Subtracting Reasons in Normative Domains

Abstract

Practical reasons can be aggregated to decide what one ought to do. This paper explores an operation that undoes aggregation: subtraction. I consider several distinctions concerning subtraction: subtracting content and subtracting strength; and subtracting one reason from one other reason or from a set of reasons. I put forward a precise understanding of subtracting the content of one reason from another, based on an operation of difference on a state-like, structured notion of content. Finally, I apply my approach to subtracting reasons to normative domains, and in particular to belief revision and norm change.