This article seeks to highlight the importance of international law to the realm of international taxation. The article, without, detailing and repeating the obvious and much-written aspects of this interaction and interplay such as the Vienna rules of interpretation, covers an aspect which may be not be apparently obvious to all international tax practitioners. This aspect is how, in certain situations, when tax systems of monist and dualist states interact, double taxation of income may ensue. Double taxation of this kind occurs if there is a mismatch between the performances, by the states, of the respective obligations assumed at the international plane in the form of a tax treaty. A mismatch will easily occur, both if a state does not, either intentionally or unintentionally, give effect to the treaty domestically or if a state, after having implemented the treaty internally, gives superseding effect to domestic tax law, thus overriding a pre-existing treaty. The answer to the question, whether and if to what extent, international obligations may be domesticated and not disturbed subsequently by a state depends on which of the two theories: monism or dualism, has been adopted by that state to define the relationship between its municipal law and international law. The present article concerns itself with examining how double taxation occurs under the first of these scenarios. A brief account of the monist and the dualist theories of international law together with three hypothetical cases, viz., 'permanent establishment case', ' dividend distribution case' and 'dual-resident case' has been included to facilitate better and clearer understanding of the interaction between monist and dualist tax systems and to exemplify the tax consequences of that interaction.
Intertax