Ethics-first metaphysics: normative considerations as evidence for ontological commitments

Arjun Devanesan argues that competing mereological accounts of pregnancy have important metaethical implications.[1] Although no particular ontology of pregnancy entails a specific position on abortion or other ethical questions, different views constrain which analogies can plausibly support ethical arguments.Mereological assumptions therefore shape the structure of ethical reasoning, even if they do not determine its conclusions.This is an important advance over the view that metaphysical debates are ethically irrelevant.I argue, however, that the relationship between ontology and ethics is even more intimate than Devanesan suggests.Ontological commitments do not merely constrain ethical arguments from the outside; I suggest that, where biological evidence underdetermines competing ontologies, considered normative judgments may themselves constitute evidence for choosing between them.Recent work on the metaphysics of pregnancy has highlighted the ethical significance of competing ontological accounts.Whether the fetus is a proper part of the pregnant person, a distinct organism merely contained within her, or stands in some intermediate mereological relation has been argued to shape debates concerning abortion, prenatal harm, bodily rights, birth, and ectogenesis.Debates between Colgrove, Hershenov, Kingma, Robinson, and Romanis mentioned by Devanesan (see references 17-18 and 22-27) typically proceed by first