Certainly but not certain: The expression of subjective and objective probability

This paper investigates the interpretation of the epistemic modal adjectives possible, certain and their adverbial counterparts possibly, certainly, taking the perspective that the former express objective modality, whereas the latter express subjective modality. In support of this view, we report on two experiments that assess speakers' acceptance of possible, certain, possibly, certainly in different contexts. Our results extend those of Lassiter (2016) in demonstrating a difference in interpretation between the adjectival and adverbial modals, with possibly less acceptable than possible but conversely certainly more acceptable than certain in the same situations. Furthermore, the results of our experiments suggest a new insight, namely that these differences depend, to some extent, on the probability of the eventuality in question and polarity of the prejacent sentence.