The concept of buddhanature (bussho), as interchangeable with tathagatagarbha (womb or embryo of tathagata; "one who has thus come," an epithet of the Buddha), arose in Mahayana Buddhism after Nagarjuna (second to third century CE) and before Vasubandhu (fourth to fifth century CE). Sutras from this period are considered middle Mahayana sutras. Before the development of the Mahayana, people generally did not believe they could become buddhas, but some Mahayana Buddhists began to teach that any one of us can become a bodhisattva—a buddha-to-be—if we arouse bodhicitta (awakening mind), take bodhisattva vows, receive bodhisattva precepts, and practice the six paramitas (generosity, discipline, patience, exertion, meditation, and wisdom).
However, probably because they observed themselves and the conditions of the samsaric world—in which so many are self-centered, competitive, in conflict, and have hatred for each other—they needed to instill some faith that buddhahood was within reach. Even if the people of the world were deluded, their minds defiled with the three poisons, they could eventually reach buddhahood if they continued to practice the Buddha's teachings.
They developed the concept of buddhanature—that is, the pure undefiled mind as the essential self-nature, hidden and covered as it may be thanks to our deluded, discriminative minds. According to those middle Mahayana sutras, buddhanature is permanent, without change, whether in deluded living beings or in enlightened buddhas. It continues to exist, life after life, until buddhahood is reached, no matter how long it might take. Some people criticized this theory, arguing that buddhanature sounded like atman, the permanent self that Shakyamuni had negated. (Read more here)
