Discussions of "systems" and the "systems approach" tend to fall into one of two categories: the panegyrical and the disparaging. Scholars who praise the systems approach do so in the belief that it is a powerful and precise method of study. Scholars who try to shoot it down fail to see any advantage in it; indeed, many deem it periIicious. Van Dyne (1980, p. 889) records a facetious comment he once heard, the gist of which ran: "In instances where there are from one to two variables in a study you have a science, where there are from four to seven variables you have an art, and where there are more than seven variables you have a system". This tilt at the systems approach is mild indeed compared with the com­ ments of an anonymous reviewer of a paper by myself concerned with the systems approach as applied to the soil. The reviewer stated bluntly that he or she had no time for an approach which falsifies and belittles work that has been done and is of no use for future work. My summary of the paper opened with the seemingly innocuous sentence "The notion of the soil as a system is placed on a . formal footing by couching it in terms of dynamical systems theory".

I Introduction.- 1 Systems and Models.- II Conceptual Models.- 2 Simple and Complex Systems.- 3 Form and Process Systems.- III Mathematical Models.- 4 Deductive Stochastic Models.- 5 Inductive Stochastic Models.- 6 Statistical Models.- 7 Deterministic Models of Water and Solutes.- 8 Deterministic Models of Slopes and Sediments.- 9 Dynamical Systems Models.- 10 Conclusion and Prospect.- References.