In Hindu philosophy, turiya (Sanskrit: तुरीय, meaning "the fourth"), also referred to as chaturiya, chaturtha, is the true self (atman) beyond the three common states of consciousness (waking, dreaming, and dreamless deep sleep). It is postulated in several Upanishads and explicated in Gaudapada's Mandukya Karika.

Upanishads

Turiya as 'the fourth' is referred to in a number of proncipal Upanishads. One of the earliest mentions of the phrase turiya, "fourth," is in verse 5.14.3 of the Brihadaranyaka Upanishad (7th-6th century BCE), referring to a 'fourth foot' of the Gayatri Mantra, the first, second and third foot being the 24 syllables of this mantra:

According to Raju, chapter 8.7 through 8.12 of the Chandogya Upanishad (7th-6th century BCE) , though not mentioning turiya, 'anticipate' the Mandukya Upanishad and it's treatment of turiya. These verses of the Chandogya Upanishad set out a dialogue between Indra and Virocana, in search of atman, the immortal perceiver, and Prajapati, their teacher. After rejecting the physical body, the dream self, and the dreamless sleep (in which there is no perception of  Ï am") as atman, Prajapati declares in verse 12 to Indra that the mortal body is the abode of the "immortal and non-bodily self," which is the perceiver, the one who perceives due to the faculties of the senses. 

The phrase "turiya" also appears in Maitri Upanishad (late 1st millennium BCE) in sections 6.19 (in the context of yoga) and 7.11:

Verse 7 of the Mandukya Upanishad (1st-2nd century CE) refers to "the fourth" (caturtha), or "the fourth quarter," the first, second and third quarter being situated in the waking, dreaming and dreamless state:

Michael Comans disagrees with Nakamura's suggestion that "the concept of the fourth realm (caturtha) was perhaps influenced by the Sunyata of Mahayana Buddhism," stating 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."

According to Ellen Goldberg, this fourth quarter describes a state of meditation; the insight during meditation of Turiya is known as amātra, the 'immeasurable' or 'measureless' in the Mandukya Upanishad, being synonymous with samādhi in Yoga terminology.

Advaita Vedanta

Gaudapada

Gaudapada (ca. 7th century), an early guru in Advaita Vedanta, was the author or compiler of the , a commentary on the Māṇḍukya Upanishad, also known as the  and as the . Gaudapada was influenced by Buddhism, though he was a Vedantin and not a Buddhist. In the , Gaudapada deals with perception, idealism, causality, truth, and reality.  Gaudapada's commentary on verse 7 of the Mandukya Upanishad:

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). For Gaudapada, turiya is the "true 'state' of experience," in which the infinite (ananta) and non-different (advaita/abheda) are apprehended. 

Isaeva notes that the Mandukya Upanishad asserts that "the world of individual souls and external objects is just a projection of one indivisible consciousness (citta)," which is "identical with the eternal and immutable atman of the Upanisads [..] in contrast to momentary
vijnana taught by the Buddhist schools."

Adi Shankara
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):<ref group=web name=Om>[http://www.advaita.org.uk/discourses/downloads/om.pdf advaita.org.uk, ‘Om’ – three states and one reality (An interpretation of the Mandukya Upanishad)]</ref> 
 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)". 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)". 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)". This is the causal body.

Turiya is liberation, the autonomous realization of the non-causal Brahman beyond and underlying these three states.

Kashmir Shaivism

Kashmir Shaivism holds the state called turya – the fourth state. It is neither wakefulness, dreaming, nor deep sleep. In reality, it exists in the junction between any of these three states, i.e. between waking and dreaming, between dreaming and deep sleep, and between deep sleep and waking. In Kashmir Shaivism there exists a fifth state of consciousness called Turiyatita -  the state beyond Turiya.'' Turiyatita, also called the void or shunya  is the state where one attains liberation otherwise known as jivanmukti or moksha.

Based on the Tantraloka an extended model of seven consecutive stages of turiya is presented by Swami Lakshman Joo. These stages are called:
 Nijānanda
 Nirānanda
 Parānanda
 Brahmānanda
 Mahānanda
 Chidānanda
 Jagadānanda
While turiya stages 1 - 6 are attributed to the "internal subjective samādhi" (nimīlanā samādhi), once samādhi becomes permanently established in the seventh turiya stage it is described to span not only the internal subjective world anymore but beyond that also the whole external objective world (unimīlanā samādhi).

See also

Hinduism
 Brahma Samhita
 Rasa (theology)
 Rasa lila
 Samādhi
 Shuddhadvaita
Buddhism
 Mindfulness
 Dhyana in Buddhism
 Shikan-taza
 Mahamudra
 Dzogchen
 Sunyata
 Buddha-nature
 Two truths doctrine
Cross-over
 Choiceless awareness
Therapy
 Morita therapy
 Gestalt therapy
 Acceptance and commitment therapy

Notes

References

Sources
Printed sources

 

 
 

 

 
  Some editions spell the author Isayeva.

 

 
 

 
 

 

 

 
  
 
 

 

 

Web-sources

Hindu philosophical concepts
Vaishnavism
Nonduality
Advaita Vedanta