One of the legal cornerstones of ‘formal federalism’ is the capacity of any rule of EC Law to override any rule, including those of constitutional rank, of the Member States. The primacy doctrine has been introduced by the Court of Justice in Costa v. ENEL (1964). It can be read in two ways. In the first place it may be held to imply the supremacy of Community law, i.e., the idea that Community law has a higher rank than even the national constitutions and is hierarchically superior to it, as the Court itself sometimes has expressed it (Simmenthal, 1978). This may be called the existential reading. Alternatively, there is a more modest interpretation implying mere practical priority or precedence, as in traffic rules. For this practical interpretation there are equally arguments to be found in the Court's case-law: the aims of the EC-treaty cannot be accomplished if domestic law were to prevail over Community law.