In Theravada doctrine, a person may awaken from the "sleep of ignorance" by directly realizing the true nature of reality; such people are called arahants and occasionally buddhas. After numerous lifetimes of spiritual striving, they have reached the end of the cycle of rebirth, no longer reincarnating as human, animal, ghost, or other being. The commentaries to the Pali Canon classify these awakened beings into three types: