Pain is a paradigm of an intrinsically bad mental state: It is an experience that is harmful to those who undergo it and makes their life go worse. Virtually all moral theories recognize norms to assist those who suffer from pain and to avoid inflicting unnecessary pain on others, though there is some disagreement about the source of these norms, their exact content, and their scope. The moral status of the pain of animals, for instance, remains a matter of controversy.

Pain has ethical significance when it is understood as an affective experience that is unpleasant or disliked in itself. Thus understood, pain belongs to a family of distinct but overlapping evaluative notions such as distress and suffering. The word "pain," however, is also used to refer to a type of bodily sensation typically associated with damage to body tissue. We normally...