2.3.2.4 Terminology

30. Particularly the literature published in the wake of the judgments in Mangold and Kücükdeveci illustrates and stresses the relevance of a clear terminological framework. In EU doctrine usually the term ‘direct horizontal effect’ (or ‘horizontal direct effect’) is used to pinpoint the effect of the principle of the prohibition of age discrimination in horizontal proceedings in which the compatibility of national legislation is reviewed.1 However, constitutional law and private law literature tend to speak of ‘indirect horizontal effect’.2 After all, the rule of Union law does not directly impose obligations and confer rights on the private parties, and the legal relationship between the private parties – the employment contract – is not directly scrutinised against the principle of the prohibition of age discrimination. What is reviewed is the compatibility of the national legislative provision with this principle. So via – i.e. indirectly – the compatibility review of the national norm against the principle, the legal relationship between private parties is influenced.3

31. In the wake of CIA Security and Unilever the procedural compatibility review has also been labelled as a form of direct horizontal effect. Some authors label the disapplication of national legislation as a result of a procedural compatibility review as the ‘incidental horizontal direct effect of directives’4. Also other terms have been used, such as ‘horizontal side effects of direct effect’5 or ‘disguised vertical direct effect’.6

32. It is somewhat unfortunate that many authors label whichever type of compatibility review of national law against Union law as direct horizontal effect merely because the compatibility review can take place in the context of proceedings between private parties. This use of terminology does not correspond to the actual effect of the rights of Union law conferred upon private parties to the horizontal legal relationship in which a national legislative provision is reviewed. After all, the compatibility review of a national provision does not at all imply the direct interference of the provision of Union law in the horizontal legal relationship. Therefore, the compatibility review of national law against Union law is a type of indirect horizontal effect.7 Whilst, in spite of the foregoing some scholars keep relying on obsolete terminology, others stress the importance to clarify the perspective from which one departs.8 Self-evidently, it would be optimal to ultimately reach a common and coherent terminological framework with which both European law scholars and practitioners as well as private lawyers can work. However, meanwhile, everyone writing – or reading – about the various ways in which Union law impacts legal relationships between private parties should make an effort to clarify from which perspective the publication is written and what the terms used mean.