This paper discusses the implications of Lucy Suchman's conclusion that a theory of situated action--i.e., the actual sense that specific users make out of specific Xeroxing events--is truer to the lived experience of Xerox users than a cognitive account of the user's plans--e.g., the hierarchy of subprocedures for how Xerox machines should be used. It is argued that this distinction poses a challenge for cognitively based instructional design because it leads to two questions: whether instructional plans should be designed into instructional systems in order to control instructional interactions when the users of such systems learn in a situated-action manner and not in a plan-based manner, and whether any instructional or learning theory should be used to guide the actions of teachers or learners. Suchman's ideas about plans and situated actions, as well as the implications of these ideas for the design and use of instructional systems, are discussed under the following subheadings: plans and instructional systems; the problematic of plans and instructional practice; plans and situated actions; and plans and situated learning. A brief analysis of the work of John Seely Brown, who is a colleague of Suchman at the Xerox Palo Alto (California) Research Center and one of the founders of the field of intelligent tutoring systems, is then presented. The paper concludes with a discussion of Brown's contention that situated learning is a more accurate account of the phenomena of how people actually learn in the presence of intelligent tutoring systems than the cognitive theory of plans. Appended are 10 graphic representations of various topics discussed in the paper, e.g., the cognitivist paradigm, instructional systems, and aspects of cognition. (27 references) (CGD)