The prominence of the concept of utterance has emerged from some recent grammars based on corpora of speech. This paper deals with a new definition of utterance as the realization of an illocutionary value and on the ground of the hypothesis of an existing equivalence between units belonging to the field of human actions (acts) and linguistic units (utterances). Furthermore it is proposed a definition of illocution, which diverges from that of Searle. This kind of definition brings to a new taxonomy of illocution on an attitudinal ground (affect) and on the basis of pragmatic, semiologic and cognitive features. Results of experimental researches on speech corpora are provided: with the recognition of the existing equivalence between utterance and illocution it is possible to verify the concrete variation of acts and to identify intonational contours which are singularly devoted to the expression of illocution. This brings to the formulation of a first repertoire of intonational contours with illocutionary value. Some of these contours, studied on the basis of this theoretical approach, are showed.