金剛經
While the socalled "Southern School" was said to place emphasis on sudden enlightenment, it also marked a shift in doctrinal basis from the "Laṅkāvatāra Sūtra" to the prajnaparamita tradition, especially the "Diamond Sutra". The Laṅkāvatāra Sūtra, which endorses the Buddha-nature, emphasized purity of mind, which can be attained in gradations. The "Diamond Sutra" emphasizes śūnyatā, which "must be realized totally or not at all".