The Tathāgatagarbha doctrine is an important teaching in Mahayana and Tantric Buddhism, which affirms that each sentient being contains the intrinsic, effulgent Buddhic element or indwelling potency for becoming a Buddha. "Tathagata-garbha" means "Buddha Womb /Buddha Matrix" or "Buddha Embryo," and this notion is explained by the Buddha in the "Mahayana Mahaparinirvana Sutra" to refer to the "True Self" or "Essence of the Self" within all sentient beings—the unconditioned, boundless, nurturing, sustaining, deathless and diamond-like Self of the Buddha, which is indiscernible to worldly, unawakened vision, as a result of conceptual obscurations, inappropriate mental and behavioural tendencies and unclear perception.
The Tathagatagarbha doctrine is significant because it reiterates the Buddha's affirmation that all beings can attain Buddhahood and become Enlightened because this suchness is already inside of them.
The Sanskrit term "tathāgatagarbha" may be parsed into "tathāgata" and "garba". where the latter has the semantic field: "embryo," "essence"; whilst the former may be parsed into "tathā" (semantic field: "[s]he who has there") and "āgata" (semantic field: "come," "arrived," "not-gone" ) and/or "gata" (semantic field: "gone").
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, as all persons and creatures are compassionately viewed as possessing one and the same essential nature - the Buddha-dhatu or Buddha-nature.
Doctrine of Tathāgatagarbha
The Tathagatagarbha Sutra presents the Tathagatagarbha as a virtual Buddha-homunculus, a fully wisdom-endowed Buddha, inviolate, seated majestically in the lotus posture within the body of each being, clearly visible only to a perfect Buddha with his supernatural vision. This is the most "personalist" depiction of the Tathagatagarbha encountered in any of the chief Tathagatagarbha sutras and is reminiscent of Mahayana descriptions of the Buddha himself sitting in the lotus posture within his own mother's womb prior to birth. Thus, the Tathagatagarbha is only an "embryo" in the sense that it is hidden from worldly view, at the very center of each being, while yet being perfect, unchanging and complete.
Other Tathagatagarbha sutras (notably the Mahaparinirvana Sutra) view the Buddha-garbha in a more abstract, less explicitly personalist manner. However, all agreed that the Tathagatagarbha is an immortal, inherent transcendental Essence 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.
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.
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.
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.
A seminal text associated with this doctrine is the Tathagatagarbha Sutra, which contains a series of very striking, concrete images for what the Tathagatagarbha is, The Lion's Roar Discourse of Queen Srimala (Srimala Sutra), which states that this doctrine is ultimate (not provisional or "tactical"), and perhaps most importantly the Mahayana Mahaparinirvana Sutra, which likewise insists that the tathagatagarbha teaching is "uttarottara"—absolutely supreme—the "final culmination" and "all-fulfilling conclusion" of the entirety of Mahayana Dharma.
Additionally, the Lankavatara Sutra presents the tathagatagarbha as being a teaching completely consistent with and identical to emptiness and synthesizes tathagatagarbha with the sunyata of the prajnaparamita sutras. According to the internal ranking of the sutras, however, the definitive statement on the Tathagatagarbha is to be found not in the Lankavatara Sutra, but in the Mahaparinirvana Sutra, as this is stated by the Buddha (on his "deathbed") therein to be the very final and ultimate explication of true meaning of the doctrine, including in relation to Emptiness.
Tathagatagarbha in Zen
The role of the tathagatagarbha in Zen can not be discussed or understood without an understanding of how tathagatagarbha is taught in the Lankavatara Sutra. It is through the Lankavatara Sutra that the tathagatagarbha has been part of Zen (i.e., Chan) teaching since its beginning in China. Bodhidharma, the traditional founder of Chan-Zen in China, was known for carrying the Lankavatara Sutra with him when he came from India to China. The early Zen/Chan teachers in the lineage of Bodhidharma's school were known as the "Lankavatara Masters." The Lankavatara Sutra presents the Chan/Zen Buddhist view of the tathagatagarbha:
[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.
As a result 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.
The Lankavatara Sutra also states that the tathagatagarba is identical to the alayavijnana known prior to awakening as the storehouse-consciousness or 8th consciousness. Chan/Zen masters from Huineng in seventh-century China to Hakuin in eighteenth-century Japan to Hsu Yun in twentieth-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).
Buddha-nature (Awakened-nature) has been connected in recent decades with the developments of robotics and the possible eventual creation of artificial intelligence. In the 1970s, the Japanese roboticist Masahiro Mori popularized the idea that robots, under certain conditions, may possess Buddha-nature. Mori has since founded an institute to study the metaphysical implications of such technology.
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?