Certainty and possibility

This chapter discusses several more epistemic adjectives. Certain and its near-synonym sure are maximum adjectives that combine with proportional and percentage modifiers. A comparison with non-modal adjectives suggests a ratio-scale classification with at least an upper bound. Several lines of evidence indicate that certainty and likelihood are formally closely related. However, there are puzzles around the interpretation of uncertain that indicate that the relation may not be one of identity. I consider three possible analyses, all of which have certain advantages and drawbacks. I then turn to possible, which is often claimed to be non-gradable. Naturalistic data indicate that possibility is a graded concept (e.g., increase the possibility of), and that possible is gradable (e.g., too/very/n% possible). While an analysis in terms of some kind of scalar coercion is technically feasible, the most natural explanation is that possible is a gradable adjective whose scale is closely related to likely’s scale.