 Walton acknowledges that each principle has counterintuitive consequences (see Walton 1990: ch. 4 on the contrast and interplay between the two principles). Lewis himself noted this in the case of the Reality Principle, but as we remarked above the same seems true of the Mutual Belief Principle. In addition, neither principle seems able to handle cases in which genre conventions generate fictional truths. Consider an otherwise typical zombie story that never explicitly says that zombies move by stumbling forward rather than by running (Woodward 2011: 163). Because this way of moving is a conventional feature of zombies in the zombie story genre, it will be true in the story that zombies don’t run, even though the question “Do zombies run?” is probably not answerable by appeal to either principle (Woodward 2011: 163; Lewis 1978 [1983: 274]; Walton 1990: 161–9). Walton himself thinks that the moral to be drawn from such difficulties is that these principles are no more than rules of thumb, and that there is no single, general principle that governs the practice of critics and appreciators of fiction (1990: 139). A rather different approach to these problems is taken by Stacie Friend, who argues that problems ensue if we insist on principles, taken as ways of inferring implied fictional truths from primary fictional truths. Instead of defending the Reality Principle, she defends what she calls the Reality Assumption, the thesis that everything that is really true is also fictionally the case, unless it is excluded by the work (Friend 2017).