Was Hugh MacColl a logical pluralist or a logical monist? A case study in the slow emergence of metatheorising

Abstract

In the mid- and late 1900s Bertrand Russell and Hugh MacColl had a non-discussion about implication and existence, as parts of a dispute over the nature of logic. We are tempted to see this debate in terms of logical monist Russell against logical pluralist MacColl, but I argue that this interpretation is inaccurate; each man was a logical monist, but with different allegiances. The transition from monism to pluralism began to occur from the early 1910s onwards, soon after MacColl’s death in 1909; early traces will be found especially in the American philosopher C. I. Lewis, the Dutch mathematician L. E. J. Brouwer, and the Polish logician Jan Łukasiewicz. They form examples of the gradual rise of metalogic.