Wason's standard 2-4-6 task requires discovery of a single rule and leads to around 20% solutions, whereas the dual goal (DG) version requires discovery of two rules and elevates solutions to over 60%. We report an experiment that aimed to discriminate between competing accounts of DG facilitation by manipulating the degree of complementarity between the to-be-discovered rules. Results indicated that perfect rule complementarity is not essential for task success, thereby undermining a key tenet of the goal complementarity account of DG facilitation. The triple heterogeneity account received a good degree of support since more varied triple exploration was associated with facilitatory DG conditions, in line with this account's prediction that task success is associated with the creative search of the problem space. The contrast class account (an extension of Oaksford & Chater's, 1994, iterative counterfactual model) was also corroborated in that the generation of descending triples was demonstrated to be the dominant predictor of DG success. We focus our discussion on conceptual ideas relating to the way in which iterative counterfactual testing and contrast class identification may work together to provide a powerful basis for effective hypothesis testing.