This thesis is about modals: words like ‘possible’ and ‘necessary’, ‘must’ and ‘can’. More specifically, it is about their roles in our lives. More specifically still, I want to approach, via the issue of modal function, the relationship between what I call ordinary and philosophical modalizing: the modalizing that we learn in the wild, and the modalizing that we learn in the philosophy classroom. What are the commonalities between these activities? What are their differences?
In order to focus and dramatize the issue, I begin by introducing a figure whom I call the Ascetic Modalizer. The Ascetic Modalizer insists against there being theoretically significant continuities between the modals that we ordinarily use to talk about powers and dispositions, and the modals that some philosophers have called absolute. After arguing that modal semantics, metaphysics, and epistemology may prove too slow a route towards progress in this debate, I suggest that we approach the matter via the neglected topic of modal function.
To get clear on modal function, however, one must first get clear on conditionals. I therefore argue for some novel assertability conditions for subjunctive conditionals, which are informed by the functions of these important constructions. In the process, I shed some light on the differences between kinds of supposition. This discussion of conditionals and suppositions then allows me to draw together two different research programmes in the theory of modal function.
With those resources in hand, I investigate the roles of some ordinary and philosophical modals in our practical and theoretical deliberations. I argue that in so far as those functions are concerned, the Ascetic Modalizer may be right to be sceptical of modal unification. Finally, I show how the preceding discussion intersects with two ancient ideas about modality: that deductive validity requires necessary truth-preservation, and that necessity implies actuality.
