Between Concept Formation and Elucidation: Refining the Boundaries of Extremism, Populism, and Conspiracism

The rise of extreme political forces worldwide has fuelled a growing body of research. One caveat of this field is that extremism is often studied alongside neighbouring concepts like radicalism and populism as well as in combination with either left or right ideologies. Moreover, its conceptualization remains contested across within-case constructivist studies – focusing on the interpretative construction of the term within groups – and cross-case comparative research – focussing on its distinction from radicalism and populism, although boundaries remain blurred. To address these lacunae, we propose a two-stage conceptual framework. First, we introduce a 'weakest-link' conceptualization that integrates micro-, meso-, and macro-level characteristics of extremism, bridging constructivist and comparativist approaches. Second, we offer a dynamic perspective on extremism clarifying its boundaries to radicalism, thin-centred and thick ideologies (including populism), and the often overlooked concept of conspiracism. Given the role of extreme ideologies in populism research and conspiracy narratives in radicalization, it is essential to understand their link to extremism while avoiding conceptual stretching in comparative research. By refining extremism's boundaries, our approach enhances conceptual clarity and methodological rigor.