This was one of three AIJ papers that started the field of qualitative reasoning, but I regard it as being superceded by the 1986 paper and my 1994 book. (B.Kuipers)
This paper presents a qualitative-reasoning method for predicting the behavior of mechanisms chracterized by continuous, time-varying parameters. The structure of a mechanism is described in terms of a set of parameters and the constraints that hold among them: essentially a `qualitative differential equation'. The qualitative-behavior description consists of a discrete set of time-points, at which the values of the parameters are described in terms of ordinal relations and directions of change. The behvaioral description, or envisionment, is derived by two sets of rules: propagation rules which elaborate the description of the current time-point, and prediction rules which determine what is known about the next qualitatively distinct state of the mechanism. A detailed example shows how the envisionment method can detect a previously unsuspected landmark point at which the system is in stable equilibrium.