The 'all-exists' doctrine
A major early school taught that the past and future are just as real as the present moment.
Sarvāstivāda means, literally, "the doctrine that all exists." It was one of the most important early Buddhist schools, especially in northern India and Central Asia, developing from around the 2nd century BCE. Its distinctive and controversial claim concerned time. Most of us assume the present is real while the past is gone and the future not yet here. The Sarvāstivādins disagreed: the basic constituents of reality—called dharmas, the momentary mental and physical factors into which they analyzed all experience—exist across past, present, and future alike.
Why take such a strange-sounding position? Partly to solve real problems in their system. If a past action is wholly gone, how can it still produce a result (its karmic "fruit") much later? And how can you remember or know a past object if it no longer exists in any way? By saying the factors persist through the three times—changing only in which "mode" of activity they exercise—they kept cause-and-effect and memory intelligible.
Critics, including the Theravāda tradition and later thinkers, charged that this quietly undermined impermanence, a core Buddhist teaching that everything conditioned is in constant flux. The debate was sharp enough that other schools defined themselves partly against it. Though Sarvāstivāda no longer survives as a living lineage, its vast analytical literature deeply shaped later Buddhist philosophy across Asia.