Chapter 2 Direct and indirect horizontal effect

14. This book covers questions of private law and Union law. The question whether a rule of Union law confers a right upon a private party, is distinguished from the question whether a private party can invoke that right against a Member State or another private party. The latter question depends on the effect of the particular rule of Union law.1 The terminology on the effect of rules of Union law is far from univocal. Since much has been written about the interpretation and use of these terms,2 I restrict myself to providing a terminological guideline for this specific study.