While there is extensive analysis of proportionality in public law, little has been written about this subject in private law. This paper fills this gap in the literature by engaging in a comparative analysis of proportionality in private and public law, using the illegality defence, a crucial doctrine in private law, as a case study. In doing so, this paper clarifies, critiques and cautions against the use of proportionality in the illegality defence. Importantly, it demonstrates how the use of proportionality in the illegality doctrine is structurally similar to the proportionality requirements in public law. This comparison allows us to: clarify the indeterminate contents of the proportionality requirements in the illegality doctrine; specify their differences from those in public law; and demonstrate how the use of proportionality in the illegality defence is open to criticisms of indeterminacy, incommensurability and rights-based reasoning that have been levelled against its use in public law.
Lim, Ernest and Urbina, Francisco Javier, Understanding Proportionality in the Illegality Defence (February 10, 2018). (2020) 136 Law Quarterly Review, forthcoming.