Proportionate defence in morality and law

Speaker: Professor Jeff McMahan, University of Oxford
Chair: Professor George Letsas & Professor Riz Mokal, UCL
Admission: Free
Series: Social & Legal Philosophy Colloquia 2015

About this colloquium

Proportionality is a concept that is far more complex than is generally appreciated. It is often conflated, especially by international legal theorists, with the notion of necessity, which is itself more complex than most people recognise. McMahan’s paper endeavors to explain precisely what the differences are between proportionality and necessity as constraints on defensive action. There are, moreover, several distinct forms of proportionality in defence, only one of which is generally acknowledged in the law of war.

Confusion about proportionality is particularly rife in discussions of the morality and law of war. Most theorists, for example, suppose that the good effects that count in the assessment of in belloproportionality are different from those that count in the assessment of ad bellum proportionality. McMahan argues not only that this leads to paradoxes – for example, that a war that is disproportionate could consist entirely of acts of war that are all individually proportionate – but also that the in belloproportionality condition in law is incoherent. He also attempts to elucidate the distinction between proportionality in defence and proportionality in punishment, seeking in addition to explain how liability differs from desert.

The paper concludes by explaining some of the many ways in which proportionality is a distinctively deontological (as opposed to consequentialist) constraint on defensive action.

About the speaker

Jeff McMahan is White’s Professor of Moral Philosophy at the University of Oxford. He completed a BA degree in English literature at the University of the South (Sewanee), followed by graduate work in philosophy at Corpus Christi College, Oxford as a Rhodes Scholar. Professor McMahan then studied at the University of Cambridge, where he was a research fellow of St. John’s College from 1983 to 1986 and received his doctorate in 1986.

He has written extensively on normative and applied ethics. His publications include The Ethics of Killing: Problems at the Margins of Life (Oxford University Press, 2002), Killing in War (OUP, 2009), which argues against foundational elements of the traditional theory of the just war, The Morality of Nationalism (co-edited with Robert McKim, OUP, 1997), and Ethics and Humanity (co-edited with Ann Davis and Richard Keshen, OUP, 2010).

Download the paper