Utilitarianism has frequently been criticized for lacking psychological realism, but what this means and why it is thought to matter varies. This article distinguishes and examines three main relevant kinds of appeals to psychological realism: (a) A minimalist, self-avowedly metaethically neutral and empirically based ‘ought implies can’ approach, exemplified by Owen Flanagan. (b) Arguments from psychological costs and flourishing, exemplified by Michael Stocker and Bernard Williams. (c) ‘Thick’ psychological realism, exemplified by Elizabeth Anscombe, where a conception of human nature does (...) not simply provide constraints on value theory, but forms the substantive basis on which it builds. The main challenge raised for utilitarianism turns out to be metaethical, not a matter of empirical psychology. The question is not so much whether utilitarianism can accommodate (putative) descriptive facts of human psychology as such, but what normative weight these facts should be given and why. [ABSTRACT FROM PUBLISHER] Copyright of Utilitas is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to alls.). (shrink)