 Modal fictionalists can certainly respond to the more general worry that fictionalism makes it too arbitrary which particular story about possible worlds ought to be employed. After all, the purposes of the fiction constrain what sorts of fiction are suitable, just as not any old story about a gas will serve to provide an “ideal gas” which has a behaviour approximated by real gases. Some story must be told about what sorts of constraints are appropriate, and why: and this can be difficult in its own right (see the “which fiction should be employed” section, below). Even if there are substantial constraints on what story will be adequate, and these constraints are not due merely to facts about us or our choices, there may still be some scope for the story to be artificial to a small degree, for some points of detail may be left underdetermined by the constraints. This may also be considered a problem, but it is unlikely to be fatal.