A priori entailment and the metaphysics of science

Abstract

In this dissertation I develop a framework for evaluating theories of fundamental reality and a related framework for evaluating reductive explanations. The former is the A Priori Entailment thesis (AET), which states that all truths are a priori deducible from the fundamental truths. The latter is the Reduction Entailment thesis (RET), which states that a successful and complete reductive explanation requires that the explanandum is a priori deducible from the explanans. After defending AET/RET I use them to resolve disputes in quantum metaphysics. The dissertation is split into four chapters. The first chapter evaluating the A Priori Entailment Thesis motivates underlying semantic and epistemological theses. It then defines a procedure for evaluating AET: a priori entailment expansions. These formulate problem cases into complex conditionals (of the form 'If [fundamental truths] then [non-fundamental truths]') and breaks them down into a number of simpler conditionals whose epistemic statuses are easier to evaluate. A priori entailment expansions are structured to guarantee that if the expansion conditionals are a priori then the expanded conditional is too. Chapter two A Priori Entailment as a Constraint on Classical Physical Theories constructs a number of entailment expansions showing that AET is true of worlds described by classical physics. Each expansion conditional in each entailment expansion is a case study in itself, with the potential to support or undermine AET. The primary case study shows that mass additivity is an a priori consequence of Newton's fundamental laws. I go on to argue that a particular metaphysical thesis explains these results. This metaphysical thesis strongly suggests that AET holds for any adequate fundamental theory, so AET must be true of the actual world. Chapter three Evaluating the Reduction Entailment Thesis defends RET. I compare the mass additivity expansion to the scientific explanation of mass additivity in physics. I show that the expansion can be seen as the result of removing subtle simplification-induced explanatory gaps exhibited by the scientific explanation. I use this to argue that a priori entailment is necessary for reductive explanation, as it is necessary for the explanatory gaps to be innocuous. I develop a method for systematically converting any reductive explanation into an a priori entailment expansion. I extend the account to inhomogeneous reductive explanations. I then relate RET to the reduction of consciousness and the mind-body problem. The final chapter A Priori Entailment as a Constraint on Quantum Theories assumes AET/RET and is the first detailed attempt at apply AET/RET to solutions to the quantum measurement problem. Such solutions are criticised for failing to reductively explain the manifest world. I evaluate such claims in the context of dynamical collapse theories. I object to the idea that such theories cannot explain why the manifest world appears three-dimensional. However, I provide new reasons for thinking that such theories cannot explain the existence of ordinary objects. In particular, I use AET/RET to show that dynamical collapse theories are empirically false. Show more