Despite the potential benefits of interdisciplinary research (Giacalone Ramat 1995; Preston 1989), there are relatively few recent examples of studies that cross boundaries in an effort to strengthen the individual investigation. The purpose of the current research is to illustrate the importance of applying findings from sociolinguistic research to the investigation of the second-language acquisition (SLA) of copula choice in Spanish by English speakers. Thus, this project supports interdisciplinary approaches to linguistics while at the same time strengthening linguistic knowledge of a particular issue in SLA. Specifically, the current investigation makes use of the application of the semantic transparency variable, shown to be essential in describing language change in progress (Gutierrez 1992a; Silva-Corvalan 1994), to SLA data, which is generally addressed only in terms of the accuracy of learner choice (Ryan and Lafford 1992; VanPatten 1987). The discussion begins with a description of the research context and a justification for the application of semantic transparency to SLA. Finally, original data collected from 72 second-language speakers of Spanish are analyzed in terms of this variable. Evidence is found for the significance of semantic transparency and new ways to categorize learner data and track acquisition are suggested.