The Sarvāstivāda was one of the major Buddhist philosophical schools in India, and they were so named because of their belief that dharmas exist in all three times: past, present and future. Though the Sarvāstivāda Abhidharma system began as a mere categorization of mental events, their philosophers and exegetes such as Dharmatrata and Katyāyāniputra (the compiler of the Mahavibhasa, a central text of the school) eventually refined this system into a robust realism, which also included a type of essentialism. This realism was based on a quality of dharmas, which was called svabhava or 'intrinsic existence'. Svabhava is a sort of essence, though it is not a completely independent essence, since all dharmas were said to be causally dependent. The Sarvāstivāda system extended this realism across time, effectively positing a type of eternalism with regards to time; hence, the name of their school means "the view that everything exists".