How is a social decision made out of individual members' decisions? This is one of the primary questions in the social sciences. Logic and Social Choice provides an answer to the topic by the application of mathematical logic. Yasusuke Murakami formulates social decision-making in logical terms, and shows that an analysis of social decision is equivalent to a logical calculus in many-valued logic. The logical conditions are then derived for various types of societies, especially for democracy. This foundation enables the author to discuss such topics as the relation between direct democracy and the representative system, a comparison of various rules of election, and the stability of social decision. The main conclusion is that inconsistency or paradox is inherent not only in voting and in democracy itself, but also in any piecemeal social decision-making.