<P> In common law legal systems, the common law is crucial to understanding almost all important areas of law . For example, in England and Wales, in English Canada, and in most states of the United States, the basic law of contracts, torts and property do not exist in statute, but only in common law (though there may be isolated modifications enacted by statute). As another example, the Supreme Court of the United States in 1877, held that a Michigan statute that established rules for solemnization of marriages did not abolish pre-existing common - law marriage, because the statute did not affirmatively require statutory solemnization and was silent as to preexisting common law . </P> <P> In almost all areas of the law (even those where there is a statutory framework, such as contracts for the sale of goods, or the criminal law), legislature - enacted statutes generally give only terse statements of general principle, and the fine boundaries and definitions exist only in the interstitial common law . To find out what the precise law is that applies to a particular set of facts, one has to locate precedential decisions on the topic, and reason from those decisions by analogy . </P> <P> In (common law jurisdictions (in the sense opposed to "civil law"), legislatures operate under the assumption that statutes will be interpreted against the backdrop of the pre-existing common law . As the United States Supreme Court explained in United States v Texas, 507 U.S. 529 (1993): </P> <Dl> <Dd> Just as longstanding is the principle that "(s) tatutes which invade the common law...are to be read with a presumption favoring the retention of long - established and familiar principles, except when a statutory purpose to the contrary is evident ." Isbrandtsen Co. v. Johnson, 343 U.S. 779, 783 (1952); Astoria Federal Savings & Loan Assn . v. Solimino, 501 U.S. 104, 108 (1991). In such cases, Congress does not write upon a clean slate . Astoria, 501 U.S. at 108 . In order to abrogate a common - law principle, the statute must "speak directly" to the question addressed by the common law . Mobil Oil Corp. v. Higginbotham, 436 U.S. 618, 625 (1978); Milwaukee v. Illinois, 451 U.S. 304, 315 (1981). </Dd> </Dl>

Who applies the law in a court case