The Development of Class Inferences Based on Categories

Inferences are assumed as processes which one draws some conclusions from the premises. The inferences in which the premise and the conclusion statements have category terms are called the category-based class inferences. The purpose of this study was to examine developmental changes in cognitive processes in the category-based class inferences. There are two types of inferences. For the upward inference the category terms in the conclusion are higher than those in the premise, e.g. , Ekuri (novel word) is a kind of dogs. Is ekuri an animal?" For the downward inference the conclusion terms are lower than the premise ones, e.g., "Karani (novel word) is a kind of animals. Is karani a dog?" The three tasks were provided for each inference. Kindergartners, second graders, and college students were given six inference tasks and required to answer to the conclusion statements with "Yes" or "No" and to justify the answers. The mean number of the positive answers ("Yes") was greater for the upward than for the downward inferences, and for children (kindergartners and second graders) than for students. The interaction was significant, which showed that the mean number in the downward inference was greater for children than for students while the mean number in the upward inference was about the same for the three groups. For the upward inference the percentages of the subjects who made the positive answers to the three tasks consistently were greater for students than for children. For the downward inference those who made the negative answers ("No") consistently were greater for students than for children while those who respond to the three tasks inconsistently were greater for children than for students. The findings suggest that cognitive processes in children's class inferences are different from those in adults' class inferences. The associative knowledge that the conclusion terms are recalled from the premise terms are mainly used in children's upward and downward inferences. Two types of inclusive knowledge are mainly used in adults' inferences: for the upward inference the inclusive knowledge that the premise terms are included in the conclusion terms and for the downward inference the inclusive knowledge that the premise terms include some category terms other than the conclusion terms