  Thagard’s argument seems to be that if there is a mind-independent world, then our representations are representations of the world. (He says representations “should be” of the world, but the argument is invalid with the addition of the auxiliary verb.) The world existed before humans and our representations, including our propositional representations. (So history and, Thagard would likely say, our best science tells us.)  Therefore, representations, including propositional representations, are representations of a mind-independent world. The second sentence of the passage just quoted suggests that the only way that coherentists can reject this argument is to adopt some sort of idealism. That is, they can only reject the minor premiss of the argument as reconstructed. Otherwise they are committed to saying that propositions represent the world and, Thagard seems to suggest, this is to say that propositions have the sort of truth-conditions posited by a correspondence theory. So the coherence theory is false.