 Hook’s enduring commitment to Deweyan pragmatism contributed to his ultimate rejection of Marxism. The understanding of verification in pragmatic theory as requiring experimental confirmation of hypotheses by an appeal to derived, predictable consequences illuminated crucial dissimilarities between pragmatism and a Marxist theory of verification through revolutionary activism in societal transformation. Further, the interpretation of the scope and limits of scientific method in the attainment of knowledge led to a clarification of the extreme difficulties, insuperable in methodological terms, between the establishment of a natural science and the realization of a “science of history.” Thus Hook’s continuing commitment to the exploration of Deweyan pragmatism led him to the abandonment of his support for Marxism. To a degree, Hook’s focus on foundational moral issues shifted by the late 1930s from the investigation of the compatibility of Deweyan pragmatism with Marxism toward the defense of Deweyan ethical naturalism against the tide of opposition from moral absolutism and from moral emotivism.