Modal logics with the Macintosh rule

Conclusion Having gained some idea of what MacIntosh logics there are, we conclude this paper with a remark about the totality of them. Let theterritory of a rule or condition be the class of all modal logics that have the rule or satisfy the condition. What is MacIntosh territory, the class of all normal logics with the MacIntosh rule, like? What is its structure?We are especially indebted to Max Cresswell, Rob Goldblatt, Steve Kuhn, Jack MacIntosh, Tamara Ollenberg, and Tim Williamson for very helpful contributions along the way to the present version of this essay. Elements of it were presented by Chellas at a miniconference on Issues in Philosophical and Mathematical Logic, in Devonport, New Zealand, 11–12 May 1991, at a South West Logic Workshop in Seattle, Washington, 20 July 1991, and at a meeting of the Florida Philosophical Association in Boca Raton, Florida, 8 November 1991. We wish to thank all who offered comments at those gatherings. An earlier version of the paper appeared in the Auckland Philosophy Papers series of the Department of Philosophy, University of Auckland, in May 1991.