The paper raises the issue of a normative justification of the horizontal effect of fundamental rights in private law. Justification in this sense means that the reasons given are neither functional nor instrumental, but that the reasons are supposed to be subject to the intrinsic logic of private law. In traditional doctrine, the reason usually given to confer horizontal effect to fundamental rights is a deferral to the constitution: The constitutional text decides whether and how fundamental rights apply to private legal relationships. This answer implies that fundamental rights are either logically or normatively alien to private law, that they are located in a logical or normative room beyond the logical room of private law. In contrast to this prevailing opinion, the paper argues that, first, private law is logically prior to fundamental rights, and that, second, fundamental rights are part of private law’s intrinsic normative logic. This is developed for the class of democratic rights that includes all rights besides anti-discrimination rights and classical civil rights. If the argument is cogent, then it can also explain why fundamental rights also apply, including horizontal effect, in the sphere of transnational legal regimes, subject to the transnational jurisdiction of state courts and international tribunals.