The adversarial system is the two-part system under which criminal law courts operate. On one side is the prosecution who usually represents the government. The other side is the defense who represents the defendant. Each party may call witnesses and ask questions. Each party may present evidence based on legal ethics and that is approved by the court. For example, legal ethics prevent a lawyer from calling a witness they know will lie on the witness stand. Justice is served when the most effective adversary is able to convince the jury or judge that his or her case is the correct one.