Misguided Inferences? The Use of Expressio Unius to Interpret Tax Law

Abstract

This article explores how the interpretive canon of expressio unius has been used by the courts when interpreting the Income Tax Act, and discusses the canon’s place within the landscape of statutory interpretation of income tax law. The article reviews the existing literature to describe the canon, the assumptions on which the canon relies, and the reasons in favour of and against the canon’s use. The ultimate conclusion is there is some value in the interpretive tool, but it should be used only to prompt interpreters to ask questions instead of prompting them to draw conclusions. While canons of interpretation are generally considered textualist in nature, expressio unius type reasoning is often used as a way of taking into account the context of a particular provision. Another problem apparent in the case law is that the canon, also called implied exclusion, is often confused with the canon of implied exception. The article also examines court decisions that apply or reject the use of expressio unius when interpreting the Income Tax Act. Finally, the article proposes factors that should be considered when determining whether expressio unius should be used in a particular tax case.