The Spread of Grammaticalized Forms The Case of be+supposed to

This research considers the importance of pragmatic motivation in the diffusion of grammaticalized forms, focusing upon the changes in meaning of the construction be+supposed to and the ambiguity that emerges when multiple interpretations become available. The passive form of the main verb to suppose develops into a grammaticalized semimodal construction with deontic and epistemic senses. This work examines the ways that the ambiguity that develops when the pregrammaticalized and the grammaticalized forms coexist can itself propel the change: assisting in the initial spread of the grammaticalized usage and then suppressing the older pregrammaticalized form. Using the British National Corpus, the Chadwyck-Healey Database of Nineteenth-Century Fiction, and the ARCHER corpus, I find that the influences of genre and frequency can create pragmatic conditions which encourage the diffusion of grammaticalized forms between text types.