Summary.Conversational theory is an attempt to investigate the learning of realistically complex subject matter under controlled conditions. To do this it is necessary to insist on restricted definitions of common terms such as understanding and to demand more stringent conditions before accepting that it has been demonstrated. These conditions can be achieved if the subject matter is structured and the student follows certain rules in demonstrating understanding. Computer linked systems have been developed which control and record student learning. The systems provide the experimenter with detailed records of the learning strategies used by students and the student with learning experiences which normally ensure understanding.