 If we accept Martin’s account of causally matching hallucinations, then we can see how H can be present in both the hallucinatory and the veridical case: since trivially a veridical experience of a snow-covered churchyard is indiscriminable from a veridical experience of a snow-covered churchyard. But what about screening off? Does H have a nature which means that the presence of H in the veridical case threatens the explanatory power of N? It doesn’t, Martin argues, since H’s explanatory force is derivative or dependent: it is parasitic on that of N. As Martin notes with his own example: