his research has been in the area of artificial intelligence, with side excursions into philosophy. his ph.d. dissertation was in the area of automated planning. in that work, he coined the term "task network" to refer to hierarchies of abstract and concrete actions and policies. he did seminal work in non-monotonic logic in the early 1980s, and was an advocate for the "logicist" methodology in ai, defined as formalizing knowledge and reasoning in terms of deduction and quasideduction. in 1987 he published a paper criticizing the logicist approach. the critique was based partly on a previous paper (with steve hanks) pointing out a flaw with all known approaches to nonmonotonic temporal reasoning, embodied in what is now called the yale shooting problem.