In every case there are allegations made. In a civil case, they are made by the party known as the plaintiff while in a case involving criminal law, the party making the charges or allegations is the prosecutor who is employed by the state jurisdiction in which he practices. If the case involves federal law, the prosecutor is the U.S. Justice Department, a federal agency.
In order to win the case, the plaintiff, or whoever is making the allegations, must make his case by showing the allegations are true according to a given standard of proof to the satisfaction of a jury. For example, Smith alleges that Jones negligently backed his car into Smith, breaking his leg. In order to prove the allegations to be true, Smith must present evidence based on facts and testimony.
The facts that Smith is able to prove are true are then applied to see if the four elements necessary for Smith to win are proven. These elements in this negligence claim are the issues that the judge will submit to the jury. The issues are: did Jones owe a duty to be reasonably careful to Smith, did Jones breach or violate that duty, was this violation by Jones of his duty to Smith the cause of Smith’s broken leg, and did Smith actually have his leg broken.
In its role as a fact finder, a jury decides, based on the evidence presented, what is the truth in regard to the facts of the case. The jury will decide on the above four issues based on the facts they have found to be true, and if their answer is yes to all four of these issues, Smith wins. In determining what their conclusion is to each of these issues, the jury is given considerable discretion even when evidence regarding the same fact conflicts to the extent that opposite inferences could be drawn. This discretion even extends to cases in which the facts are undisputed; different inferences could still be found by a rational jury.
However, the judge still has discretion to withhold from the jury the right to decide a particular issue if he believes the evidence is insufficient for the jury to come to a reasonable conclusion. Because each of the issues that Smith must prove in his favor to the jury are essential to his case, a decision by the judge that the evidence presented is not enough to support only one of the four issues would result in Smith losing the case.