Abstract:

I aim to formulate a reductive theory of metaphysical necessity. On my account, the notion of necessity originates in the ordinary-life practice of counterfactual reasoning in which we represent certain situations to ourselves and consider what would have been true if these situations had obtained. To simplify considerably, to say that a proposition P is necessary, i.e. that P could not have failed to be true, is to say this: P is true and, for any situation whatsoever, if that situation had obtained P would still have been true. I argue that this account affords us a non-circular way of cashing out the intuition that necessity is truth in all possible situations, and that it yields a plausible explanation of why modal concepts are of practical use to us: Counterfactual reasoning is a component of a common reasoning strategy that is useful for a number of purposes (e.g. making decisions, explaining facts), and modal notions facilitate counterfactual reasoning. Moreover, my theory can be extended to cover other kinds of necessity, such as nomic and conceptual necessity.

It is common to account for counterfactuals using the modal notion of a possible world. My analysis of modal concepts in terms of counterfactuals reverses that order of explanation. I attempt to support this approach by arguing that no modal notions are needed in the theory of counterfactuals and by formulating a non-modal account of their truth-conditions on the basis of a large survey of data. The central idea of this theory is that the truth-value of a counterfactual depends crucially on the explanatory relations between the different facts of the actual world. I use this account of counterfactuals to give a partial explanation of why our practice of counterfactual reasoning bestows special modal force precisely on those propositions (mathematical truths, truths about the laws of nature, etc.) that are in the extensions of metaphysical and nomic necessity. My explanation appeals to the special role that these truths play in explaining other truths.