What "rule of reason" for the EU Internal Market?

From a general point of view, it can be argued that legal reasoning encompasses the concept of reasonableness, been as the establishment of a set of rules necessarily implies allowing a margin of flexibility. The latter may take one of several forms, ranging from exceptions and derogations to exemptions. Either way, a comparison of different competing values will need to be applied by the legislator, executive or the judiciary. As far as competition law is concerned, the so-called “rule of reason”, a notion of elasticity allowing for exceptions from a rigid rule to be established, was developed in US antitrust law long before the creation of the European Union. The aim of this paper is to determine whether such a concept can play a role in the EU internal market and to analyse if, and how, it has been applied in that context. A response to such a legal conundrum will be given by effecting a comparative analysis of two distinct facets, namely the market rules dealing with competition and those linked to the free movement of goods, persons, services and capital