Epistemic conflicts and the form of epistemic rules

While such epistemic rules as 'If you perceive that X, you ought to believe that X' and 'If you have outstanding testimony that X, you ought to believe that X' seem to be getting at important truths, it is easy to think of cases in which they come into conflict. To avoid classifying such cases as dilemmas, one can hold either that epistemic rules have built-in unless-clauses listing the circumstances under which they don't apply, or, alternatively, that epistemic rules are contributory. This paper explores both responses from a formal perspective, drawing on a simple defeasible logic framework.