The idea of the impermanence and transience of life is absolutely fundamental to Buddhist teachings. The first of the Three Characteristics (ti-lakkhana, dukkha, anatt), 'impermanence', is a doctrine constantly and emphatically insisted upon in the canonical texts. The radical and extended interpretation of this doctrine gave rise to the idea that the world is not made of enduring substances with changing qualities. Rather, reality is made only of events that flash into and out of existence, not only through the causal power of their chief cause but also through the influence of an entire causal complex. This is referred to as ksanikav¡da, the doctrine of momentariness.

There is disagreement among Buddhist thinkers about the exact meaning of the doctrine of momentariness. Some thinkers hold that no conditioned phenomenon can endure for more than a single moment, after which it stops existing. Others, though, argue that momentariness is not incompatible with duration; things are produced, endure and disappear. In particular, the Theravadins attempts to model the thought process in terms of the relative duration of material and mental phenomena. In fact, the Theravādin exegetes hold that a moment of matter lasts for as long as sixteen or seventeen thought moments.

The central part of this thesis examines the origin and development of this version of the doctrine of momentariness. There is difficulty in establishing when it appeared. Some scholars think that the Theravādins did not develop the doctrine early on in their history. They believe that it may have been interpolated into Theravādin textual sources at a later date, possibly by Buddhaghosa in the fifth century CE. I take quite a different position. My hypothesis is that the Theravādin doctrine of momentariness was embedded in the early Sinhalese commentaries. To prove it, I have made a close study of the textual evidence. All of it seems to confirm that the doctrine was formed early in the Theravādin tradition and that Buddhaghosa did not introduce the doctrine.

In its attempt to trace the textual history of the Theravādin doctrine of momentariness, this thesis contributes to the study of the early history of Buddhist thought, by examining the parallel textual sources of the early Southern and Northern traditions (between the first century BCE and the second century CE) before they are formalised, in the Visuddhimagga and the Abhidharmako'abh'sya respectively, in the fifth century CE.