- **Money, credit, and contract as institutionalized promises** (Simmel, *The Philosophy of Money*; Ingham). Currency is trust made fungible.
- **Reputation systems and repeated games** (Axelrod; folk theorem). Cooperation is sustainable when interactions repeat and defection is punished.
- **Institutions as trust infrastructure** (North; Fukuyama, *Trust*). Legal systems, auditors, ratings agencies, and regulators are the economy's *immune system* — evolved responses to endemic deception.