Gresham's Law / 劣币驱逐良币

Definition

Gresham’s Law describes the tendency for money with lower intrinsic or trusted value to remain in payment while higher-value money is hoarded, melted, exported, or reminted when the two can discharge obligations on terms that do not reflect their real value difference.

Current Synthesis

The two source branches use the same selection mechanism in different monetary systems. Newton and the Counterfeiter episode 26 applies it to clipped and machine-struck English silver before the Great Recoinage / 大重铸. Hanji 201 applies it analogically to early Han eight-zhu and pod coins: users spend the lighter coin and retain or recast the heavier one. Across both cases, nominal acceptance cannot by itself preserve better coin in circulation when users can profit from selecting it away.

Key Claims

• The law concerns selection between monies treated as substitutable in payment despite different underlying value or trust.
• Inferior money remains visible in circulation because holders preferentially dispose of it.
• Better money can disappear through hoarding, melting, export, or reminting rather than physical nonexistence.
• Minting standards and criminal enforcement cannot work independently of circulation incentives and material control.
• Historical applications require care because legal-tender rules, exchange terms, metal content, and enforcement differ across cases.

Evidence

• English silver crisis: 26.牛顿与伪币制造者：可能是斯内普的原型？ links clipped coin, counterfeit pressure, international metal movement, and selection against better silver coin before recoinage.
• Early Han analogy: Hanji 201 says lighter pod coins stayed in use while heavier eight-zhu coins were collected or recast, helping explain the shift to a lighter five-part issue.
• Enforcement boundary: Hanji 201 argues that severe anti-minting law did not eliminate the incentive or the regional capacity to circumvent it.

Counterevidence & Qualifications

Neither source supplies a formal economic test of every necessary condition. The English episode is a broad book discussion, and Hanji 201 uses a much later named law to explain an ancient bronze-coin reform without establishing all exchange-rate, legal-tender, weight, or market details. The mechanism is therefore a comparative interpretive tool, not automatic proof that the two systems were institutionally equivalent.

What Changed

• Added the early Han coinage branch and distinguished the shared selection mechanism from institutional equivalence.
• Migrated the page to the synthesis-v1 concept contract while preserving the original English source inventory and appending the new source once.

Related Concepts

• 大重铸 - English monetary repair response to degraded silver circulation.
• 货币信用 - broader relationship between nominal value, accepted weight, and public trust.
• 伪币执法 - enforcement response that cannot alone remove selection incentives.
• 早期汉代铸币禁令执行缺口 - early Han case where prohibition and severe penalties do not produce effective monetary control.
• 五铢钱中央统一铸造 - later Chinese mechanism joining mint monopoly, material control, and standardization.