Abstract
The doctrine of radical impermanence expresses the temporal dimension of Buddhist metaphysics, especially in the philosophy of Dharmakīrti and his successors. Most straightforwardly, the doctrine says that everything that exists is momentary; we are not impermanent in the sense that we perish eventually, say when our brain ceases functioning, but rather we perish immediately upon conception. The person who begins to write this sentence and the person who completes it are, strictly speaking, different entities. However, there is a devastating problem for the doctrine: How can any momentary entities be causally efficacious, and more particularly, given their extremely meager duration of existence, how might the momentarist explain the phenomena of cooperation among contemporaneous entities to occasion novel entities, such as seeds, soil, water and sunlight giving rise to sprouts? Even more difficult, can the momentarist offer such an explanation that does not undermine his negative claim that non-momentary things cannot exist? Śāntarakṣita and Ratnakīrti offer answers, but they both fail. By meticulously analyzing and evaluating their arguments, I identify the stumbling blocks of their arguments and show what needs to be done to save the doctrine of momentariness.