We offer a theory and methodology for studying what we call social propensities. A social propensity consists of a social value rule (e.g., MaxOwn, MinDiff, Need) combined with a propensity function (monotonic or non-monotonic) that expresses the rule as a probability of endorsement for a given self:outcome pair. Our approach formalizes and generalizes concepts from interdependence theory, social value orientations, and distributive justice rules, and is applicable in two-person games and exchange situations.