The entangled dynamics leading to the sedimentation of polarisation on political Reddit

Summary

This paper examines 16 years of activity across 11 major political subreddits to investigate whether cross-ideological communication actually occurs on Reddit. Through a battery of overlap measures — shared domains, URLs, cross-posting, cross-commenting, subreddit links, and discursive identities — the authors find strikingly low cross-community interaction, even among ideologically aligned subreddits. They argue that polarization on Reddit is not produced by discourse, platform affordances, moderation, or user behavior alone, but by their entanglement. Drawing on Laclau’s notion of sedimentation, they reconceptualize polarization as a precondition of political subreddit activity rather than its outcome: communities operate as if already in opposition to all others, regardless of discursive similarity.

Key Contributions

• Introduces the concept of “sedimentation of polarisation” — polarization as a discursive-digital condition that precedes rather than results from communicative practice.
• Develops a Normalised Similarity Score (NSS) that compares observed cross-community overlaps to expected overlaps, controlling for subreddit size and activity.
• Provides large-scale empirical evidence that r/politics is not a cross-ideological “town square”, contradicting a recurring framing in Reddit research.
• Extends polarization research beyond the left-right binary by documenting fragmentation among ideologically similar communities (e.g., r/Conservative vs. r/conservatives).
• Advances a non-hierarchical framework integrating platform design, moderation, user agency, and discourse as inseparable co-constituents.

Methods

A mixed-methods design combining computational overlap analysis with corpus-assisted discourse analysis. The authors compute NSS scores across six dimensions (shared domains, URLs, linked subreddits in submissions and comments, cross-submitting and cross-commenting users) for all subreddit pairs. Keyness analysis in AntConc 4.3.1 (using r/politics as the reference corpus) characterizes the discursive identity of each subreddit. Two coders thematically analyze subreddit descriptions, rules widgets, and wikis to map moderation regimes, including the role of AutoModerator.

Findings

• No subreddit pair reached NSS ≥ 1.0 on shared domains; the highest overlap (r/progressive–r/DemocraticSocialism at 0.879) collapsed to 0.094 at the URL level, indicating different stories are shared from common sources.
• Cross-posting never exceeded NSS = 0.206; cross-commenting never exceeded 0.280 — users rarely leave their homebase.
• r/politics shows uniformly low overlap with both left- and right-leaning subreddits, undermining both the “left-leaning bias” claim and the public-sphere framing.
• Right-leaning subreddits cohere around shared antagonists (“woke,” “the left,” “cancel culture”), while left-leaning ones display greater topical diversity (gun control, electoral politics, economic reform, Marxist critique, anti-Trump resistance).
• Strict-moderation subreddits (r/Liberal, r/Republican) show little derogatory language; loosely moderated ones (r/republicans) feature slurs like “libtards” and “demoncraps.”
• The split of r/conservatives from r/Conservative demonstrates that intra-ideological polarization can be produced by moderation conflicts alone.

Connections

This paper speaks directly to work questioning whether cross-cutting exposure produces deliberation or its opposite, complementing Bakshy2015-rn’s foundational work on exposure and Rossini2026-jn on cross-ideological dynamics. Its emphasis on moderation and platform materiality as co-constituents of polarization resonates with Copland2025-em and Esau2025-tf, while its critique of the public-sphere framing aligns with broader reassessments in Gaisbauer2025-by and Kristensen2025-ni. The focus on Reddit as an under-studied site of political fragmentation also connects to platform-comparative work like Efstratiou2025-gs.

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