It is widely held that ordinary natural language conversations are governed by tacit conventions. called felicity conditions or conversational postulates (Austin. 1962: Grice. 1975: Gordon and Lakoff, 1975). Learning a procedural skill is also a communication act. The teacher communicates a procedure to the student over the course of several lessons. The central idea of the theory to be presented is that there are specific felicity conditions that govern learning. In particular, five newly discovered felicity conditions govern the kind of skill acquisition studied here. The theory has been embedded in a learning model. a large Al-based computer program. The model' s performance has been compared to data from several thousand students learning ordinary mathematical procedures: subtracting multidigit numbers, adding fractions, and solving simple algebraic equations. A key criterion for the theory is that the set of procedures that the model learns should exactly match the set of procedures that students actually acquire, including their "buggy" procedures. However, much more is needed for psychological validation of this theory, or any complex Al-based theory, than merely testing its predictions. The method used with this theory is presented.