Mathematical and moral disagreement Silvia Jonas August 16, 2019 Abstract The existence of fundamental moral disagreements is a central problem for moral realism and has often been contrasted with an alleged absence of disagreement in mathematics. However, mathematicians do in fact disagree on fundamental questions, for example on which set-theoretic axioms are true, and some philosophers have argued that this increases the plausibility of moral vis-`a-vis mathematical realism. I argue that the analogy between mathemat- ical and moral disagreement is not as straightforward as those arguments present it. In particular, I argue that pluralist accounts of mathematics ren- der fundamental mathematical disagreements compatible with mathematical realism in a way in which moral disagreements and moral realism are not. 1 Keywords: disagreement; mathematical realism; moral realism; set-theoretic pluralism; multiverse; Continuum Hypothesis. 1 Many thanks to Marianna Antonutti, Carolin Antos-Kuby, Claire Benn, Sharon Berry, Chris- tine Bratu, James Brown, Thomas Buchheim, Mark Colyvan, Benedict Eastaugh, Gerhard Ernst, Peter Gerdes, Stephan Hartmann, Jan-Christoph Heilinger, Vera Hoffmann-Kolss, Jessica Isserow, Leora Katz, Christian Kietzmann, Sebastian K¨ ohler, Nicholas Laskowski, Hannes Leitgeb, Toby Meadows, Mark Douglas Warren, Thomas Schmidt, Olla Solomyak, Georgie Statham, Casper Storm Hansen, Marta Sznajder, Christine Tiefensee, Teemu Toppinen, Peter Van Inwagen, Her- man Veluwenkamp, Hugh Woodin, Hannes Wortmann, and three anonymous referees for many helpful comments and discussions. Work on this research paper has been supported by the Min- erva Foundation and the Max Planck Society. 1