Introduction

The author examines some problems that deontically accessible worlds raise for the standard deontic logic (SDL) semantics of ought to do statements. Although different versions of SDL semantics give differing accounts of deontically accessible worlds, all versions suffer from a similar cluster of problems. Deontic alternative worlds are defined as possible worlds in which all people always do what they ought to do. People are assured by SDLS5 that there is at least one deontic alternative world. Such a world would surely be unlike this one, but, because of the humble facts mentioned in the preceding paragraph, the difference must not be too great. SDL semantics then requires that deontic alternative worlds must be all but indistinguishable from the real world. It must contain the same people, the same relevant circumstances, and the same obligations. The restriction of deontic alternative worlds to branching worlds makes sense of SDL semantics.