Computer assisted instruction (CAI) can achieve its potential as a tool for individualizing instruction only if the flexible logic and memory capabilities of computers are utilized. An instructional program must be written in such a way that it can handle at least three variables: (a) who is being taught; (b) what is critical; and (c) how the teaching is to be done. The program must also be capable of choosing the most effective mode of instruction in a given instance: problem solving, drill and practice, inquiry, simulation and gaming, or tutorial instruction. Student response data constitute an additional variable. An idiographic model may be a useful approach to considering both the prescriptive and descriptive aspects of programed instruction. Useful techniques for achieving individualization and student participation may be seen in studies involving the use of CAILAN (CAI language) and symbolic logic as the teaching material. A bibliography supplements the text. (JY)