Economists have formally modeled moral dispositions by directly incorporating into utility analysis concern for the well-being of others.  But sometimes moral dispositions are not preferences, as connoted by utility analysis, but rather are ingrained as (internal) constraints.  I present a model fleshing out this distinction:  If morl dispositions are internal constraints on a person's real goal of pursuing her self-interest, she will be keen to self-servingly gather, avoid, and interpret relevant evidence, for the purpose of relaxing this constraint and pursuing her self interest.  This gives rise to self-serving biases in moral reasoning.  I show that this alternative model has some implications different from a standar utility model.  Specifically, because a person seeks to avoid information that interferes with her self-interest, the scope for social influence in moral conduct is greater than it is in the conventional model.  Outside parties can improve a person's moral conduct by a) forcing her to receive certain information, b) discouraging her from (selectively) thinking about other information, or c) encouraging her to think through moral principles before she knows where her self interest lies.