Dharmadhatu

Historical origin

Kang-nam Oh traces the origin of dharmadhatu to the Avatamsaka Sutra. It has been further developed by the Hua-yen school:

This idea of dharmadhatu-pratītyasamutpāda which was originally found in the Avataṁsaka-sūtra or Hua-yen ching, was fully developed by the Hua-yen school into a systematic doctrine palatable to the Chinese intellectual taste. The dharmadhatu doctrine can be said to have been, by and large, set forth by Tu-shun (557~640 C.E.), formulated by Chih-yen (602~668), systematized by Fa-tsang (643~712), and elucidated by Ch’eng-kuan (ca. 737~838) and Tsung-mi (780~841).

Understanding in Buddhist tradition

Indian Buddhism

Śrīmālādevī Sūtra

The Śrīmālādevī Sūtra (3rd century CE), also named The Lion's Roar of Queen Srimala, centers on the teaching of the tathagatagarbha as "ultimate soteriological principle". It states that the tathagata-garbha is the "embryo" of the Dharmadhatu and the Dharmakaya:

Lord, the Tathagatagarbha is neither self nor sentient being, nor soul, nor personality. The Tathagatagarbha is not the domain of beings who fall into the belief in a real personality, who adhere to wayward views, whose thoughts are distracted by voidness. Lord, this Tathagatagarbha is the embryo of the Illustrious Dharmadhatu, the embryo of the Dharmakaya, the embryo of the supramundane dharma, the embryo of the intrinsically pure dharma.

In the Śrīmālādevī Sūtra, there are two possible states for the Tathagatagarbha:

[E]ither covered by defilements, when it is called only "embryo of the Tathagata"; or free from defilements, when the "embryo of the Tathagata" is no more the "embryo" (potentiality) but the Tathāgata (=the Dharmakaya)(actuality).

The sutra itself states it this way:

This Dharmakaya of the Tathagata when not free from the store of defilement is referred to as the Tathagatagarbha.

Dharmadhātustava

The Dharmadhātustava ("In praise of the Dharmadhatu"), attributed to Nāgārjuna though questioned, is a treatise on the dharmadhatu. According to the Dharmadhātustava, the dharmadhatu is the ground which makes liberation possible:

The dharmadhatu is the ground
For buddhahood, nirvana, purity, and permanence.

According to the Dharmadhātustava, the dharmadhatu is seen when the afflictions are purified:

As butter, though inherent in the milk,
Is mixed with it and hence does not appear,
Just so the dharmadhatu is not seen
As long as it is mixed together with afflictions.

And just as the inherent butter essence
When the milk is purified is no more disguised,
When afflictions have been completely purified,
The dharmadhatu will be without any stain at all.

Chinese Buddhism

Mahaparinirvana Sutra

In the Mahayana Mahaparinirvana Sutra, the Buddha states of himself that he is the "boundless Dharmadhatu" - the totality itself.

Tibetan Buddhism

Five Wisdoms

The Dharmadhatu is comprehended by one of the Five Wisdoms:

1. Dharmadhatu wisdom,
2. Mirror-like wisdom,
3. Equality wisdom,
4. Discriminating wisdom,
5. All-accomplishing wisdom.

Dzogchen

In the Dzogchen text Gold refined from ore, the term Dharmadhatu is translated as "total field of events and meanings" or "field of all events and meanings".