How did legal positivism become influential during the 20th century?

Legal positivism became the dominant framework in 20th-century philosophy of law primarily through the influential, yet distinct, theories of Hans Kelsen and H.L.A. Hart.12

Kelsen sought to explain the normative force of law—its claim to authority—without relying on moral justification. Influenced by Neo-Kantian philosophy, he proposed a "pure theory" of law, arguing that legal validity ultimately rests on a foundational "basic norm" (Grundnorm).3

Hart later shifted the focus by rejecting command-based theories. He argued that legal systems are defined by a "rule of recognition," a social rule established by the conventional practices and attitudes of officials, particularly judges. This "impure" positivism grounded legal authority in observable social facts rather than transcendental presuppositions.4

The influence of these thinkers was further cemented by Joseph Raz, who refined the positivist framework by emphasizing the "service conception" of authority and the necessity of source-based criteria for legal validity. Throughout the century, these developments established positivism as the central point of reference for legal theorists, including those who developed antipositivist or realist responses.512