CONCEPT
Modularity Principle
The architectural prescription — drawn from Perrow's later work and extended by AI safety researchers — that systems designed as loosely coupled modules with limited interaction pathways absorb failures that tightly integrated systems transmit catastrophically.
Modularity is the structural antidote to the interactive complexity and tight coupling that Perrow's framework identifies as the architectural sources of normal accidents. A modular system is one whose components are designed as independent units with well-defined interfaces and limited interaction pathways. Modules that are not connected cannot transmit failure between them. The system's overall complexity may remain high, but its effective coupling is reduced because failures are contained within the module in which they originate. The principle extends naturally to AI safety, where the LessWrong community's 2025 analysis proposed Just-In-Time Assembly — temporary assembly of AI capabilities for specific tasks, disassembly afterward — as a direct application of Perrow's later prescriptions.
In The You On AI Field Guide
The modularity principle was central to Perrow's later work, particularly The Next Catastrophe. His shift from procedural to structural prescriptions reflected four decades of observation that procedural safety interventions degrade under pressure while architectural constraints persist. A