Rationis Defensor is to be a volume of previously unpublished essays celebrating the life and work of Colin Cheyne. Colin was until recently Head of the Department of Philosophy at the University of Otago, a department that can boast of many famous philosophers among its past and present faculty and which has twice been judged as the strongest research department across all disciplines in governmental research assessments. Colin is the immediate past President of the Australasian Association for Philosophy (New Zealand Division). He is the author of Knowledge, Cause, and Abstract Objects: Causal Objections to Platonism (Springer, 2001) and the editor, with Vladimir Svoboda and Bjorn Jespersen, of Pavel Tichy's Collected Papers in Logic and Philosophy (University of Otago Press, 2005) and, with John Worrall, of Rationality and Reality: Conversations with Alan Musgrave (Springer, 2006). This volume celebrates the dedication to rational enquiry and the philosophical style of Colin Cheyne. It also celebrates the distinctive brand of naturalistic philosophy for which Otago has become known. Contributors to the volume include a wide variety of philosophers, all with a personal connection to Colin, and all of whom are, in their own way, defenders of rationality. ​