One of the main questions about knowledge is the relation of knowledge to reality. This question is particularly important for the heuristic view of philosophy, according to which philosophy aims at knowledge and methods to acquire knowledge. In the course of the history of philosophy, the question of the relation of knowledge to reality has received several answers. In this chapter, a number of them are briefly discussed and found wanting: direct realism, representative realism, scientific realism, liberalized scientific realism, mathematical structural realism, semantic structural realism, essentialist realism, subjective idealism, and phenomenalism.