本稿ではコンドルセが『多数決論』で提出した陪審定理を検討し，社会的決定過程の分析に役だちそうないくつかの含意をみちびくとともに，その限界を指摘する。陪審定理は啓蒙主義の人間観・真理観に制約されている。この結果，陪審定理をもちいてさまざまな価値が錯綜する現実の意思決定過程を分析しようとすると，困難が生じる。それゆえ，今日の社会的選択理論は，コンドルセがいわば窮余の策としてもちいたコンドルセ規則をベースに展開し，陪審定理をかえりみることはすくない。にもかかわらず，社会的決定過程において正しい決定がくだされる確率を探求するコンドルセの議論は，社会的選択理論の今後の発展にとって無視できない課題を示唆している。

In this paper，we will examine the jury theorem which Condorcet proposed in his study on majority decision at 1785. Then，we will clarify not only its useful implications for the studies of collective decisions，but also its limitations. Condorcet's model was too influenced with the views of “humanity” and “truth” in the age of the Enlightenment. Thus，we must encounter many difficulties, if we are going to apply his model to the analysis of today's decision processes，where many values are conflicting with one another. Therefore，recent social choice theories are developing on the basis of “Condorcet's rule” which was only an ad-hoc hypothesis for Condorcet's thought. His main idea，that is，the jury theorem itself is rarely referred. Nevertheless, the jury theorem to explore the probability of the “right” decision will suggest important keys for the progress of the studies on social choices and collective decisions.