The dual scale model of weighing reasons

0. Introduction Ethical theory is steeped in two related metaphors: reasons have weight and reasons are weighed on a balance scale to determine an act’s deontic status (e.g., whether an act is permissible, impermissible, or required). Such metaphors are implicit in the ubiquitous talk of outweighing and the balance of reasons. The ubiquity of these metaphors gives them importance. If we are going to use or reject them, we should understand the best way of cashing them out. We may find, as I argue in this paper, that we can construct a promising model of how reasons interact to determine deontic status simply by cashing them out carefully. I assume that the metaphors of weight and weighing are apt for morality and practical rationality. So understood, substantive moral (rational) theories can make two kinds of mistake. First, a theory might incorrectly weight reasons. Perhaps, for example, it overestimates how much weight morality gives to self-interest. Second, a substantive theory might weigh reasons incorrectly. In principle, a theory might make one kind of mistake without making the other. This paper is after the fundamental model of weighing reasons to determine a deontic status, the model that determines what it is to weigh reasons correctly. Such a model can represent any normative theory that correctly weighs reasons, even if the theory incorrectly weights them. It can’t represent any theory that incorrectly weighs reasons. By identifying what it is to weigh reasons correctly, the fundamental model identifies structural constraints on any substantive moral or rational theory. The metaphor of weighing reasons brings to mind a single (double-pan balance) scale. The reasons for φ (Rφ) go in one pan and the reasons for ~φ (R~φ) go in the other. The relative weights, as indicated by the relative heights of the two sides of the scale, determine the deontic status of the act.