In response to the inadequacies in the conception and application of speech act, and on the basis of an in-depth investigation into speech act, a fourth sense of speech act prelocution is proposed, the other three being locution, illocution, and perlocution. The prelocutionary act, the expression of the role,and significance of a single speech act in a speech event can organize coherently all the speech acts so as to propel the speech event in the direction of its communicative goal. The conceptualization of prelocution not only can help disentangle the subtle interrelationship among different senses of acts within a speech act and enrich its connotation, but may contribute to the enhancement of the pragmatic explanatory power of speech act theory and the expansion of its application.