The Rise and Expressions of Consistency in EU Law: Legal and Strategic Implications for European Integration

The principle of consistency has a prominent place in EU law. In the Treaty of Lisbon, it constitutes an umbrella under which a number of legal principles of EU law follow as corollaries. Consistency manifests itself within both horizontal and vertical levels of governance. This chapter will unpack this principle and will focus on the broader implications of consistency for the division of powers in EU law. In doing so, the authors aim to discuss the rise of consistency in EU law and decrypt its various constitutional expressions in order to determine its scope of application. Two notions of consistency are presented: a formal one that appears in the Treaty of Lisbon and a strategic one, prominent in the case law of the Court of Justice of the European Union (CJEU). It is argued that consistency is relevant to both traditional (integrationist) and alternative (differentiated) routes to European integration. The chapter concludes by discussing whether the undefined nature of ‘consistency’ puts it at risk of becoming an empty vessel.