[The development of category based induction: five- and six-year-old children's plausibility judgement for general arguments].

The purpose of this study was to investigate preschoolers' ability in judging the plausibility of arguments in Category Based Induction. Experiment 1 was conducted to clarify whether five- and six-year-old children could judge plausibility of general arguments by analyzing the inclusive category of conclusion. The effect of premise typicality, premise diversity, and premise monotonicity of general arguments were examined for this purpose. All the three premise effects were found in six-year-old children, while only the effect of premise monotonicity was found in five-year-old children. In Experiment 2, the effect of premise non-monotonicity was tested to clarify whether children could judge plausibility of arguments by recognizing an inclusion relationship between premise and conclusion categories. The effect of premise non-monotonicity was found in five-year-old children, though it was not perfect. The results of the two experiments suggest that development of Category Based Induction can be divided into two stages. At first, "category based" induction, which means that children can judge plausibility of arguments by recognizing inclusion relationship between premise and conclusion categories, is established from five to six. Later, "category structure based" induction, which means that children can judge plausibility of arguments based on analysis of inclusive category of conclusion, is achieved six and above.