Bringing reason to a messy doctrine: The distinction between mistake of law and mistake of fact

This article is concerned with the distinction between mistake of law and mistake of fact in criminal law defences. The article criticises the traditional view that distinguishes between mistake of law and mistake of fact by the criterion of perceptibility. The authors argue that the traditional view is over-inclusive and, if applied consistently, would assimilate all cases of mistake into the category of mistake of fact. The modern ‘prohibition-centred’ approach is also criticised, since it suffers from ambiguity as to what counts as ignorance of, or a mistake about the criminal prohibition or its meaning. Following a critical discussion of the rationales for the differential treatment of mistake of law, the authors propose and justify an alternative test that is based on the rationale of promoting compliance with the law. The alternative test is a two-stage test. First, the criminal prohibition must be identified as the conduct rule that derives from all signs that: (a) are made primarily for the purpose of changing the legal situation; and (b) are addressed by the state or its officials to an indefinite group of persons. Second, the two types of mistake must be distinguished as follows: (a) a mistake of law is a failure to infer that the conduct rule, which was identified in the first stage, applies to a given set of facts, where that inference can be made solely on the basis of the meaning of the conduct rule and the facts determining its temporal and territorial effect; and (b) a mistake of fact is a mistake in regard to the existence (or a lack of awareness of the existence) of the set of facts.