Hayek was too harsh on Freud. It is, indeed, one of the surprising facts of the development of intellectual thought during the twentieth century that… - Alan O. Ebenstein

During World War II it was exciting and unexpected for Hayek to find someone else, from Vienna, who was interested in many of the same topics that he was. The Open Society and Its Enemies has three main parts, on Plato, Hegel, and Marx. The next main chapters in Hayek’s uncompleted “The Abuse and Decline of Reason,” on which he was at work then, were to be on Hegel and Marx. In addition, Popper’s scholarly style was similar to Hayek’s, with extremely extensive notes.

His epistemology began from a phenomenalist base. The philosopher and physicist Ernst Mach was very important in Hayek’s development and to the atmosphere at the University of Vienna when Hayek was a student there.

Hayek truly did get Popper his position at the London School of Economics. “I am personally anxious to get Dr. Popper to this School,” Hayek wrote Gombrich as early as 1943. Given the later prominence that Popper achieved for the school, this was one of Hayek’s most significant contributions to its reputation, as well as the decisive career move in Popper’s life.
Hayek also genuinely influenced Popper’s political philosophy. While Popper always remained to Hayek’s left, he started out much further to Hayek’s left than he wound up, and this movement was in no small part the result of Hayek’s influence. Popper was a charter member of the Mont Pelerin Society. He suggested, however, that socialists be brought into it. Hayek wrote Popper several deeply personal letters in connection with his divorce. It is likely that their personal relationship was more important to and valued by Hayek than Popper, though Popper valued highly Hayek’s friendship.