Nicholas Longenbaugh, Harvard College ‘16


In this paper, I seek to address a confounding issue surrounding the use of the strong epistemic necessity modal must in English. Traditional accounts of the semantics of must hold that a statement of the form must φ is in fact stronger than a statement of the form φ, so that the truth of the first entails the truth of the second. However, the use of must appears to be precluded in situations where the certainty of the proposition is greatest, which seems to conflict with the proposed strength of must. For example, if I am watching the rain fall outside, (1a) is a reasonable statement, whereas (1b) is significantly less acceptable. However, if instead of watching the rain I merely hear it on the roof, both statements are equally admissible.

(1) a. It’s raining outside.
b. It must be raining outside.

I present an account of the semantics of must that attempts to reconcile these two facts. Ultimately, I claim that the use of must is reserved for situations where you can imagine having better evidence in favor of the claim you are making.

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