The emphasis on equity in the American legal systems is in direct contrast to the civil law principle of legal certainty. In certain civil law systems, judges are often prohibited from making law in the interest of legal certainty. The decisions of judges are perceived as introducing elements of subjectivity or inconsistency into the law, disturbing any systematization of legal principles crafted by the legislator. The legislation should be clear, complete, and coherent, basically judge-proof, creating legal certainty for society. This is in contrast to the institution of equity, which authorizes the judge at her discretion to mitigate the harshness of a strict application of a statute, reinforcing the distinction often made in the United States between “the spirit of the law” and “the letter of the law.”
In the United States, legal certainty is discussed but in more functional terms and not elevated to the level of legal dogma as in some civil law systems. It is achieved in American legal systems by giving the force of law, through stare decisis, to judicial opinions that then become a body of concrete, detailed examples of legal rules in operation. Little difference can be seen, for example, between a civil law system that has integrated case law and the risks involved with respect to legal certainty, and the use of case law within the American legal systems. In the United States, total legal certainty is not perceived as attainable or perhaps even desirable.