The "doubt-whether" puzzle

The English predicate doubt is known to exhibit a distinctive selectional restriction: it is compatible with declarative as well as 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⌝. I will argue that these behaviors of doubt can be given a semantic account, by making use of 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. Given that ⌜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, given the lack of a stronger scalemate, the interpretation of ⌜doubt that/whether p⌝ undergoes strengthening due to exhaustification, akin to the behavior of ‘scaleless’ modals reported in the literature.