 In the Mahayana Buddhist traditions, this idea of the constantly fluctuating nature of the universe is extended in various ways. For some, even those momentary events that make up the flow of the world are understood to be empty of inherent existence (the idea of inherent existence is understood differently in different traditions) to the point that what one sees in the enlightenment experience is the ultimate emptiness (sunyata) of all things. In the Yogacara school of Mahayana Buddhism, this is understood as emptiness of external existence; that is, to see things as they are is to see them as all mind-dependent. In the Zen school of Mahayana Buddhism, the enlightenment experience (kensho) reveals that reality contains no distinctions or dualities. Since concepts and language always involve distinctions, which always involve duality, the insight so gained cannot be achieved conceptually or expressed linguistically. In all Mahayana schools, what brings enlightenment is direct realization of sunyata as a basic fact about reality.