is. He spent his life enlarging that vision, shaping it, materializing it in a sequence of computer programs that exhibited the very intelligence they explained.
In a remarkable talk about his research strategies and history given at Carnegie Mellon University in December 1991, seven months before his death,2 Allen described his career as aimed single-mindedly at understanding the human mind, but he also confessed to four or five substantial diversions from that goal—almost all of which produced major scientific products of their own. These "diversions" included his work with Gordon Bell on computer hardware architectures, the work with Stu Card and Tom Moran on the psychology of human-computer interaction, a major advisory role in the ARPA program of research on speech recognition, and his leadership in establishing computer science at Carnegie Mellon University and in creating the pioneering computer networking of that university's campus.
For the rest, Allen's work aimed steadily, from the autumn of 1955 onward, at using computer simulation as the key research tool for understanding and modeling the human mind. After the first burst of activity, which produced the Logic Theorist, the General Problem Solver, and the NSS chess program, he focused increasingly on identifying and overcoming the limitations and inflexibilities of these models that impeded their extension into a wholly general theory of the mind. His final book, Unified Theories of Cognition (1990), records the vast progress that he and others made over thirty years toward such generality, progress that in the final decade of his life focused on the emerging Soar system that he and his colleagues built.