This chapter constructs a theoretical model for understanding cultural change by revisiting and extending Ludwik Fleck’s key concepts of thought collectives and thought styles. Rejecting single-determinant models of transformation, it emphasizes Fleck’s account of socially conditioned perception and comparative epistemology, which foregrounds the interactive, collective nature of knowledge formation. Through a systematic analysis of Fleck’s writings from 1929 to 1936, the chapter traces the development of key notions—including intellectual unrest, collective mood, and the circulation of ideas—from an initial emphasis on individual creativity toward a more sophisticated account of collective cognition. The chapter argues that Fleck’s framework must be revised when extended to broader socio-cultural categories such as class, race, and nation, highlighting how collective identities are discursively constructed. It also clarifies key differences between Fleck’s thought styles and Kuhn’s paradigms, particularly the distortions and transformations that occur when knowledge circulates across group boundaries. Fleck’s notion of intellectual unrest is shown to provide a fruitful means for analysing external determinants of change—including the Vesalian turn to dissection, the role of print technology, and the institutional formations of early modern universities. By exploring how such external and internal pressures destabilize established epistemic configurations, the chapter demonstrates how knowledge circulation between thought collectives can trigger reconfigurations of a thought style. Through these historical case studies, Fleck’s comparative epistemology is extended beyond the confines of science to encompass broader processes of cultural transformation.