Must . . . Stay . . . Strong!∗ Kai von Fintel MIT Anthony S. Gillies Rutgers University This is a postprint of a paper that appeared in Natural Language Semantics: von Fintel, Kai & Anthony S. Gillies. 2010. Must . . . stay . . . strong! Natural Language Semantics 18(4). 351–383. doi:10.1007/s11050-010-9058-2. 1 The Observation, the Mantra, and the Plan Some epistemic modal expressions are stronge