This article argues that Bentham was committed to attempting to measure the outcomes of rules by calculating the values of the pains and pleasures to which they gave rise. That pleasure was preferable to pain, and greater pleasure to less, were, for Bentham, foundational premises of rationality, whilst to abjure calculation was to abjure rationality. However, Bentham knew that the experience of pleasure and pain, the ‘simple’ entities which provided his objective moral standard, was not only subjective, and only indirectly accessible to the legislator, but also typically dependent on a complex of socially mediated beliefs and attitudes. All moral reasoning involved a process of inference from contingent ‘facts’ which was littered with possibilities for error. The Bentham who emerges is a more vulpine hedgehog than is usually allowed, whose core insistence is that, despite its imperfections, consequentialist analysis and decision-making remains the only viable route to a rational morality.