The author examines the horizontal effect of fundamental rights, and the link between this constitutional doctrine and the distinction between private and public law. The author argues that the horizontal effect of fundamental rights justifies the need to somehow redefine the dualism of private and public law, not as two separate sets of rules or subsystems in law, but as distinct methods of legal regulation which are partly based on tradition and partly arise as a product of idealised abstraction, and which can overlap in various ways in practical situations.