 Defenders of dilemmas need not deny all of the pertinent principles. If one thinks that each of the principles at least has some initial plausibility, then one will be inclined to retain as many as possible. Among the earlier contributors to this debate, some took the existence of dilemmas as a counterexample to ‘ought’ implies ‘can’ (for example, Lemmon 1962 and Trigg 1971); others, as a refutation of the agglomeration principle (for example, Williams 1965 and van Fraassen 1973). A common response to the first argument is to deny PD. A more complicated response is to grant that the crucial deontic principles hold, but only in ideal worlds. In the real world, they have heuristic value, bidding agents in conflict cases to look for permissible options, though none may exist (Holbo 2002, especially sections 15–17).