Judges decide multiple types of disputes, including disputes involving the property or contractual rights of two private parties (their ‘private rights’). The nature of these private rights has long been the focus of philosophical debates between conventionalists, non-conventionalists, and Kantians. In this article, I offer an argument in favour of the adoption of a legalist concept of private rights by judges and lawyers involved in private law disputes. According to this argument for private law legalism, judges and lawyers should see these rights as purely legal rights that do not reflect any pre-existing moral entitlements but are simply the upshots of positive law. The reason for adopting this legalist view is that it contributes to the rationality, predictability, and stability of legal reasoning, as well as to an appropriate evaluative stance toward positive law. Thus understood, the argument for legalism is not an argument about the nature of private rights, but about the conception of such rights that participants in private law reasoning ought to adopt.