Author: Y. Seo (@momotarou / Japan)Role: Metanist — Human × AI Understanding ArchitectAI Collaboration: AI Understanding SupportORCID iD: https://orcid.org/0009-0005-7669-0612 Abstract This paper extends Trust Instability Structures by introducing the framework of Legitimacy Collapse Mechanisms, examining structural dynamics through which systems, institutions, and governance architectures experience erosion of perceived validity, authority stability, and coherence-maintenance capacity. While legitimacy traditionally functions as a stabilizing meta-layer enabling compliance, coordination, and systemic predictability, trust-unstable environments characterized by responsibility diffusion, attribution ambiguity, and coherence volatility may generate endogenous pressures undermining legitimacy persistence. Legitimacy failure may not originate in misconduct. It may emerge from structure. 1. Legitimacy as a Coherence Stabilizer Legitimacy enables: Authority recognition Normative acceptance Coordination alignment Compliance predictability Conflict suppression Stable trust underpins legitimacy durability. 2. Defining Legitimacy Collapse Mechanisms Legitimacy Collapse Mechanisms refer to: Structural processes through which systems lose perceived validity, normative authority, and coherence-regulating effectiveness under conditions of persistent trust instability. Collapse may be gradual or discontinuous. 3. Sources of Legitimacy Erosion Erosion pressures may arise from: Trust volatility Responsibility diffusion Interpretive divergence Signal saturation effects Control instability Perception coherence destabilizes. 4. Legitimacy Without Stable Trust When trust destabilizes: Legitimacy shifts from durable systemic acceptance toward fragile situational tolerance. Authority becomes conditional. 5. AI-Integrated System Effects AI-integrated environments intensify collapse dynamics via: Decision opacity Rapid behavioral adaptation Attribution ambiguity Governance lag effects Legitimacy recalibration accelerates. 6. Stability Implications Legitimacy collapse may generate: Compliance inconsistency Coordination breakdown Governance stress amplification Systemic fragmentation Coherence failure regimes Collapse propagates nonlinearly. Conclusion Legitimacy Collapse Mechanisms reframe institutional instability as an emergent structural consequence of trust instability, distributed agency, and coherence-governance limits. Future civilization architectures may require legitimacy-preservation designs emphasizing transparency buffers, attribution stabilization, coherence regulation, and trust regeneration mechanisms. ※ Series Declaration This work is part of the Understanding Capitalism series. The series explores value formation, cognitive mediation, and structural transformations of economic perception.