A Problem for the Closure Argument

Contemporary discussions of skepticism often frame the skeptic's argument around an instance of the closure principle. Roughly, the closure principle states that if a subject knows p, and knows that p entails q, then the subject knows q. The main contention of this paper is that the closure argument for skepticism is defective. We explore several possible classifications of the defect. The closure argument might plausibly be classified as begging the question, as exhibiting transmission failure, or as structurally inefficient. Interestingly, perhaps, each of these has been proposed as the correct classification of Moore's proof of an external world.