The modal auxiliaries of English, π-operators in Functional Grammar and “grounding”

In this contribution it is argued that in spite of their homogeneousmorphological and syntactic properties, there are compelling reasons to differentiate the central modal auxiliaries of English with respect to grammaticalization. The main differential semantic criterion comes from their contribution as grounding predications, as understood by Cognitive Grammar. The implications of this differentiation will mainly be investigated for their treatment (as p-operators or otherwise) in Functional Grammar, but it will also entail a modified view for their status as grounding predications in Cognitive Grammar (as compared with Langacker’s). Insights from the diachronic development of must are taken to support the position defended here.