Introduction: In Benincà & Poletto (1994) we have presented evidence, drawn from modal auxiliaries of necessity in some Italian varieties, that the loss of forms in a verbal paradigm is connected to the loss of certain semantic properties of the verb. The idea we have put forth is that verbs' syntax and morphology are determined in some of their aspects by their thematic grid. In this paper, we will show that, the loss of a verb’s thematic grid is accompanied by a change in its syntax and morphology. Thus, the diachronic change described in this paper as a process of grammaticalization provides further confirmation for an analysis originally based on synchronic data.