We define prenormal modal logics and show that S1, S1, S0.9, and S0.9 are Lewis versions of certain prenormal logics, determination and decidability for which are immediate. At the end we characterize Cresswell logics and ponder C. I. Lewis's idea of strict implication in S1.

This paper looks at the concept of neighborhood canonicity introduced by BRIAN CHELLAS [2]. We follow the lead of the author's paper [9] where it was shown that every non-iterative logic is neighborhood canonical and here we will show that all logics whose axioms have a simple syntactic form-no intensional operator is in boolean combination with a propositional letter-and which have the finite model property are neighborhood canonical. One consequence of this is that KMcK, the McKinsey logic, is neighborhood canonical, (...) an interesting counterpoint to the results of ROBERT GOLDBLATT and XIAOPING WANG who showed, respectively, that KMcK is not relational canonical [5] and that KMcK is not relationally strongly complete [11]. (shrink)