English relative clauses are treated as difficult among Korean EFL learners due to crosslinguistic differences between the two languages. Such crosslinguistic differences are the position of relative clauses, relative pronoun fronting, the existence of a relative pronoun, the morphological form of the relative pronoun, and so on. Evidently, they are important factors that cause the learners a variety of difficulties in their perception of the constructions. In addition to these crosslinguistic differences, I observe that the inability to discern between a relative pronoun and an interrogative pronoun constitutes another major factor that adds to such difficulties. I argue that this results from the lack of knowledge on syntactic and semantic subcategorization and markedness. I accordingly suggest that we should introduce such notions to our formal, explicit, and pedagogical school grammar instruction to enrich the learners’ understanding of English relative clause constructions. (Chungbuk National University)