Characterize the nature of possible worlds (modal realities)

Determine what a possible world (i.e., a maximally specific way reality could be) is, by providing a precise, defensible account of possibilities that can underwrite the modal semantics and analyses used throughout logic and philosophy while remaining consistent with scientific practice.

Background

Chapter 3 surveys the philosophical utility of possible worlds for semantics, counterfactuals, laws, supervenience, and determinism, then turns to the ontological question of what these worlds are. Multiple proposals (e.g., acts of imagination, combinatorial accounts, linguistic/set-theoretic ersatzism, Lewis’s modal realism) are examined with detailed objections, yet none is endorsed.

The author emphasizes that although possible worlds provide substantial explanatory benefits across philosophy and science, their ontological status is unresolved and constitutes a central, difficult issue in modal metaphysics.