 Perhaps the least controversial candidate for a defining feature of logic is its topic neutrality. A logical principle is valid in any kind of discourse, no matter what kind of objects this discourse is concerned with. For instance, modus ponens is valid not only in physics and mathematics but in religion and in the analysis of works of fiction. Frege captures the idea nicely when he says that a logical principle is valid in “the widest domain of all; […] not only the actual, not only the intuitable, but everything thinkable” (Frege 1884: 21). Thus, whereas the principles of physics are valid only in the actual world and in worlds that are nomologically similar to it, the principles of logic govern everything thinkable. If one of these principles is denied, “complete confusion ensues” (ibid.).