Doctrine important for many schools of Mahayana Buddhism. The Buddha Nature or Buddha Principle (Buddha-dhatu) is taught to be a truly real, but internally hidden, eternal potency or immortal element within the purest depths of the mind, present in all sentient beings, for awakening and becoming a Buddha. In some Mahayana sutras it is equated with the eternal Buddhic Self, the Essence (svabhava) or Soul (atman) which is nothing less than the uncreated and deathless Buddha himself. Nagarjuna, the founder of Madhyamaka, presents a view that states that Buddha-nature is Shunyata (empty). The primary sutras on Buddha-nature maintain that what the Buddha-nature is empty of is not its own ever-enduring reality but impermanence, impurity, moral defects, and suffering - in other words, the painful constrictions and imperfections of samsara.