PATN is a design for a machine problem solver which uses an augmented transition network (ATN) to represent planning knowledge. In order to explore PATN's potential as a theory of human problem solving, a linguistic approach to protocol analysis is presented. An interpretation of a protocol is taken to be a parse tree supplemented by semantic and pragmatic annotation attached to various nodes. This paradigm has implications for constructing a cognitive model of the individual and designing computerized tutors.