Mackereth and Avigad forthcoming in Review of Symbolic Logic

Stephen Mackereth and Jeremy Avigad’s paper “Two-sorted Frege Arithmetic is not Conservative” is forthcoming in the Review of Symbolic Logic! The main result is that Richard Kimberly Heck’s theory of Two-sorted Frege Arithmetic (2FA) is not deductively conservative over pure second- or higher-order logic. It follows that Hume’s Principle is not deductively Field-conservative. Preprint available here: