Graduate students taking a course in synthetic organic chemistry were asked to think aloud while solving several synthesis tasks. Analysis of the protocols indicated that subjects used different types of representations while problem solving. Subjects constructed solutions and communicated them through seven systems: Verbal, Pictorial, Methodological, Principles-Oriented, Literary, Laboratory-Oriented, and Economic. Beyond the Pictorial and Verbal systems, the most often used system was Methodological in nature—subjects believed the purpose of organic synthesis is to apply rules in a proper order until the task is solved. Subjects considered utilizing other systems of representation if they judged their results to be ambiguous when based on the Methodological system.