AbstractTo undermine much of what we ordinarily claim to know, sceptics have often appealed to a principle (known as the principle of closure) according to which knowledge (justification) is closed under known entailment. In this paper after expounding the views of Stein, Klein and others, I shall argue that they all fail to take note of different contexts in which the principle of closure is applied. The relevance of the principle of closure for scepticism is then analyzed in the light of, what I call, the ‘infectious’ character of epistemic contexts. I shall also highlight the similarities in the behaviour of the concepts of justification and confirmation and appeal to certain solutions to the paradoxes of confirmation to provide a comprehensive account of the different instances of the principle of clos