The Rules of Thought develops a rationalist theory of mental content while defending a traditional epistemology of philosophy. Jonathan Jenkins Ichikawa and Benjamin W. Jarvis contend that a capacity for pure rational thought is fundamental to mental content itself and underwrites our quotidian reasoning and extraordinary philosophical engagement alike. Part I of the book develops a Fregean theory of mental content, according to which rational relations between propositions play a central role in individuating contents; the theory is designed to be sensitive not only to Frege's puzzle and...