I defend a claim, central to much work in psycholinguistics, that constructing mental representations of syntactic structures is a necessary step in language comprehension. Call such representations “mental phrase markers”. Several theorists in psycholinguistics, AI, and philosophy have cast doubt on the usefulness of positing MPMs. I examine their proposals and argue that they face major empirical and conceptual difficulties. My conclusions tell against the broader skepticism that persists in philosophy—e.g., in the embodied cognition literature —about the usefulness of positing (...) mental representations in psychological models. Using my discussion of sentence parsing as a case study, I propose several conditions on an appropriate appeal to mental representations. Finally, I point out that the familiar arguments from productivity, systematicity, and inferential coherence suffice to establish that MPMs themselves have a c.. (shrink)