ABSTRACT
The aim of this investigation is to elucidate the character of the reasons given for attempted solutions to the selection task, or four-card problem (Wason, 1966, 1968a). The problem is now fairly well known. In essence it consists in establishing the truth value of a conditional sentence, e.g., “If a card has a vowel on one side, then it has an even number on the other side”, by selecting for inspection the necessary and sufficient cards from a set consisting of a vowel, a consonant, an even number and an odd number (under the restriction that each has a letter on one side and a number on the other side). The solution is to select the vowel and the odd number because only these two values on the same card could falsify the test sentence; the even number could merely verify it vacuously. But previous studies (with abstract material) have demonstrated that the most frequent erroneous solutions consist in selecting the values mentioned in the test sentence. The problem is recalcitrant to correction (Wason, 1969a), and its difficulty is not restricted to test sentences with the surface structure of a conditional; in a recent version (Wason and Golding, 1974) the sentence is an assertion e.g., “a letter is above each number”.
