The first goal of this thesis is to propose a satisfying philosophical theory on the nature of fiction, which can account for our ordinary way of making the distinction between fictional and nonfictional works. Although it is tempting to understand fiction simply as the opposite of truth or reality, I show that such views are too simplistic. According to my view, the distinction between fiction and nonfiction lies in the way they are created and evaluated. While nonfiction is constrained by fidelity to facts, fiction is constrained by internal coherence. The importance of internal coherence for fictionality can in turn explain some cases of imaginative resistance – cases where we cannot or will not imagine something, even if this thing is only fictional. Finally, I try to defend some methodological constraints for framing the debate about the nature of our affective reactions to fiction.