Epistemological questions are often influential in calling our attention to metaphysical issues. For example, we are moved to ask what makes an action morally wrong by questions about how we know of an action that it is morally wrong. (I realize that according to the traditional way of classifying philosophical issues, the question of what makes an action morally wrong is a question of ethics, not of metaphysics. But it is, in the relevant sense, a metaphysical issue in ethics.) In much the same way, we are pushed to ask about the nature of mentality and consciousness by questions about how we know facts about other minds. The problem of laws encounters similar epistemological influences. Many are led to investigate what makes a proposition a law by questioning how we know of a proposition that it is a law. Sometimes the epistemological motivation is slightly less direct, coming from questions regarding our knowledge of causation, the counterfactual conditional, or one of the other nomic concepts.

This interplay between epistemological and metaphysical questions encourages epistemologically oriented metaphysical viewpoints. Berkeley's idealism is a well-known example. Faced with Descartes's epistemological questions, Berkeley advanced a metaphysical position giving us easy access to the external world. Our perceptions, apparently, constitute the basis of our knowledge of the external world; Berkeley's metaphysics has it that our perceptions (along with God's) are what make it the case that facts about the external world obtain.