This discussion of the utilization by computer designers and users of metaphors as organizing structures for dealing with the complexity of behavior of human/computer interfaces begins by identifying three types of metaphor that describe various aspects of human-computer interface design, i.e., activity, mode of interaction, and task domain. The primary focus of this paper is four metaphors for the mode of interaction: (1) conversation, in which the interface is an implied intermediary between the user and the world in which actions are taken; (2) declarations, which change the world they refer to by changing the agreement under which something does or does not exist; (3) model world, in which expressions in the interface language appear as actions with causal force in the world of interest and the generation of expressions is constrained so that it is not possible to compose an expression that cannot be realized in the world of interest; and (4) collaborative manipulation, in which the conversation and model-world interfaces are combined. The discussion shows how mode of interaction metaphors are essential to the user's interpretation of the behavior of the interface; how interface designers encourage particular metaphorical interpretations of the interfaces they design; and how the choice of metaphor has important consequences for both the designers and the users of interfaces. Seventeen references are provided. (MES)