“This has nothing to do with realism (even if it explains also realism). A completely real world can be constructed, in which asses fly and princesses are restored to life by a kiss, but that world, purely possible and unrealistic, must exist according to structures defined at the outset (we have to know whether it is a world where a princess can be restored to life only by the kiss of a prince, or also by that of a witch, and whether the princess's kiss tranforms only frogs into princes or also, for example, armadillos).”