In Mahayana and Tantric Buddhism, the Tathāgatagarbha (如來藏) doctrine (often essentially the same as the Buddha nature concept) teaches that each sentient being contains the intrinsic, effulgent Buddhic element or indwelling potency for becoming a Buddha. There are conflicting interpretations of the idea in Mahayana thought. The idea may be traced to Abhidharmic thought, and ultimately to statements of the Buddha in the Nikayas. Buddha-nature and sugatagarbha are synonyms for tathagatagarbha.
Other Tathagatagarbha sutras (notably the Mahaparinirvana Sutra) view the Buddha-garbha in a more abstract, less explicitly personalist manner. But all are agreed that the Tathagatagarbha is an immortal, inherent transcendental essence or potency and that it resides in a concealed state (concealed by mental and behavioural negativities) in every single being (even the worst - the icchantika). The Tathagatagarbha doctrine is also presented as an antidote to a false, nihilistic understanding of Emptiness (Shunyata), wherein even Nirvana and the Buddha are wrongly viewed (according to the doctrine of these scriptures) as illusory and unreal. In the Mahaparinirvana Sutra, the Buddha further explains how he only gives out his secret teachings on the Tathagatagarbha when his disciples are no longer like "small children" of limited capacity and of paltry assimilative power, but have "grown up" and can no longer be satisfied with the simple spiritual food they had initially been fed. While his disciples were still immature, they were only able to "digest" the simple and basic spiritual fare of "suffering, impermanence and non-Self", whereas once they have reached spiritual adulthood they require more spiritual nutriment and are now ready to assimilate the culminational teachings of the Tathagatagarbha.
Although attempts are made in the Buddhist sutras to explain the Tathagatagarbha, it remains ultimately mysterious and allegedly unfathomable to the ordinary, unawakend person, being only fully knowable by perfect Buddhas themselves. As the Srimala Sutra states: "the Tathagatagarbha is the sphere of experience of the Tathagatas [Buddhas] ...". It cannot even be seen clearly by 10th-level (i.e. highest level) Bodhisattvas - although they vaguely perceive its presence. Yet once it is fully "seen and known", on that morning the Bodhisattva "attains the sovereign Self" (aishvarya-atman) and Buddhahood is achieved (The Mahayana Mahaparinirvana Sutra in 12 Volumes, tr. by Kosho Yamamoto, ed. by Dr. Tony Page, Nirvana Publications, London, 2000, Vol. 8, p. 42). The Nirvana Sutra, which presents itself as the final teachings of the Buddha on the Tathagatagarbha, makes clear that there are two kinds of self of which he speaks: one mundane and mutable, the other Buddhic and eternal. The first is denied as truly real, while the second is affirmed as the only true Reality (The Mahaparinirvana Sutra in 12 Volumes, tr. by Kosho Yamamoto, ed. by Dr. Tony Page, Nirvana Publications, London, 2000, Vol. 3, p. 1 and passim). In this same sutra the Buddha explains that he proclaims all beings to have Buddha-nature (which is used synonymously with tathagatagarbha in this sutra) in the sense that they will in the future become Buddhas. In the later Lankavatara Sutra it is said that the tathagatagarbha might be mistaken for a Self, which it is not.
In some sutras the Tathagatagarbha, while being monistic and ineffably non-dual, is also on occasion presented as being possessed of two elements, one essential, immutable, changeless and still, the other active and salvational. As Professor Robert E. Buswell Jr. writes in connection with the Vajrasamadhi-sutra: "This 'dharma of the one mind', which is the 'original tathagatagarbha', is said to be 'calm and motionless' ... The Vajrasamadhi's analysis of tathagatagarbha also recalls a distinction the Awakening of Faith makes between the calm, unchanging essence of the mind and its active, adaptable function ... the tathagatagarbha is equated with the 'original edge of reality' (bhutakoti) that is beyond all distinctions - the equivalent of original enlightenment, or the essence. But tathagatagarbha is also the active functioning of that original enlightenment - 'the inspirational power of that fundamental faculty' .... The tathagatagarbha is thus both the 'original edge of reality' that is beyond cultivation (= essence) as well as the specific types of wisdom and mystical talents that are the byproducts of enlightenment (= function). ...." The Tathagatagarbha itself thus needs no cultivation, only uncovering or dis-covery, as it is already present and perfect within each being.
The Tathagatagarbha doctrine arose with the Mahayanists and later became linked (in a less "pure", more syncretic form - e.g. in the Lankavatara Sutra) with those who were associated to some degree or another with Citta-matra ("just-the-mind") or Yogacara studies, aiming clearly to account for the possibility of the attainment of Buddhahood by ignorant sentient beings (the "Tathagatagarbha" is the indwelling bodhi - Awakening - in the very heart of Samsara). There is also a tendency in the Tathagatagarbha sutras to support vegetarianism (see vegetarianism in Buddhism), as all persons and creatures are compassionately viewed as possessing one and the same essential nature - the Buddha-dhatu or Buddha-nature.
Some of the most important early texts for the introduction and elaboration of the Tathagatagarbha doctrine are the Mahayana Mahaparinirvana Sutra, the Tathagatagarbha Sutra, the Śrīmālā-sūtra, the Anunatva-Apurnatva-Nirdesa sutra, and the Angulimaliya Sutra; the later commentarial/exegetical-style texts, the Awakening of Faith in the Mahayana scripture and the Ratna-gotra-vibhaga summation of the Tathagatagarbha idea had a significant influence on the understanding of "Tathagatagarbha" doctrine.
The concept of the Tathagatagarbha is closely related to that of the Buddha-nature; indeed, in the Angulimaliya Sutra and in the Mahayana Mahaparinirvana Sutra, which latter is the lengthiest sutra dealing with the immanent and transcendent presence of the Tathagatagarbha within all beings, the terms "Buddha-nature" ("Buddha-dhatu") and "Tathagatagarbha" are employed as synonymous concepts.
Belief and faith in the true reality of the Tathagatagarbha is presented by the relevant scriptures as a positive mental act and is strongly urged; indeed, rejection of the Tathagatagarbha is linked with highly adverse karmic consequences. In the Angulimaliya Sutra, for instance, it is stated that teaching only non-Self and dismissing the reality of the Tathagatagarbha, karmically leads one into most unpleasant rebirths, whereas spreading the doctrine of the Tathagatagarbha will bring benefit both to oneself and to the world. We read:
"Those who were donkeys in previous lives and paid no attention to the Tathâgata-garbha are now poor and eat coarse food as donkeys do. In future lives, too, apart from being poor, they will be born into lowly kshatriya [military] families. These are none other than the people who have no faith in the Tathâgata-garbha and cultivate the notion of no-Self, for they will be like prostitutes, outcastes, birds and donkeys ...
"People who lack learning and have wrong views get angry with those who teach the Tathâgata-garbha to the world, and [those unlearned people] expound non-Self in place of the Self as their doctrine. He who teaches the Tathâgata-garbha, even at the expense of his own life, knowing that such people are inexperienced with words and lacking in balance, has true patience and teaches for the benefit of the world."
Caution is required when discussing the doctrine of the Tathagatagarbha (as presented in the primary tathagatagarbha-sutric texts), so that the Tathagatagarbha does not become inaccurately denigrated or reduced to a "mere" tactical device or become dismissed as just a metaphor with no actual ontological reality behind it in the here and now (it is incorrect from the perspective of the Tathagatagarbha sutras to view the Tathagatagarbha solely as some future as yet non-existent potential or as a vacuous Emptiness; the Tathagatagarbha is not constrained by time, not subsumed within the past-present-future confines of temporality, but is changeless and eternal); conversely, it is erroneous to construe the Tathagatagarbha as a tangible, worldly, mutating, passion-dominated, desire-driven "ego" on a grand scale, similar to the "ego-lie" comprised of the five mundane skandhas (impermanent mental and physical constituents of the unawakened being). The Tathagatagarbha is indicated by the relevant sutras to be one with the Buddha, just as the Buddha is the Tathagatagarbha at the core of his being. The Tathagatagarbha is the ultimate, pure, ungraspable, inconceivable, irreducible, unassailable, boundless, true and deathless Quintessence of the Buddha's emancipatory Reality, the very core of his sublime nature (Dharmakaya). The Tathagatagarbha is, according to the final sutric teaching of the Mahayana Nirvana Sutra, the hidden interior Buddhic Self (Atman), untouched by all impurity and grasping ego. Because of its concealment, it is extremely difficult to perceive. Even the "eye of prajna" (insight) is not adequate to the task of truly seeing this Tathagatagarbha (so the Nirvana Sutra): only the "eye of a Buddha" can discern it fully and clearly. For unawakened beings, there remains the springboard of faith in the Tathagatagarbha's mystical and liberative Reality.
[The Buddha said,} Now, Mahāmati, what is perfect knowledge? It is realised when one casts aside the discriminating notions of form, name, reality, and character; it is the inner realisation by noble wisdom. This perfect knowledge, Mahāmati, is the essence of the Tathāgata-garbha.Because of the use of expedient means (upaya) by metaphors (e.g., the hidden jewel) in the way that the tathagatagarbha was taught in some sutras, two fundamentally mistaken notions arose. First that the tathagatagarba was a teaching different from the teaching of emptiness (sunyata) and that it was a teaching that was somehow more definitive than emptiness, and second that tathagatagarbha was believed to be a substance of reality, a creator, or a substitute for the ego-substance or fundamental self (atman) of the Brahmans. Responding to these two mistaken notions, in Section XXVIII of the Lankavatara, Mahamati asks Buddha, "Is not this Tathagata-garbha taught by the Blessed One the same as the ego-substance (atman) taught by the philosophers?"
The Blessed One replied: No, Mahamati, my Tathagata-garbha is not the same as the ego taught by the philosophers; for what the Tathagatas teach is the Tathagata-garbha in the sense, Mahamati, that it is emptiness, reality-limit, Nirvana, being unborn, unqualified, and devoid of will-effort; the reason why the Tathagatas who are Arhats and Fully-Enlightened Ones, teach the doctrine pointing to the Tathagata-garbha is to make the ignorant cast aside their fear when they listen to the teaching of egolessness and to have them realise the state of non-discrimination and imagelessness. I also wish, Mahamati, that the Bodhisattva-Mahasattvas of the present and future would not attach themselves to the idea of an ego [imagining it to be a soul]. Mahamati, it is like a potter who manufactures various vessels out of a mass of clay of one sort by his own manual skill and labour combined with a rod, water, and thread, Mahamati, that the Tathagatas preach the egolessness of things which removes all the traces of discrimination by various skilful means issuing from their transcendental wisdom, that is, sometimes by the doctrine of the Tathagata-garbha, sometimes by that of egolessness, and, like a potter, by means of various terms, expressions, and synonyms. For this reason, Mahamati, the philosophers' doctrine of an ego-substance is not the same as the teaching of the Tathagata-garbha. Thus, Mahamati, the doctrine of the Tathagata-garbha is disclosed in order to awaken the philosophers from their clinging to the idea of the ego, so that those minds that have fallen into the views imagining the non-existent ego as real, and also into the notion that the triple emancipation is final, may rapidly be awakened to the state of supreme enlightenment. Accordingly, Mahamati, the Tathagatas who are Arhats and Fully-Enlightened Ones disclose the doctrine of the Tathagata-garbha which is thus not to be known as identical with the philosopher's notion of an ego-substance. Therefore. Mahamati, in order to abandon the misconception cherished by the philosophers, you must strive after the teaching of egolessness and the Tathagata-garbha.Also as described in the Lankavatara, in Chan/Zen the tathagatagarba is identical to the alayavijnana known prior to awakening as the storehouse-consciousness or 8th consciousness. Chan/Zen masters from Huineng in 7th century China to Hakuin in 18th century Japan to Hsu Yun in 20th century China, have all taught that the process of awakening begins with the light of the mind turning around within the 8th conscousness, so that the alayavijnana, also known as the tathagatagarbha, is transformed into the "Bright Mirror Wisdom". When this active transformation takes place to completion the other seven consciousnesses are also transformed. The 7th conscousness of delusive discrimination becomes transformed into the "Equality Wisdom". The 6th consciousness of thinking sense becomes transformed into the "Profound Observing Wisdom", and the 1st to 5th consciousnessses of the five sensory senses become transformed into the "All-performing Wisdom".
As D.T. Suzuki wrote in his introdution to his translation of the Lankavatara Sutra,
"Let there be, however, an intuitive penetration into the primitive purity (prakritiparisuddhi) of the Tathagata-garbha, and the whole system of the Vijnanas goes through a revolution."This revolution in the system of consciousness (vijnana) is what Chan/Zen calls awakening or "kensho", seeing into one's own nature.
Therefore, in modern-Western manifestations of the Zen Buddhist tradition, it is considered insufficient simply to understand Buddha-nature intellectually. Rather tathagatagarbha must be experienced directly, in one's entire bodymind. Enlightenment in a certain sense consists of a direct experience (gata) of the essence or womb (garbha) of thusness (tatha) and this is the tathagatagarbha of one's own mind, which is traditionally described and designated as śūnyata (emptiness).
The Zen tradition often uses koan to evoke the revolution in consciousness of the turning of the light back to the tathagatagarbha or Buddha-nature. According to one of the most famous koans, a monk once approached the Zen master Chao-chou (Japanese: Jōshū) and asked him, "Does a dog possess Buddha-nature or not?" Chao-chou replied with the one-word answer "Wú" (pronounced "mu" in Japanese), literally meaning "no" or "without." Through an inquiring contemplation of the question and response, one may come to detach from the phenomena of externals in which the six sense conscoiusnesses are usually enthralled and realize the turning around of the light of the mind to gain a direct insight into the tathagatagarba of Buddha-nature.
The implication or the question is, can a perfect simulation of intelligent outward behaviour really light the inner spark of a self-aware consciousness principle in an artificial entity? Given the doctrine of anatman, is there any difference between the subjective experiences of a robot that acts intelligent and an animal that is intelligent?