DEVELOPMENTAL-CHANGES IN CATEGORY-BASED INFERENCES

Category-based inferences were divided into two types: the downward in ference which the category terms in the conclusion are lower than thos e in the premise and the upward inference which the former terms are h igher than the latter ones. Three tasks were provided for each inferen ce. Kindergartners, second graders, and college students were required to answer to the conclusion statements with ''Yes'' or ''No'' and to justify the answers. The mean number of the positive answers (''Yes'') increased with ages for the downward inference while for the upward i nference it was the largest for the 2nd graders, For the students the mean number was significantly greater for the downward than for the up ward inferences. The findings were discussed with acquisition and use of three types of knowledge; for the downward inference the inclusive knowledge that the conclusion category terms are included in the premi se ones, and for the upward inference the associative knowledge that t he premise category terms are associated to the conclusion ones and th e inclusive knowledge that the conclusion category terms include some category terms other than the premise ones.