A theory of legal presumptions

This article analyzes how legal presumptions can mediate between costly litigation and ex ante incentives. We augment a moral hazard model with a redistributional litigation game in which a presumption parameterizes how a court "weighs" evidence offered by the opposing sides. Strong prodefendant presumptions foreclose lawsuits altogether, but also engender shirking. Strong proplaintiff presumptions have the opposite effects. Moderate presumptions give rise to equilibria in which both shirking and suit occur probabilistically. The socially optimal presumption trades off agency costs against litigation costs, and could be either strong or moderate. depending on the social importance of effort, the costs of filing suit, and the comparative advantage that diligent agents have over their shirking counterparts in mounting a defense. We posit three applications of our model: the litigation rate effects of the 1995 Private Securities Litigation Reform Act, the business judgment rule in corporations law, and fiduciary duties in financially distressed firms.