This article analyses two Sicilian modal constructions involving vuliri 'want' + infinitive and aviri a ‘have to’ + infinitive. They are used to express modal values, both non-epistemic and epistemic, and futurity. Based on Langacker's Cognitive Grammar assumptions, we describe the semantic network associated with each modal, as well as their semantic overlap. In addition, we describe how modal values interact with temporal-aspectual inflection. Our analysis shows that the epistemic values of vuliri are quite peripheral, while aviri a shows a high degree of polysemy, both in the non-epistemic and in the more abstract epistemic domain. The non-epistemic-to-epistemic shifts depend on the contextual coordinates: basically, on the actionality of the verb, and on the agentivity of the Trajector, therefore on the feature of Intentionality which has proved to be crucial in the processes here analysed. On the whole, aviri a exhibits a higher degree of grammaticalisation compared to vuliri: while the latter maintains its “verbiness”, the former appears to be a stable means of modal expression interacting with the other contextual coordinates in a rather complex way.