaita posits three states of consciousness, namely waking (jagrat), dreaming (svapna), deep sleep (suṣupti), which are empirically experienced by human beings, and correspond to the Three Bodies Doctrine:
- The first state is the waking state, in which we are aware of our daily world. This is the gross body.
- The second state is the dreaming mind. This is the subtle body.
- The third state is the state of deep sleep. This is the causal body.
Advaita also posits the fourth state of Turiya, which some describe as pure consciousness, the background that underlies and transcends these three common states of consciousness.[web 1][web 2] Turiya is the state of liberation, where states Advaita school, one experiences the infinite (ananta) and non-different (advaita/abheda), that is free from the dualistic experience, the state in which ajativada, non-origination, is apprehended. According to Candradhara Sarma, Turiya state is where the foundational Self is realized, it is measureless, neither cause nor effect, all prevading, without suffering, blissful, changeless, self-luminous, real, immanent in all things and transcendent. Those who have experienced the Turiya stage of self-consciousness have reached the pure awareness of their own non-dual Self as one with everyone and everything, for them the knowledge, the knower, the known becomes one, they are the Jivanmukta.
Advaita traces the foundation of this ontological theory in more ancient Sanskrit texts. For example, chapters 8.7 through 8.12 of Chandogya Upanishad discuss the "four states of consciousness" as awake, dream-filled sleep, deep sleep, and beyond deep sleep. One of the earliest mentions of Turiya, in the Hindu scriptures, occurs in verse 5.14.3 of the Brihadaranyaka Upanishad. The idea is also discussed in other early Upanishads.
Gaudapada (ca. 7th century) was an early guru in the Advaita Vedanta. Gaudapada is traditionally said to have been the grand-guru of the great teacher, Adi Shankara, one of the most important figures in Hindu philosophy. Gaudapada is believed to be the founder of Shri Gaudapadacharya Math, and the author or compiler of the Māṇḍukya Kārikā.
Gaudapada wrote or compiled the Māṇḍukya Kārikā, also known as the Gauḍapāda Kārikā and as the Āgama Śāstra.[note 1] In this work, Gaudapada deals with perception, idealism, causality, truth, and reality. The fourth state, (turīya avasthā), corresponds to silence, as the other three correspond to AUM. It is the substratum of the other three states. It is, states Nakamura, atyanta-shunyata (absolute emptiness).
Michael Comans disagrees with Nakamura's thesis that "the fourth realm (caturtha) was perhaps influenced by the Sunyata of Mahayana Buddhism."[note 2] According to Comans,
It is impossible to see how the unequivocal teaching of a permanent, underlying reality, which is explicitly called the "Self", could show early Mahayana influence.
Comans further refers to Nakamura himself, who notes that later Mahayana sutras such as the Laṅkāvatāra Sūtra and the concept of Buddha-nature, were influenced by Vedantic thought. Comans concludes that
[T]here can be no suggestion that the teaching about the underlying Self as contained in the Mandukya contains shows any trace of Buddhist thought, as this teaching can be traced to the pre-Buddhist Brhadaranyaka Upanishad.
Isaeva states that there are differences in the teachings in the texts of Buddhism and the Mandukya Upanishad of Hinduism, because the latter asserts that citta "consciousness" is identical with the eternal and immutable atman "soul, self" of the Upanishads. In other words, Mandukya Upanishad and Gaudapada affirm the soul exists, while Buddhist schools affirm that there is no soul or self.
Adi Shankara described, on the basis of the ideas propounded in the Mandukya Upanishad, the three states of consciousness, namely waking (jågrata), dreaming (svapna), and deep sleep (susupti),[web 3][web 4] which correspond to the three bodies:
- The first state is that of waking consciousness, in which we are aware of our daily world. "It is described as outward-knowing (bahish-prajnya), gross (sthula) and universal (vaishvanara)".[web 4] This is the gross body.
- The second state is that of the dreaming mind. "It is described as inward-knowing (antah-prajnya), subtle (pravivikta), and burning (taijasa)".[web 4] This is the subtle body.
- The third state is the state of deep sleep. In this state, the underlying ground of consciousness is undistracted. "[T]he Lord of all (sarv’-eshvara), the knower of all (sarva-jnya), the inner controller (antar-yami), the source of all (yonih sarvasya), the origin and dissolution of created things (prabhav’-apyayau hi bhutanam)".[web 4] This is the causal body.
In the waking consciousness there is a sense of 'I' (self identity) and awareness of thoughts. In the sleep/dream state there is no or little sense of 'I'; however, there are thoughts and the awareness of thoughts. Waking and dreaming are not true experiences of Absolute Reality and metaphysical truth, because of their dualistic natures of subject and object, self and not-self, ego, and non-ego.
Kashmir Shaivism is a school of Śaivism consisting of Trika, the three goddesses Parā, Parāparā and Aparā, and its philosophical articulation in Pratyabhijña, a branch of Kashmir Shaivism. It is described by Abhinavagupta[note 3]as "paradvaita", meaning "the supreme and absolute non-dualism".[web 5]
The philosophy of Kashmir Shaivism can be seen in contrast to Shankara's Advaita. Advaita Vedanta holds that Brahman is inactive (niṣkriya) and the phenomenal world is an illusion (māyā). In Kashmir Shaivisim, all things are a manifestation of the Universal Consciousness, Chit or Brahman. Kashmir Shaivisim sees the phenomenal world (Śakti) as real: it exists, and has its being in Consciousness (Chit).
- Dhyana in Buddhism
- Two truths doctrine
- Nakamura notes that there are contradictions in doctrine between the four chapters.
- Nakamura, as cited in Comans 2000 p.98.
- Abhinavgupta (between 10th – 11th century AD) who summarized the view points of all previous thinkers and presented the philosophy in a logical way along with his own thoughts in his treatise Tantraloka.[web 5]
- PT Raju (1985), Structural Depths of Indian Thought, State University New York Press, ISBN 978-0887061394, pages 32-33; Quote: "We can see that this story [in Chandogya Upanishad] is an anticipation of the Mandukya doctrine, (...)"
- Robert Hume, Chandogya Upanishad - Eighth Prathapaka, Seventh through Twelfth Khanda, Oxford University Press, pages 268-273
- Hume, Robert Ernest (1921), The Thirteen Principal Upanishads, Oxford University Press, p. 392 footnote 11
- Hume, Robert Ernest (1921), The Thirteen Principal Upanishads, Oxford University Press, pp. 391–393 External link in
- Goldberg, Ellen (2002). Ardhanarishvara: The Lord who is Half Woman, p. 85
- Arvind Sharma (2004), Sleep as a State of Consciousness in Advaita Vedånta, State University of New York Press, page 3
- William Indich (2000), Consciousness in Advaita Vedanta, Motilal Banarsidass, ISBN 978-8120812512, pages 57-60
- Wilber 2000, p. 132.
- Arvind Sharma (2004), Sleep as a State of Consciousness in Advaita Vedånta, State University of New York Press, pages 15-40, 49-72
- King 1995, p. 300 note 140.
- Sarma 1996, pp. 122, 137.
- Sarma 1996, pp. 126, 146.
- Comans 2000, pp. 128-131, 5-8, 30-37.
- Indich 2000, pp. 106–108;
Bruce M. Sullivan (1997). Historical Dictionary of Hinduism. Scarecrow. pp. 59–60. ISBN 978-0-8108-3327-2.;
Bina Gupta (1998). The Disinterested Witness: A Fragment of Advaita Vedānta Phenomenology. Northwestern University Press. pp. 26–30. ISBN 978-0-8101-1565-1.
- PT Raju (1985), Structural Depths of Indian Thought, State University New York Press, ISBN 978-0887061394, pages 32-33
- Patrick Olivelle (1998). Upaniṣads. Oxford University Press. p. 77. ISBN 978-0-19-283576-5.;
Sanskrit (Wikisource): प्राणोऽपानो व्यान इत्यष्टावक्षराणि अष्टाक्षर ह वा एकं गायत्र्यै पदम् एतदु हैवास्या एतत् स यावदिदं प्राणि तावद्ध जयति योऽस्या एतदेवं पदं वेद अथास्या एतदेव तुरीयं दर्शतं पदं परोरजा य एष तपति यद्वै चतुर्थं तत्तुरीयम् दर्शतं पदमिति ददृश इव ह्येष परोरजा इति सर्वमु ह्येवैष रज उपर्युपरि तपत्य् एव हैव श्रिया यशसा तपति योऽस्या एतदेवं पदं वेद ॥ ३ ॥
- Indich 2000, pp. 58-67, 106-108.
- Potter 1981, p. 103.
- Nakamura 2004, p. 308.
- Nakamura 2004, p. 285.
- Comans 2000, p. 98.
- Isaeva 1993, p. 54.
- KN Jayatilleke (2010), Early Buddhist Theory of Knowledge, ISBN 978-8120806191, pages 246-249, from note 385 onwards;
Steven Collins (1994), Religion and Practical Reason (Editors: Frank Reynolds, David Tracy), State Univ of New York Press, ISBN 978-0791422175, page 64; Quote: "Central to Buddhist soteriology is the doctrine of not-self (Pali: anattā, Sanskrit: anātman, the opposed doctrine of ātman is central to Brahmanical thought). Expressed very briefly, this is the [Buddhist] doctrine that human beings have no soul, no self, no unchanging essence.";
Edward Roer (Translator), Shankara's Introduction, p. 2, at Google Books, pages 2-4
Katie Javanaud (2013), Is The Buddhist 'No-Self' Doctrine Compatible With Pursuing Nirvana?, Philosophy Now
- John C. Plott et al (2000), Global History of Philosophy: The Axial Age, Volume 1, Motilal Banarsidass, ISBN 978-8120801585, page 63, Quote: "The Buddhist schools reject any Ātman concept. As we have already observed, this is the basic and ineradicable distinction between Hinduism and Buddhism".
- Flood, Gavin. D. 2006. The Tantric Body. P.56,62,63,66,68,146
- Consciousness is Everything, The Yoga of Kashmir Shaivism, Swami Shankarananda pp. 56-59
- Pratyãbhijñahṛdayam, Jaideva Singh, Moltilal Banarsidass, 2008 p.24-26
- The Doctrine of Vibration: An Analysis of Doctrines and Practices of Kashmir Shaivism, By Mark S. G. Dyczkowski, p.44
- Ksemaraja, trans. by Jaidev Singh, Spanda Karikas: The Divine Creative Pulsation, Delhi: Motilal Banarsidass, p.119
- Mishra, K. Kashmir Saivism, The Central Philosophy of Tantrism, pp. 330-334
- Vijnanabhairava verse 109, dh 85, trans. by Jaidev Singh, p.98
- http://bhagavan-ramana.org/ramana_maharshi/books/tw/tw617.html Ramana Maharshi. States of Consciousness.
- Sri Chinmoy. Summits of God-Life.
- Arvind Sharma, Sleep as a State of Consciousness in Advaita Vedånta. State University of New York Press
- advaita.org.uk, ‘Om’ – three states and one reality (An interpretation of the Mandukya Upanishad)
- Piyaray L. Raina, Kashmir Shaivism versus Vedanta – A Synopsis
- Comans, Michael (2000). "The Method of Early Advaita Vedānta: A Study of Gauḍapāda, Śaṅkara, Sureśvara, and Padmapāda". Delhi: Motilal Banarsidass.
- Isaeva, Natalia (1993). Shankara and Indian Philosophy. Albany: State University of New York Press (SUNY). ISBN 978-0-7914-1281-7. Some editions spell the author Isayeva.
- Nakamura, Hajime (2004), A History of Early Vedanta Philosophy. Part Two, Delhi: Motilal Banarsidass Publishers Private Limited
- Nikhilananda, Swami (1974). Mandukyopanishad with Gaudapada’s Karika and Sankara’s Commentary. Mysore: Shri Ramakrishna Ashrama.
- Potter, Karl. H. (1981), Encyclopedia of Indian Philosophies: Advaita Vedānta up to Śaṃkara and his pupils, Volume 3, Delhi: Motilal Banarsidass, ISBN 81-208-0310-8
- Shankarananda, Swami (2006). The Yoga of Kashmir Shaivism: Consciousness Is Everything. Delhi: Motilal Banarsidass Publishers Private Limited.
- Sharma, C. (1997). A Critical Survey of Indian Philosophy. Delhi: Motilal Banarsidass. ISBN 81-208-0365-5.
- Wilber, Ken (2000), Integral Psychology, Shambhala Publications