Measuring the Semantic Structure and Evolution of Conspiracy Theories

TL;DR

This study analyzes how conspiracy theories' meanings change over time in online discourse, using large-scale Reddit comments and semantic analysis techniques.

Contribution

It introduces a method to measure the semantic evolution of conspiracy theories as distinct semantic objects over a decade.

Findings

Conspiracy-related language forms coherent, distinguishable semantic regions.

Conspiracy theories evolve non-uniformly with stability, expansion, and replacement.

Semantic analysis reveals changes not captured by keyword approaches.

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 measure 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 demonstrate that conspiracy-related language forms coherent and semantically distinguishable regions of language space, allowing conspiracy theories to be treated as semantic objects. We then track how these objects evolve over time using aligned word embeddings, enabling comparisons of semantic neighborhoods across periods. Our analysis reveals that conspiracy theories evolve non-uniformly, exhibiting patterns of semantic stability, expansion, contraction, and replacement that are not captured by keyword-based approaches alone.