Abstract
Sources of facilitation for Needham and Amado's (1995) Pythagoras version of Wason's THOG problem were systematically examined in three experiments with 174 participants. Although both the narrative structure and figural notation used in the Pythagoras problem independently led to significant facilitation (40–50% correct), pairing hypothesis generation with either factor or pairing the two factors together was found to be necessary to obtain substantial facilitation (> 50% correct). Needham and Amado's original finding for the complete Pythagoras problem was also replicated. These results are discussed in terms of the “confusion theory” explanation for performance on the standard THOG problem. The possible role of labelling as a de-confusing factor in other versions of the THOG problem and the implications of the present findings for human reasoning are also considered.