A previous study (Nakagaki 1987) has shown that the thematic material effects on logical reasoning, caused by illogical problem-solving strategies, were more apparent than real. This effect has been explained by the “degeneration theory” proposed by the author. The present study was designed to examine possible degeneration effects on the abstract four card problem (FCP), when the card form or the conditional sentence (p→q) was modified. Three types of abstract FCPs were administered to 88 high school students; the standard FCP, a FCP containing a card expressing explicitly the negation of the consequent(q), and a FCP having a conditional sentence with a double negative form (p→q). The subjects performed significantly better on the second and third types of aostract FCPs than on the standard one. This result was in accordance with the prediction of the “degeneration theory” and confirmed the degeneration effects even on abstract FCP. Based on this evidence, it was concluded that the matching bias in abstract FCP (Evans et al. 1973) could be better interpreted from the standpoint of the “degeneration theory” and that the thematic material effects on realistic FCP and the high performance of some tasks in abstract FCPs, having been thought to be caused respectively by different reasoning strategies, could both be systematically explained by the “degeneration theory.”.
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