Common law is a body of unwritten laws based on legal precedents established by the courts. It is derived from judicial decisions, customs, and usages rather than from statutes or constitutions. This system, also known as case law, relies on the principle of stare decisis—"to stand by things decided"—where past judicial decisions guide the resolution of current disputes. Its authority stems from the accumulated judgments of courts over time, which interpret and apply principles to new factual situations, contrasting with civil law systems that are based on codified statutes.

A. Civil law: This legal system relies on comprehensive, written codes and statutes enacted by a legislature, not on judicial precedent or custom.

B. Commercial sales: This is a specific area of contract law (e.g., governed by the Uniform Commercial Code in the U.S.), not the foundational legal system described.

C. Global Contracts: This term refers to a category of agreements that cross international borders, not a system of law derived from custom and judgments.

1. National Contract Management Association. (2019). Contract Management Body of Knowledge (CMBOK) (6th ed.). Section 1.1.1, Legal Authority. The CMBOK explains that common law, or case law, is a primary source of contract law in the United States, developed from court decisions over centuries.

2. Garner, B. A. (Ed.). (2019). Black's Law Dictionary (11th ed.). Thomson Reuters. p. 346. Defines common law as "The body of law derived from judicial decisions, rather than from statutes or constitutions."

3. Cornell Law School Legal Information Institute. (n.d.). Common Law. Wex Legal Dictionary/Encyclopedia. Retrieved from https://www.law.cornell.edu/wex/commonlaw. This resource states, "Common law, also known as case law, is a body of unwritten laws based on legal precedents established by the courts."