Lewis on the Construction of Worlds: the Metaphysical, Epistemic and Practical Costs of Modal Realism

Abstract

This thesis considers the metaphysics and logic of modalities. In the first section, I give a background to modal realism and present Lewis’ motivations for proposing such a view. In the second section, I explain what it means for a theory of modality to be ‘successfully reductive’, why a reduction of modality is important and why Lewis’ view is considered successfully reductive. In the third section, I explain Lewis’ commitments regarding trans-world individuals. In the fourth section, I explain Lewis’ views on impossibility. The final sections will be dedicated to clarifying Lewis’ metaphysical commitments towards the largest domain of possibility and working out their metaphysical, ontological and practical implications. To be clear, this thesis is not intended as a refutation of modal realism. Such a refutation is impossible. Lewis defends modal realism on the grounds of a cost benefit analysis. He believes that the benefits that come with accepting modal realism are enough to justify one’s belief in it. An empirical refutation is impossible because there is no way to verify or falsify the existence of Lewis’ plurality. Every possible world is spatiotemporally isolated from the actual world. Instead of attempting to refute modal realism, this thesis is intended to clarify the fundamental metaphysics of modal realism for the purpose of highlighting the fact that some metaphysical, epistemological and practical costs come with embracing modal realism. The costs I outline are aspects of modal realism that ought to be considered before embracing modal realism.