An observable feature of learner language, linguistic variability, is described and used as the basis for speculating about an aspect of the process of second language learning. It is hypothesized that variation in correct use of target language forms varies as a function of the demands placed on the learner to produce these forms. Three groups of adult subjects enrolled in community college programs participated in the study. Twenty-six were intermediate English as a second language (ESL) students, 21 were advanced ESL students, and 16 were native speakers of English. Transcripts of planned discussions provided the data of the analysis which examined the use of the Wh-question system and the verb system. The linguistic variability in the data seemed to be systematic. With regard to dimensions of language proficiency, these appeared to be the extent to which the learner's knowledge of the language is analyzed, and the extent to which the knowledge is automatically accessible. The framework generated by these two dimensions describes the learner's knowledge of the language; it serves to separate formal knowledge from the ability to apply known aspects of the language to various purposes. The model derived from the data is that the process of language learning involves the gradual analysis of the structure of language and the development of more fluent retrieval procedures. (AMH)