Private Law Theory

ABSTRACT
This chapter examines in comparative perspective the constitutional doctrine of horizontal effect as it relates to speech and data privacy on social media platforms. In the United States, the fundamental right to free speech is conceptualized as a negative right directed against the state. But whereas protecting private speech against government restrictions is the core concern of the First Amendment, other constitutional regimes go beyond the strict limits of individual rights applying only against the state. In those systems, rather than applying only ‘vertically’ as between the individual and the state, fundamental rights may also have ‘horizontal’ effect as between private parties, including both individuals and corporations. Representative of this approach, the German Federal Constitutional Court acknowledged in its seminal 1958 Lüth decision that the fundamental right to freedom of expression reaches into private law. Similarly, the fundamental right to data privacy takes a constitutional dimension in European legal systems and its application among private parties is subject to public law regimes.

Absent a constitutional framework that captures private interactions, recent developments in the United States have produced various approaches to address the social relationships between users and platforms. Most prominent in the speech context, where the state action doctrine prevents enforcement of free speech rights by users against private platforms, is the idea of platforms as common carriers. With respect to data privacy, by contrast, the concept of information fiduciaries, and related duties such as data loyalty, have gained traction.

A global perspective illustrates that a strict public/private divide in the enforcement of fundamental rights hinders capturing the social relationships between users and social media platforms, because modern speech and privacy conflicts there do not manifest between the individual and the state. Horizontal effect doctrine, as this chapter illustrates, is one way to better capture these relationships. The chapter concludes by examining the normative advantages and disadvantages of the horizontal effect framework on social media platforms.

Haupt, Claudia E, The Horizontal Effect of Fundamental Rights (January 1, 2024), in Oxford Handbook on Digital Constitutionalism (Giovanni De Gregorio, Oreste Pollicino, Peggy Valcke eds, Forthcoming); Northeastern University School of Law Research Paper No 444.