Essays on the Explanatory Foundation of Vagueness

Vagueness is the phenomenon of borderline cases. Some piles of sand are borderline heaps. Some actions are borderline wrong. My dissertation focuses on the following question: if something is a borderline case, what explains this fact? Linguistic theories of vagueness tell us that all borderline cases are explained by facts involving the semantic unsettledness of the expressions we use to describe them. Metaphysical theories of vagueness tell us that at least some borderline cases are explained (if at all) by the (non-linguistic, non-epistemic) world itself. In the last century of scholarship on vagueness, linguistic theories have emerged as philosophical orthodoxy, while metaphysical theories represent a fringe position. The goal of this project is to motivate the opposite way of looking at things.

Chapter 1 develops and defends an argument originally due to Nathan Salmon against an influential linguistic theory of vagueness: the semantic indecision theory. The argument purports to show that that the semantic indecision theorist has no adequate way to explain the notion of having multiple candidate semantic values, or “precisifications”. Possible responses are considered and rejected.

Chapter 2 develops a related argument intended to bring out why higher order vagueness is a problem for the semantic indecision theorist. I argue that higher order vagueness frustrates the goal of explanation of borderline cases. This is apparent when we consider possible cases involving infinitely many higher orders of vagueness.

Chapter 3 argues that linguistic theories of vagueness are inadequate to explain cases of moral vagueness, if moral realism is true. Assuming the referents of our moral expressions depend upon linguistic behavior, linguistic theories imply that some moral facts depend upon linguistic behavior, contrary to moral realism. I explore whether conceptual role semantics reconciles linguistic theories with moral realism, but find this maneuver unsuccessful.

Chapter 4 explores what theory of metaphysical vagueness we should accept. I evaluate views according to which metaphysical vagueness is a form of restricted possibility. I find that this proposal fails to account for certain phenomena of metaphysical vagueness, which I call “comparable” borderline cases and “necessary” borderline cases. I suggest that theories according to which property instantiation comes in degrees are well-suited to provide an account of such phenomena. Possible replies are considered and rejected.