 As well as conformity with our pre-theoretic modal judgements and inclusion of an encyclopedia of actual non-modal truths, Rosen 1990 mentions another source of information to apply in specifying the modal fiction. We have practices of forming modal beliefs involving imagining situations in accord with principles of recombination, non-arbitrariness, and so on (p. 339-40). Rosen points out that while a realist has the challenge of explaining why this practice of imagining should be a guide to modal truth, the fictionalist need not face this challenge if those practices are part of the process of constructing the fiction of possible worlds. If the constraints, or limits, on our imaginative practices when considering hypothetical situations are vital in our practice of making many of our modal judgements, it would make sense to similarly constrain the modal fiction.