The term "cause of action" has a special meaning in the law. It does NOT mean that someone subjectively believes that he or she (or another person) is a victim and another person therefore "owes" him or her some money. Instead, the phrase announces a conclusion of law, i.e. that the known facts meet the requirements of a particular, recognized legal basis for obtaining relief from a court. For some types of perceived injuries, the law does not provide a remedy. In fact it is a fundamental legal principal that the mere fact of injury is not sufficient to prove a cause of action.

Like most fundamental principles of United States law, the rules concerning "cause of action" first developed in the English common law courts. Very early, those courts developed a set of "writs." Each writ contained a standardized series of factual allegations derived from cases in which the courts had granted relief (granted a judgment). After the writ system developed, the common law courts exercised jurisdiction based on the writs. If the actual facts relating to a person's perceived injury did not fit within one of the standard writs, the common law courts would dismiss the case. The earlier common law courts were extremely rigid, which caused many problems. (This was one of the primary reasons why "equity" courts came into being.) While courts are now more flexible, the basic requirement remains. Before a person can obtain a judgment, she or he must prove a legally recognized right to recovery. The conclusion that he or she has done that is expressed by saying that the person has a "cause of action."

Each recognized cause of action has a unique (but generalized) set of requirements. Those requirements are commonly called the "elements" of the cause of action. For common law actions, such as breach of contract or assault, the elements were developed by the courts. If a cause of action is based on a statute, the statute establishes the necessary elements. To obtain judicial relief, a litigant must demonstrate that the facts of his or her situation satisfy every element of a recognized cause of action.

In every court case two questions must be decided, (1) what the actual facts are, and (2) if those facts prove a cause of action. Controversies concerning the first question are known as "issues of fact" and are decided by a jury, or by the judge if there is no jury. Controversies concerning the second question are known as "issues of law" and are decided by the judge (or the judges if the case is on appeal). Questions of fact cannot be the subject of legal research. One cannot determine if a particular traffic signal was red or green by consulting books in a law library. Similarly, questions of law, not fact, are the usual substance of court decisions, such as those excerpted in textbooks.

However, to reach a legal conclusion in any particular case, there must be some resolution (perhaps temporary) concerning the facts. Many cases are decided on "motion to dismiss" or "motion for summary judgment". Those motions question whether the non-moving party has a cause of action. When those motions are made, no jury or judge has yet determined what the facts are. Therefore, to reach a conclusion the court assumes the facts, or at least what the non-moving party might be able to prove, based upon the information before the court. (The assumption is only for the purpose of that particular motion. If the case proceeds, the assumptions are disregarded.) Quite often a court will ask: "Does the plaintiff have a cause of action?" when it really means: "Assuming that it can prove all that it alleges, will the plaintiff have a legal right to a judgment?"

For example: Assume a defendant has filed a motion to dismiss and that the only factual information before the court is what the plaintiff alleged in the Complaint. To decide the motion, the judge assumes that the facts alleged in the complaint can be proven to be true, and that all reasonable factual inferences from those allegations are also true. Then the question is if those assumed facts satisfy the cause of action requirement. In most cases, there is only one contested item. For example, a cause of action for negligence has four elements. The parties may agree that three of those elements exist. Only one element is controverted. The court's decision on that particular element resolves the entire case.

The term "prima facie case" is related to "cause of action". A person has a prima faciecase if that person's version of the facts, if not controverted or disproved, proves a cause of action.

Court decisions, and legal discussions generally, revolve around the "cause of action" idea. Understanding those discussions requires understanding the elements of recognized causes of action.