This dissertation concerns the nature and rationality of self-fulfilling beliefs: beliefs whose contents will be true just in case you believe them, because you believe them. Examples of this phenomenon span the quotidian - a child's belief that she will be fed may prompt a parent to begin her feeding - to the complex - as in cases, from the psychology of education, in which student performances match the expectations of their instructors. These examples can be difficult to fit into traditional theories of theoretical reasoning, where the role of theoretical reasoning is to get us on to some independent fact of the matter, by following our evidence. Since there is no independent fact of the matter to track when a belief is self-fulfilling, there will be no evidence of that fact for us to follow. But we are not Cartesian egos, apart from the world and observing it. We ourselves are part of the world we are trying to represent, and so, sometimes, what we believe can affect what the objective world is like. We need an account of theoretical reasoning which can accommodate this fact, and explain how we ought to deliberate about those states of affairs effected by our deliberating