Linguistic inputs must be syntactically parsable to fully engage the language network.

Whether language comprehension relies predominantly on structural (syntactic) cues or meaning- related (semantic) cues remains debated. We shed new light on this question by examining the language brain areas' responses to stimuli where syntactic and semantic cues are pitted against each other, using fMRI. We find that the language areas respond weakly to stimuli that allow for local semantic composition but cannot be parsed syntactically-as confirmed in a novel behavioral paradigm-and they respond strongly to grammatical but semantically implausible sentences, like the famous 'Colorless green ideas sleep furiously' sentence. These findings challenge accounts of language processing that suggest that syntactic parsing can be foregone in favor of shallow semantic processing.