Unlike Treaty provisions and regulations, directives cannot have horizontal effect (against another private individual or company), as this is adjudged contrary to the principles of legality and legal certainty (see Marshall v Southampton Health Authority. Furthermore, in the judgments "CIA Security" and "Unilever Italia SpA v Central Food SpA", the ECJ allowed a private party to rely on the Notification Directive against another private party. Academic commentary has typically referred to these cases as involving "incidental effects" of directives against private parties, as opposed to full-blown horizontal direct effect. However, the exact distinction between "incidental effects" and "horizontal direct effect" has proved difficult to draw. According to recent case law and commentary, it appears a directive can be invoked against a private party insofar as this does not affect the norm(s) directly governing the dispute at hand.