How is the rule of precedent used in today's system of law?
One of the fundamental principles in American law is encapsulated in the Latin phrase stare decisis et non quieta movere, which loosely translates to "to stand by decisions and do not change what is settled." This phrase establishes the principle of precedent in our legal system, and precedent is so important that it's fair to say that even most litigators spend more of their time doing research than they do in court arguing cases.
Precedent in the context of litigation is paramount: the goal of an attorney is to find a case decided in the past, with the outcome that he or she wants for his or her case, whose facts mirror the facts of a new case at issue. If, for example, you've ever marveled at pictures of law offices with books lining every available wall, you have seen the concept of precedent in practice. Those books contain the history of all cases heard by all level of courts in the United States, and attorneys and legal assistants spend most of their working lives looking at those books for cases that resemble their own or, more likely, they are using on line databases that now replace print.
In our legal system, the first level of court, a trial court, is obligated to by guided by decisions made by a higher court, in this case, an appellate (appeals) court, and the Supreme Court. If one of these higher courts establishes a precedent in a decision of a particular case, the associated trial courts have to guide their own decisions by the precedent. So, the precedent for a particular case can come from decisions in prior cases with identical or very similar issues, or it can be established by a higher court--if the original decision is appealed to a higher court, and the higher court overturns the original court's decision, the higher court has set the precedent that other courts must follow.
The US Supreme Court, although not bound by even it's own precedent, even adhere to it unless societal changes appear to mandate it. I am mainly talking about Landmark decisions.
They have overturned themselves about 200 times since thier 1789 inception though, but mostly non Landmark or Historic.
One example of an important ruling is, in Wolf v. Colorado, 1949, although the SC applied/incorporated the 4th AM to the states, it declined to do so with the Exclusionary Rule.
in 1961, Mapp v. Ohio, they overturned themsleves in Wolf and applied the ER to the states.
One criteria to decide whether to grant Certiorari, (hear an appeal), from the Rules of the Supreme Court itself, is when 2 or more Sister Circuit's conflict in a ruling on the same subject matter.
Under Article 6's Supremacy Clause, sister circuits are not bound to follow the ruling of another, they need only adhere to the precedent of the US SC.
The same with a state SC. If they are ruling on a matter a federal appeals court in thier jurisdiction ruled on previously, they do not have to follow that ruling, since Article 6 does not bind them to the same ruling.