A new explanation is proposed for a long standing question in psycholinguistics: Why are some reduced relative clauses so difficult to comprehend? It is proposed that the meanings of some verbs like race are incompatible with the meaning of the reduced relative clause and that this incompatibility makes sentences like The horse raced past the barn fell unacceptable. In support of their hypotheses, the authors show that reduced relatives of The horse raced past the barn fell type occur in naturally produced sentences with a near-zero probability, whereas reduced relatives with other verbs occur with a probability of about 1 in 20. The authors also support the hypotheses with a number of psycholinguistic experiments and corpus studies.