Acknowledgements; Part I. Mathematical Practice and its Puzzles: 1. Metaphysical inertness; 2. Metaphysical inertness and reference; 3. The virtues of (second-order) theft; 4. Intuitions about reference and axiom systems; 5. Comparing mathematical terms and empirical terms I; 6. Comparing mathematical terms and empirical terms II; 7. The epistemic role puzzle; 8. Benacerraf's puzzle; 9. Comparing puzzles; 10. Quine's approach I; 11. Quine's approach II; Part II. The Stuff of Mathematics: Posits and Algorithms: 12. Introduction; 13. An initial picture; 14. Application and truth; 15. Systems, application and truth; 16. Quine's objections to truth by convention; 17. Grades of ontological commitment; 18. Multiply interpreting systems; 19. Intuitions about reference revisited; Part III. The Geography of the A Priori: 20. Introduction; 21. Algorithms again; 22. Some observations on metamathematics; 23. Incorrigible co-empiricalness; 24. Why there are no incorrigible co-empirical truths; 25. Normative considerations, the success of applied mathematics, concluding thoughts; Appendix; Bibliography; Index.