The context of Popper's advocacy of critical rationalism is his defense of the open society. Popper rejects uncritical or comprehensive rationalism as self-defeating and thus an invitation to irrationalism which, in turn, endangers the open society. Bartley argued that a thoroughly critical rationalism can remain comprehensive and consistent, rendering unnecessary Popper's "minimal concession to irrationalism." Popper's rejection of Bartley's claim and the ensuing debate are abstracted from the metapolitical question of the best defense of a rationalism supportive of an open society. This essay surveys the debate over the limits of critical rationalism in terms of Popper's original political, or metapolitical project.