The grammatical category of modality∗

In many languages, the same words are used to express epistemic and root modality. These modals further tend to interact with tense and aspect in systematic ways, based on their interpretation. Is this pattern accidental, or a consequence of grammar or meaning? I address this question by: (i) comparing ‘grammatical’ modals to verbs/adjectives that share meanings with modals, but not the same scope constraints; (ii) examining patterns of grammaticalization from ‘lexical’ to ‘grammatical’ modality; (iii) comparing scope interactions in languages where modals are ’polysemous’ and in those where they are not.