Kelsen, the Principle of Exclusion of Contradictions, and General Anti-­Avoidance Rules in Tax Law

The philosopher Hans Kelsen is most famous for his "pure theory of law", expounded in his book of that name. For most of his scholarly life, Kelsen argued that, as part of the pure theory, two norms that contradict one another within the same legal system breach the philosophical principle of exclusion of contradictions and therefore cannot both be valid at the same time. On some occasions he went further and argued that neither of two such norms can be valid. Famously, Kelsen changed to the opposite opinion later in life. Both Kelsen's original and his ultimate positions on the principle of exclusion of contradictions shed light on an area of law that he never considered: general anti-­avoidance rules in income tax law, known as "GAARs". GAARs are increasingly common in tax statutes.
One cannot argue that GAARs give rise to what logicians call contradictions. Nevertheless, from a practical and substantive point of view the effect of a GAAR could loosely be described as akin to a contradiction of norms, in logical terms a breach of the principle of exclusion of contradictions. For instance, a GAAR may prevent a taxpayer from relying on a relieving provision in a tax statute, on the grounds that such reliance amounts in the circumstances to tax avoidance. For this kind of reason, people criticise GAARs because they are seen as breaching the principle of certainty, one of the foundations of the rule of law. General principles in Kelsen's work shed light on the way in which GAARs operate and on the way in which they fit into the legal systems of which they form part. Although the effect of a GAAR has something in common with the effect of a breach of the principle of exclusion of contradictions, the unusual nature of tax law justifies the existence of GAARs.