The doubt-whether puzzle

The predicate doubt exhibits a distinctive selectional restriction: it is compatible with declarative and whether-complements but is incompatible with constituent wh-complements. The interpretation of a whether-complement under doubt is also puzzling, as doubt whether p is almost—but not completely—synonymous with doubt that p. This chapter presents a semantic account of these facts, based on the mechanisms of highlighting and exhaustification. Doubt expresses an existential doxastic attitude toward the negation of the highlighted content of the complement while having presuppositions that are sensitive to the ordinary content of the complement. Since that p and whether p are equivalent in the highlighted content but non-equivalent in the ordinary content, the semantics explains fine-grained differences in interpretations between doubt whether p and doubt that p. Furthermore, due to the absence of a stronger scalemate, the interpretation of doubt that/whether p undergoes strengthening via exhaustification, akin to the behavior of scaleless modals.