Tathāgatagarbha refers to the potential to realize the Buddhahood inherent in all sentient beings. As an ontological foundation for Buddhahood, this potential is described in related sutras as the submerged essence of consciousness possessed by all sentient beings. It is sometimes confused with ālāyavijñāna, because both of them, pure and perfect, provide bases for freedom. From the late Wei and Jin dynasties to the Sui and Tang Dynasty, the study of “the dependent origination of tathāgatagarbha” became popular. It suggests that the tathāgatagarbha heart of all sentient beings opens two gates: the gate of tathāta (suchness) and the gate of generation and destruction. The former refers to the noumenon of tranquility, while the latter denotes the appearance caused by the functioning of ālāyavijñāna. This explains the reason why the noumenon of tranquility is capable of arising and being extinguished.

The tathāgatagarbha of all sentient beings gets entangled in afflictions of all kinds, just like the honey on a tree growing among rocks is guarded by a colony of bees. For all sentient beings, I adopt expedient methods to teach the true dharma, to destroy the bees of afflictions, and to uncover their tathāgatagarbha.  (Tathāgatagarbha Sutra)

The nature of Buddhahood is hidden on some occasions and manifested on others. It is hidden in a state of pollution and manifested when the time is ripe. Some hold that the sentient being’s nature is originally polluted and attains purity only after afflictions get eliminated, but this is not true. As is mentioned in The Exegesis of Sutra on the Lion’s Roar of Queen Śrīmālā, the hidden nature is called tathāgatagarbha, while the manifested nature is called dharmakāya (the body of dharma). What is referred to here is the noumenon rather than the function. (Shi Huiyuan: The Treatise on the Awakening of Faith in the Mahayana)