Chance events: According to the Cicero these are events which occurred or will occur in ways which are the uncertain-events which may happen, may not happen, or may happen in some or the other way.

Cicero's classification of such events is close to one dictionary de?nition of chance namely, 'the incalculable element in the existence which renders events unpredictable'. But for Leucippus (the circa 450 B.C.) the operation of possibility was associated with some hidden cause and such a view was held broadly in the middle ages where possibility had no place in the universe, rather all events were thought of as predetermined or fixed by God or by extrinsic causes determined by God. But in 20^th century the deterministic view of the universe was overthrown by the successful and flourishing development of quantum mechanics with its central tenet being that it is impossible to predict the exact outcome of an atomic (or the molecular) system and where this uncertainty or doubt is not due to measurement error or experimental clumsiness but is a fundamental feature of the basic physical laws themselves.