2.1.2 Horizontal effect

18. As indicated, Union law does not only confer rights upon private parties, but also imposes obligations upon them. Consequently, the question arises how a private party can invoke rules of Union law against another private party that has failed to comply with its obligations under Union law. Not all rules of Union law that can be invoked directly against a Member State can likewise be invoked against another private party. On the contrary, the effect of rules of Union law in horizontal legal relationships is in most cases different from the effect of Union law in vertical legal relationships, not only in relation to the way in which a rule of Union law can be invoked in or applied to the specific legal relationship, but also in relation to the way in which the concrete legal consequences of the effect of the rule of Union law are determined. In conclusion, the term direct effect as such does not provide for the desired refinement related to the differences between vertical and horizontal effect. In itself, the term horizontal effect is indistinctive too. It solely indicates that a rule of Union law has a certain impact on a horizontal relationship, but does not specify in which way. Therefore, the term horizontal effect is divided into direct horizontal effect and indirect horizontal effect.