"The article aims to investigate one important argument used by the European Court of Justice in order to assess the consistency of National laws with the European social directives; mainly, the effectiveness of Eu law. The reasons are several. Effectiveness is an omnipresent argument in the case law of the Ecj; it is cross-sectoral to different subjects addressed by the Court; it is both an argument systematically employed by the Court and a main objective of Eu social law. The analysis is based on a number of judgments given by the Ecj as a consequence of a request for a preliminary ruling (article 267 Tfeu) and of an infringement procedure (article 258 Tfeu). The selection of the judgments and the analysis of the legal reasoning of the Court are focused on specific interpretations of specific provisions of a number of Directives so as to be more concrete. "

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