A jury instruction is a guideline given by the judge to the jury about the law they will have to apply to the facts they have found to be true. The purpose of the instructions is to help the jury arrive at a verdict that follows the law of that jurisdiction. In his instructions a judge may explain the legal principles pertaining to the subject matter of the case, make it clear to the jury the legal issues they must decide in order to arrive at a verdict, point out what each side must prove in order to win, and summarize the evidence he sees as relevant and explain how it relates to the issues they must decide. For example, do the facts admitted as evidence and found credible by the jury according to the preponderance of the evidence combined with the application of the legal principles of negligence law warrant a finding by the jury that Smith owed a duty to Jones to be reasonably careful in operating his car?
In giving these instructions, the judge binds the jury. The judge makes clear to the jurors that they are to apply the law to the facts as he gives it to them; they are not to substitute their own judgment as to whether a different law should be applied or whether the law as has been explained to them is unjust. The instructions are to be given in terms a layperson can easily understand. In order to help the jury understand the instructions, the judge may give pre-instructions prior to the time immediately following the presentation of both sides of the case. However, the judge is forbidden to comment on the evidence presented in the case. It is the jury’s responsibility to independently evaluate the evidence.