This article attempts to highlight the importance of theoretical linguistics and empirical cognitive linguistics studies for the practical teaching of Spanish as a second language. Looking at the domain of subject pronominal use as an example, I endeavor to show how formal linguistics can be useful to language instructors. This is a significant enterprise since language instructors could benefit from both a better understanding of the linguistic properties of the languages they teach and what psycholinguistic studies have revealed about the nature of adult language learning in general. (Contains 1 figure and 7 notes.)