This paper argues that crossing the boundaries between sociolinguistics and second language acquisition (SLA) is essential to both fields of study (Giacalone Ramat, 1995; Preston, 1993). Specifically, data collected in an investigation of the SLA of copula choice by 77 English-speaking learners of Spanish are examined in terms of similarities to data collected in studies of language change (Gutiérrez, 1992; Silva-Corvalán, 1994). The variables used to analyze these data, Frame of Reference and Susceptibility to Change, have been shown to be useful for examining the process of the extension of estar to new [copula + adjective] contexts from a sociolinguistic perspective. The application of these variables to SLA data allows an investigation of the mirror-image relationship predicted to exist between the process of language loss and the process of language acquisition.