**Topic:**

**GENERAL LOGIC**

## The Modal Logic of Agreement and Noncontingency

Lloyd Humberstone

The formula DA (it is noncontingent whether A) is true at a point in a Kripke model just in case all points accessible to that point agree on the truth-value of A. We can think of D-based modal logic as a special case of what we call the general modal logic of agreement, interpreted with the aid of models supporting a ternary relation,

S, say, with OA (which we write instead of DA to emphasize the generalization involved) true at a pointwjust in case for all pointsx, y, withSwxy,xandyagree on the truth-value of A. The noncontingency interpretation is the special case in whichSwxyif and only ifRwxandRwy, whereRis a traditional binary accessibility relation. Another application, related to work of Lewis and von Kutschera, allows us to think of OA as saying that A is entirely about a certain subject matter.Keywords: modal logic; contingency; noncontingency; subject matters; supervenienceSource: Notre Dame J. Formal Logic Volume 43, Number 2 (2002), 95-127.