A nondual philosophical or religious perspective or theory maintains that there is no fundamental distinction between mind and matter, or that the entire phenomenological world is an illusion (with reality being described variously as the Void, the Is, Emptiness, the mind of God, Atman or Brahman). Nontheism provides related conceptual and philosophical information.
Many traditions (generally originating in Asia) state that the true condition or nature of reality is nondualistic, and that these dichotomies are either unreal or (at best) inaccurate conveniences. While attitudes towards the experience of duality and self may vary, nondual traditions converge on the view that the ego, or sense of personal being, doer-ship and control, is ultimately said to be an illusion. As such many nondual traditions have significant overlap with mysticism.
Nondualism may also be viewed as a practice, namely the practice of self-inquiry into one's own being as set forth by Ramana Maharshi, which is intended to lead a person to realize the nondual nature of existence.
Nondualism can refer to one of two types of quality. One is the quality of union with reality, God, the Absolute. This quality is knowable and can be gained spontaneously and via practice of inquiry. A second quality is absolute by nature, or to put it in words, "conceptual absence of 'neither Yes nor No'," as Wei Wu Wei wrote. This latter quality is beyond the quality of union. It may be viewed as unknowable.
Accessibility is not relevant to the second quality mentioned in the paragraph above, since, according to that quality, an essential part of its gaining includes the realisation that the entire apparent existence of the individual who would gain access to understanding nondualism is in fact merely illusional. Achieving the second of these qualities therefore implies the extinguishing of the ego-sense that was seeking it:
The Western philosophical concept monism is similar to nondualism. Some forms of monism hold that all phenomena are actually of the same substance. Other forms of monism including attributive monism and idealism are similar concepts to nondualism. Nondualism proper holds that different phenomena are inseparable or that there is no hard line between them, but that they are not the same. The distinction between these two types of views is considered critical in Zen, Madhyamika, and Dzogchen, all of which are nondualisms proper. Some later philosophical approaches also attempt to undermine traditional dichotomies, with the view they are fundamentally invalid or inaccurate. For example, one typical form of deconstruction is the critique of binary oppositions within a text while problematization questions the context or situation in which concepts such as dualisms occur.
Nondualism superficially resembles solipsism, but from a nondual perspective solipsism mistakenly fails to consider subjectivity itself. Upon careful examination of the referent of "I," i.e. one's status as a separate observer of the perceptual field, one finds that one must be in as much doubt about it, too, as solipsists are about the existence of other minds and the rest of "the external world." (One way to see this is to consider that, due to the conundrum posed by one's own subjectivity becoming a perceptual object to itself, there is no way to validate one's "self-existence" except through the eyes of others -- the independent existence of which is already solipsistically suspect!) Nondualism ultimately suggests that the referent of "I" is in fact an artificial construct (merely the border separating "inner" from "outer," in a sense), the transcendence of which constitutes enlightenment.
It should be pointed out that technically, there can be no such thing as a nondual perspective or theory or experience, only a realization of Oneness or nonduality. One cannot accurately claim to experience nonduality, because the concept of experience depends on the subject-object distinction, which is a duality. The subject experiences an object, which is something separate from the subject. This is incompatible with a truly nondual realization. Thus, technically, there cannot truly be an accurate verbal account of this union, only words that insufficiently point to the realization.
Ken Wilber comments that nondual traditions:
Nisargadatta Maharaj, when asked how to tell when someone is approaching this understanding, commented:
Advaita (Sanskrit a, not; dvaita, dual) is a nondual tradition from India, with Advaita Vedanta, a branch of Hinduism, as its philosophical arm. The theory was first consolidated by Sri Adi Shankaracharya in the 8th century AD. Most smarthas are adherents to this theory of the nature of the soul (Brahman).
According to Ramana Maharshi, the jnani (one who has realised the Self) sees no individual ego, and does not regard himself (or anyone else) as a "doer" of actions. The state of recognition is called jnana which means "knowledge" or "wisdom" referring to the idea that in this state of being, one is constantly aware of the Self. Bob Adamson (Melbourne, Australia), once a student of Nisargadatta Maharaj, who belonged to the Navanath Sampradaya lineage, says that a 'Jnani' is the 'knowing presence' which abides with all (of us) yet this knowing is seemingly covered over by identification with the 'minds content'. Ramesh Balsekar comments that it is in order for phenomenae to occur, that the illusion of personal existence and doer-ship (ego) is present:
However, teachers like Adamson point to the fact that the content of the mind is known, recognized by a presence or awareness that is independent of the mind's content. Adamson teaches that we form an identity based on the content of the mind (feelings, sensations, hopes, dreams, thoughts), however our true identity or nature is that which observes all of these things - the seer, the witness or the Self.
In the Mahayana Buddhist canon, the Diamond Sutra presents an accessible nondual view of "self" and "beings", while the Heart Sutra asserts shunyata — the "emptiness" of all "form" and simultaneously the "form" of all "emptiness". The Lotus Sutra's parable of the Burning House implies that all talk of Duality or Non-Duality by Buddhas and Bodhisattvas is merely Skillful Means (Sanskrit upaya kausala) meant to lead the deluded to a much higher truth. The fullest philosophical exposition is the Madhyamaka; by contrast many laconic pronouncements are delivered as koans. Advanced views and practices are found in the Mahamudra and Maha Ati, which emphasize the vividness and spaciousness of nondual awareness.
Mahayana Buddhism, in particular, tempers the view of nonduality (wisdom) with respect for the experience of duality (compassion) — ordinary dualistic experience, populated with selves and others (sentient beings), is tended with care, always "now". This approach is itself regarded as a means to disperse the confusions of duality (i.e. as a path). In Theravada, that respect is expressed cautiously as non-harming, while in the Vajrayana, it is expressed boldly as enjoyment (especially in tantra).
Dzogchen is a relatively esoteric (to date) tradition concerned with the "natural state", and emphasizing direct experience. This tradition is found in the Nyingma tradition of Tibetan Buddhism, where it is classified as the highest of this lineage's nine yanas, or vehicles of practice. Similar teachings are also found in the non-Buddhist Bön tradition. In Dzogchen, the primordial state, the state of nondual awareness, is called rigpa.
The Dzogchen practitioner realizes that appearance and emptiness are inseparable. One must transcend dualistic thoughts to perceive the true nature of one's pure mind. This primordial nature is clear light, unproduced and unchanging, free from all defilements. One's ordinary mind is caught up in dualistic conceptions, but the pure mind is unafflicted by delusions. Through meditation, the Dzogchen practitioner experiences that thoughts have no substance. Mental phenomena arise and fall in the mind, but fundamentally they are empty. The practitioner then considers where the mind itself resides. The mind can not exist in the ever-changing external phenomena and through careful examination one realizes that the mind is emptiness. All dualistic conceptions disappear with this understanding.
Zen is a non-dual tradition. It can be considered a religion, a philosophy, or simply a practice depending on one's perspective. It has also been described as a way of life, work, and an art form. Zen practitioners deny the usefulness of such labels, calling them, "The finger pointing at the moon." Tozan, one of the founders of Soto Zen in China, had a teaching known as the Five Ranks of the Real and the Ideal, which points out the necessity of not getting caught in the duality between Absolute and Relative/Samsara and Nirvana, and describes the stages of further transcendence into fully realising the Absolute in all activities.
A Course in Miracles or ACIM is a modern day Christian non-dualistic teaching. This tradition states, "Nothing real can be threatened. Nothing unreal exists. Herein lies the peace of God.
Christian Science might also qualify as non-dualistic. In a glossary of terms written by the founder, Mary Baker Eddy, matter is defined as illusion and when defining individual identity she writes "There is but one I, or Us, but one divine Principle, or Mind, governing all existence".
The central doctrine of Sufism, sometimes called Wahdat-ul-Wujood or Wahdat al-Wujud or Unity of Being, is the Sufi understanding of Tawhid (the oneness of God; absolute monotheism). Put very simply, for Sufis, Tawhid implies that all phenomena are manifestations of a single reality, or Wujud (being), which is indeed al-Haq (Truth, God). The essence of Being/Truth/God is devoid of every form and quality, and hence unmanifest, yet it is inseparable from every form and phenomenon, either material or spiritual. It is often understood to imply that every phenomenon is an aspect of Truth and at the same time attribution of existence to it is false. The chief aim of all Sufis then is to let go of all notions of duality (and therefore of the individual self also), and realize the divine unity which is considered to be the truth.
Jalal ad-Din Muhammad Rumi, (1207-1273), one of the most famous Sufi masters and poets, has written that what humans perceive as duality is in fact a veil, masking the reality of the Oneness of existence. "All desires, preferences, affections, and loves people have for all sorts of things," he writes, are veils. He continues: "When one passes beyond this world and sees that Sovereign (God) without these 'veils,' then one will realize that all those things were 'veils' and 'coverings' and that what they were seeking was in reality that One." The veils, or rather, duality, exists for a purpose, however, Rumi contends. If God as the divine, singular essence of all existence were to be made fully manifest to us, he counsels, we would not be able to bear it and would immediately cease to exist as individuals.
The following is a list of individual thinkers, philosophers, writers, artists and so on whose works express a notable degree of nondualism. Not all individuals in this list self identify as presenting nonduality. They come from different religious, political and cultural traditions.