The Principle of Sufficient Reason (PSR) says that all contingent facts must have explanation. In this volume, the first on the topic in the English language in nearly half a century, Alexander Pruss examines the substantive philosophical issues raised by the Principle Reason. Discussing various forms of the PSR and selected historical episodes, from Parmenides, Leibnez, and Hume, Pruss defends the claim that every true contingent proposition must have an explanation against major objections, including Hume’s imaginability argument and Peter van Inwagen’s argument that the PSR entails modal fatalism. Pruss also provides a number of positive arguments for the PSR, based on considerations as different as the metaphysics of existence, counterfactuals and modality, negative explanations, and the everyday applicability of the PSR. Moreover, Pruss shows how the PSR would advance the discussion in a number of disparate fields, including meta-ethics and the philosophy of mathematics.

Table of Contents

• • 1 Introduction
  • 2. Reflection on some historical episodes
  • 3. The CP and the PSR; objections to the PSR;
  • 4. A modern version of the Hume objection;
  • 5. The anti-theological argument ‘There are no necessary beings’
  • 6. Modal fatalism
  • 7. Free will
  • 8. Quantum mechanics
  • 9. Turning Leibniz against the PSR
  • 10. What survives the criticisms of the PSR? justification of the PSR
  • 11. Self-evidence
  • 12. Three Thomistic arguments
  • 13. Modal arguments
  • 14. Is the universe reasonable?
  • 15. Explanation of negative states of affairs
  • 16. The puzzle of the everyday applicability of the PSR
  • 17. Inference to the best or only explanation
  • 18. Inductive scepticism
  • 19. The nature of possibility
  • 20. Conclusions.