Since its inception in the work on fallacies of Charles Hamblin, formal dialectic has been the object of an unparalleled level of optimism concerning the potential of its analytical contribution to fallacy inquiry. This optimism has taken the form of a rapid proliferation of formal dialectical studies of arguments in general and fallacious arguments in particular under the auspices of theorists such as Jim Mackenzie and John Woods and Douglas Walton, to name but a few. Notwithstanding the interest in, and (...) the hopes for, a formal dialectical analysis of the fallacies, such an analysis, I will demonstrate subsequently, leads to much unintelligibility in fallacy inquiry. The context of my argument will be the philosophical views of Hilary Putnam, particularly Putnam's claim that when we theorise in relation to rationality, the unintelligibility of the conception of rationality to emerge from this theoretical process can be traced to the circumscription of rationality within this theoretical process. I charge formal dialectic with effecting a similar circumscription of argumentative rationality, a circumscription that, I will claim, is generative of unintelligibility in formal dialectical analyses of the fallacies. In this case, the context for my claims will be the formal dialectical analyses of Walton and Batten, Rescher, Hamblin, Mackenzie and Hintikka, primarily in relation to the petitio principii fallacy. My conclusion examines a number of the reasons, both historical and conceptual, which have made it seem that it is possible to fully circumscribe the notion of argumentative rationality. (shrink)