Measuring the Semantic Structure and Evolution of Conspiracy Theories

Abstract

Research on conspiracy theories has largely focused on belief formation, exposure, and diffusion, while paying less attention to how their meanings change over time. This gap persists partly because conspiracy-related terms are often treated as stable lexical markers, making it difficult to separate genuine semantic changes from surface-level vocabulary changes. In this paper, we measured the semantic structure and evolution of conspiracy theories in online political discourse. Using 169.9M comments from Reddit’s r/politics subreddit spanning 2012-2022, we first demonstrated that conspiracy- related language forms coherent and semantically distinguishable regions of language space, allowing conspiracy theories to be treated as semantic objects. We then tracked how these objects evolved over time using aligned word embeddings, enabling comparisons of semantic neighborhoods across periods. Our analysis revealed that conspiracy theories evolve non-uniformly, exhibiting patterns of semantic stability, expansion, contraction, and replacement that are not captured by keyword-based approaches alone.