Controversies invoking the concept of canonicity tend not merely to jump the gun - they assume that there is actually something to debate or discuss, that there are canons or canonical objects which can be deconstructed or preserved, analysed or appreciated. This thesis offers an approach to canonicity which rejects this assumption, but without abandoning the concept. It reconceives the basis of canonicity, through an analysis of the idea of incommensurability and of the hermeneutic or interpretive ideal of openness, by locating the concept and its applications within a semantics of interpretation and recovery which dismisses the very idea of shared structures of canonical meaning. In this way the approach follows Donald Davidson's well-known efforts to avoid a reification of linguistic meaning. The reconception of canonicity offered, however, owes perhaps more to the hermeneutic theories of Hans-Georg Gadamer and to Friedrich Nietzsche's conception of self-transformation. Drawing on all three philosophers it makes canonicity a function of the application of openness within certain kinds of incommensurable discourses, ones which are shaped by and reshape a subject's historical ground; in addition it suggests a resolution to a problem of openness and incommensurability which fundamentally reconceives both concepts.