 So much for the argument’s main premises. How is it supposed to work? Here we find the suggestion that it hinges on an application of Leibniz’s Law of the Indiscernibility of Identicals (Robinson (1994: 32); Smith (2002: 25)). The point is that (i) and (ii) tell us that in an illusory experience you are directly presented with an F thing, but the ordinary object supposedly being perceived is not F, thus the F thing and the ordinary object are not identical, by Leibniz’s Law. On these grounds, the conclusion of the base case is supposed to follow. And then the ultimate conclusion of the argument can be derived from its further premises.