The commonplace view is that moral thinking has significantly influenced legal theory, but law has had very little theoretical effect on morality. In this article, I attempt to show this is not so. Taking the inverse course in tracing the interrelations between law and morality – investigating morality from the perspective of law rather than examining law from the perspective of morality – I show, through the case of promises, that legal theory has greatly affected dominant strands of moral thought. By bringing to the fore the robust legal elements that guide some of the prevailing moral theories, my aim is to offer a new diagnosis of their problems, showing that the legal mindset is what distorts their moral analysis.
I start by offering a list of law’s special underpinnings. Predicating law as a unique social phenomenon and, as such, as possessing certain features that distinguish it from other normative domains, this list, though not a definition of law as such, presents a sufficiently inclusive account of what it means for a normative theory to be legal or legal-oriented. This profile serves as a tool helping to discern, for the first time, the unrecognized influences of legal thinking on other normative domains, and to reveal whether, and to what extent, some normative accounts rest on and are affected by legal ideas, tools, terminology, and structure. Applying this model to the analysis of promises offered by such thinkers as Charles Fried, John Rawls, and T. M. Scanlon, I show how their legal mindset shapes their moral accounts of promises. My conclusions indicate that the unaccounted for influence of legal ideas on morality in general, and on the morality of promises in particular, leads to an unsatisfactory conception of both.