This paper attempts to integrate several different theories of the second language learning process into a general theory of the human learner. The general theory, which we call the cognitive/conative model, has been developed in the field of instructional psychology and educational measurement by Snow (1990) and Mislevy (1993). It recognizes five types of mental construct: conceptual structures, procedural skills, learning strategies, self-regulatory functions, and motivational orientations. Learning in the model is defined as a change in one or more of these constructs, each of which may be characterized by an initial state, a desired end state, and learning-development transitions between the two. The cognitive/conative model effectively explains individual difference among second language learning processes. It also suggests an architectural view of second language proficiency in which advanced learners do not simply have more of what beginners lack but rather the factors underlying the linguistic performance of beginners and advanced learners are different and interact in different ways. language proficiency in which advanced learners do not simply have more of what beginners lack but rather the factors underlying the linguistic performance of beginners and advanced learners are different and interact in different ways.