To the pursuit of judgment formation theory from the pursuit of preference aggregation theory: Toward construction of a new theory of collective decision making for democratic society

There are two different problems of collective decision making in a democratic society. One is the problem of aggregating individuals' preferences into the social preference. The other is the problem of forming the social judgment based on individuals' judgments. In order to solve each of these problems, we must use some theory and method suitable for each. The previous research of collective decision making inclines too heavily towards preference aggregation. We need to recommend research of judgment formation. What characteristics have two types of theory and method? How relevant is the study of judgment formation to recent research trends in some fields around a democratic decision? How significance has it in modem times? The purpose of this paper is to get some tentative answers to each of these questions by reviewing the history of research of collective decision making form ancient Greece to the present age. The opinion of this paper does not already have a preference aggregation theory in the point of being unnecessary, but has the point that it is necessary to recommend the pursuit of a judgment formation theory and has such theories in the point of having a complementary relation for democratic determination.