  This treatment of nonmonotonicity is similar to the earlier modal semantic theories of conditionals—the similarities are particularly evident using the more general theories of conditional semantics, such as the one presented in  Chellas 1975.  Of course, the consequence relation of the classical conditional logics is monotonic, and conditional semantics uses possible worlds, not models. But the left-nonmonotonicity of conditionals (the fact that A  C does not imply [A  ∧  B]   C) creates issues that parallel those in nonmonotonic logics. Early work in nonmonotonic logic does not seem to be aware of the analogy with conditional logic. But the interrelations between the two have become an important theme more recently; see, for instance,  Gärdenfors &amp; Makinson 1994,  Boutilier 1992,  Pearl 1994,  Gabbay 1995,  Benferat et al. 1997,  Delgrande 1998,  Arlo-Costa &amp; Shapiro 1992,  Alcourrón 1995,  Asher 1995,  and  Thomason 2007.