Semantically, viewpoint aspect encodes boundedness, the specification (or lack thereof) of a temporal boundary. Perfective viewpoint is bounded and situations presented in the perfective have reached the temporal boundary, whereas imperfective viewpoint is unbounded and situations presented in the imperfective have not. This semantic difference is reflected through the imperfective paradox interaction: telic predicates in the imperfective, but not those in the perfective, lose their completion entailments. Pragmatically, viewpoint aspect serves different discourse functions; the imperfective provides background information and it suspends the plot, whereas the perfective provides foreground information and it moves the plot along. This study examines Korean speakers understanding of the aforementioned semantic and pragmatic properties of viewpoint aspect in English. Results showed successful acquisition of the pragmatics but delayed acquisition of the semantics. It is argued that this disparity is accounted for by transfer of partial completion construals of perfectives in Korean. It also addresses implications of the results in light of the Interface Vulnerability Hypothesis arguing for the vulnerability of the syntax-pragmatics interface as compared to the syntax-semantics interface.