An institution is viewed as an arrangement of the society through which various social states emerge as outcomes from the actions and interactions of individuals belonging to the society. Following an earlier contribution by Pattanaik and Suzumura (Oxford Economic Papers 48:194–212, 1996), we subscribe to the view that the ethical desirability of an institution is based on the goodness of the outcomes emerging from individuals' actions and interactions via the institution as well as the intrinsic attractiveness of the institution itself. In this paper, we explore the structure of an individual's ethical evaluations of institutions. For this purpose, we discuss how social choices are made through institutions given profiles of individual preferences over social states, propose several a priori properties of institutions and examine their plausibility, and introduce and discuss a lexicographic maximin rule for evaluating institutions ethically. [ABSTRACT FROM AUTHOR]