A definition is given of expectancy of events projected into the future by a complex temporal sequence. The definition can be decomposed into basic expectancy components projected by each time interval implicit in the sequence. A preliminary formulation of these basic curves is proposed and the (de) composition method is stated in a formalized, mathematical way. The resulting expectancy of complex temporal patterns can be used to model such diverse topics as categorical rhythm perception, clock and meter inducement, rhythmicity, and the similarity of temporal sequences. Besides expectancy projected into the future, the proposed measure can be projected back into the past as well, generating reinforcement of past events by new data. The consistency of the predictions of the theory with some findings in categorical rhythm perception is shown.