Thinking the Impossible [Special Issue]
Issue: Issue 04 • Author/s: Graham Priest
Topics: Epistemology, History of Analytic Philosophy, Philosophical logic
The article looks at the structure of impossible worlds, and their deployment in the analysis of some intentional notions. In particular, it is argued that one can, in fact, conceive anything, whether or not it is impossible. Thus a semantics of conceivability requires impossible worlds.
S4 to 5D [Special Issue]
Issue: Issue 04 • Author/s: Takayashi Yagisawa
Topics: Philosophical logic
The modal logical axiom 4 is widely accepted. It is the characteristic axiom of the modal logical system S4, which is subsumed under the most popular modal logical system S5. Axiom 4 is equivalent to ◇◇P → ◇P (“If possibly possibly P, then possibly P”), which requires that the accessibility relation between worlds be transitive. There is a powerful argument (Hugh Chandler 1976, Nathan Salmon 1981, 1989) against axiom 4. It rests on the thought that an ordinary object could have had a slightly different origin from its actual origin but…