The doctrine of implied amendment allows that amendments to the Constitution be adopted outside of the constraints of the formal constitutional amendability procedure. Having endorsed the doctrine during the lifetimeof the 1922 Constitution, the Irish courts after 1937 had unambiguously rejected it, for the ‘scant respect’ it showed for the Constitution as superior law as well as the ‘practical disadvantage’ that it made the Constitution unknowable. Nevertheless, this article argues that the doctrine of implied amendment has been enjoying an unremarked revival in the context of the ratification of the European and international treaties, the beginnings of which can be seen in the Crotty decision, then traced through McGimpsey, and are now magnified by the sweeping Pringle decision. In Crotty, the Supreme Court judges not only measured the Single European Act for compatibility with the Constitution – employing a test of constitutional consistency – but they also endorsed the ‘essential scope and objectives’ test – a test of treaty comparison – which compared the SEA for how different it was from the Treaties of Rome. The basic feature of a test of treaty comparison is, simply, that it examines the treaty in question by reference to another treaty in order to assess whether or not it requires a constitutional amendment. Tests of treaty comparison have since been deployed in both the McGimpsey and Pringle decisions, although the indices of comparison may vary widely between judgments. In Pringle, for example, the majority judges seemed to recognise no less than nine new indices by which the test of treaty comparison can be applied. These range from whether future policy-making power of the State is involved to whether foreign policy as a whole is affected; from whether the treaty is abstract or concrete to whether it has a single purpose or multiple purposes. Consideration of the consistency and congruence of these indicies is for another paper; here, the point is that the test of treaty comparison, in principle, allows that amendments to the Constitution can slip through the net because treaties are being measured for similitude with other treaties without regard to their impact on constitutional provisions. This current application of the doctrine of implied amendment in the context of treaty ratification is, it is suggested, certainly no less troubling than its historical use. The more legally defensible option, which avoids the known dangers of the doctrine of implied amendment, is, as the dissentient in Pringle has done, to assess any treaty by reference to the provisions of the Constitution using the test of constitutional consistency.
