In his innovative and illuminating monograph, “Abhidharma Doctrines and Controversies on Perception”, Ven. Dhammajoti shows that the cornerstone point of controversy between the Buddhist schools of thought of the middle period of Buddhism, the main of them being Sarvāstivāda, Vaibhāṣika, Dārṣṭāntika, Sautrāntika and Yogācāra, was the problem of the ontological status of the cognitive objects, mainly those perceived visually, and the problem of what actually sees and how exactly that cognitive process happens, tightly intertwined with it. Moreover, the very thesis sarvāstivāda („everything exists [in three times]”) of the Sarvāstivādins hinges upon a certain position in that debate.