Introduction

Abstract

Acting under mistake of law means that one is unaware of the wrongfulness of one’s conduct. The postulate “every man is presumed to know the law” has long been the basis for the rule ignorantia legis non excusat, ignorance of the law does not excuse. However, for over half a century this postulate has been questioned because of its harsh outcomes in respect of a blameless defendant. As a result, the presumption is now widely recognised as no longer being irrebuttable. Many legal systems have found ways to respond to the issue of mistake of law, for example by providing for a defence of mistake of law or interpreting certain crime definitions as to require knowledge of the law. A successful defence of mistake of law is generally limited to those defendants who made a reasonable mistake or could not avoid the mistake. It could be argued that international crimes are of such a grave nature that the presumption that everyone knows the law should be irrebuttable. The more serious the alleged crime, the less reasonable or unavoidable the mistake. On the other hand, the fact that not all norms of international criminal law, including justifications, have fully crystallised and the fact that perpetrators are likely to be less familiar with international crimes than with domestic crimes, may warrant non-exclusion of the defence of mistake of law a priori.