In common law legal systems,the common law is crucial to understanding almost all important areas of law. For example, in England and Wales 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）. 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 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. To consider but one example, the First Amendment to the United States Constitution states " Congress shall make no law respecting an establishment of religion,or prohibiting the free exercise thereof"——but interpretation （that is, determining the fine boundaries, and resolving the tension between the "establishment" and "free exercise" clauses） of each of the important terms was delegated by Article III of the Constitution to the judicial branch, so that the current legal boundaries of the Constitutional text can only be determined by consulting the common law.
