Hayek I and Hayek II: From Mises's Methodology to Popper's Methodology

Even within the corpus of Hayek's own work a distinction may be made. A scholar who distinguishes two different strains of thinking within Hayek's own writing was Hutchison. He labels the early publications as Hayek I (before 1936) and the later ones as Hayek II (1937 and thereafter). Of the earlier period Hutchison states: "Affinities with the ideas of Austrian predecessors, notably with those of his 'mentor' Mises, are apparent." In  contrast, the first publication of the latter period (Hayek 1937), Hutchison comments:

It certainly marks a vital turning point, or even U-turn, in Hayek's methodological ideas, and ought to be, but has not been recognized as marking a fundamental shift . . . The main insights of this article are quite incompatible . . . with the methodological ideas in his previous writings.

The new dispensation in Hayek had mainly to do with a shift from praxeological (e.g., Misesian) methodology to that based on logical positivism (e.g., Popper), and from an emphasis on appraisement to one of lack of full information regarding questions of central planning and socialism.

--Walter Block and Kenneth M. Garschina, "Hayek, Business Cycles, and Fractional Reserve Banking: Continuing the De-Homogenization Process," Review of Austrian Economics 9, no. 1 (1996): 79.