A glass couldn’t contain water unless it contained H2O-molecules. Likewise, a man couldn’t be a bachelor unless he was unmarried. Now, the latter is what we would call a conceptual or analytical truth. It’s also what we would call a priori. But it’s hardly a conceptual or analytical truth that if a glass contains water, then it contains H2O-molecules. Neither is it a priori. The fact that water is composed of H2O-molecules was an empirical discovery made in the eighteenth century. The fact that all bachelors are unmarried was not. But neither is a logical truth, so how do we explain the difference? Twodimensional semantics is a framework that promises to shed light on these issues. The main purpose of this thesis is to understand and evaluate this framework in relation to various alternatives, to see whether some version of it can be defended.