As opposed to that, the inquisitorial system usually found on the continent of Europe among civil law systems (i.e., those deriving from Roman law or the Napoleonic Code) has a judge (or a group of judges who work together) whose task is to investigate the case.
The adversarial system is the two-sided structure under which criminal trial courts operate that pits the prosecution against the defense. Justice is done when the most effective adversary is able to convince the judge or jury that his or her perspective on the case is the correct one.
Lawyers are often asked how they can represent someone if they believe that person to be guilty; counsel must not deceive the court but his client is entitled to have the best presentation of the case laid before the tribunal and to have the evidence fully tested. In England and Wales, if a client states his guilt to his counsel, the counsel is required to cease working on the case (assuming the client is pleading innocence).
By contrast, while defendants in most civil law systems can be compelled to give a statement, this statement is not subject to cross-examination and not given under oath. This allows the defendant to explain his side of the case without being subject to cross-examination by a skilled opposition.
Judges in an adversarial system are impartial in ensuring the fair play of due process, or fundamental justice. Such judges decide, often when called upon by counsel rather than of their own motion, what evidence is to be admitted when there is a dispute; though in some common law jurisdictions judges play more of a role in deciding what evidence to admit into the record or reject. At worst, abusing judicial discretion would actually pave the way to a biased decision rendering obsolete the judicial process in question—rule of law being illicitly subordinated by rule of man under such discriminating circumstances.
The rules of evidence are also developed based upon the system of objections of adversaries and on what basis it may tend to prejudice the trier of fact which may be the judge or the jury. In a way the rules of evidence can function to give a judge limited inquisitorial powers as the judge may exclude evidence he/she believes is not trustworthy or irrelevant to the legal issue at hand.
Peter Murphy in his Practical Guide to Evidence recounts an instructive example. A frustrated judge in an English (adversarial) court finally asked a barrister after witnesses had produced conflicting accounts, 'Am I never to hear the truth?' 'No, my lord, merely the evidence', replied counsel.
The name adversary system may be misleading in that it implies it is only within this type of system in which there are opposing prosecution and defense. This is not the case, and both modern adversary and inquisitiorial systems have the powers of the state separated between a prosecutor and the judge and allow the defendant the right to counsel. Indeed, the European Convention on Human Rights and Fundamental Freedoms in Article 6 requires these features in the legal systems of its signatory states.
The right to counsel in criminal trials was initially not accepted in some adversarial systems. It was believed that the facts should speak for themselves, and that lawyers would just blur the matters. As a consequence, it was only in 1836 that England allowed suspects of felonies to have legal counsel (the Prisoners' Counsel Act). In the United States, however, personally retained counsel have had a right to appear in all federal criminal cases since the adoption of the Constitution (a response to the English practice of barring counsel from felony cases) and in state cases at least since the end of the Civil War, although nearly all provided this right in their state constitutions or laws much earlier. Appointment of counsel for indigent defendants was nearly universal in federal felony cases, though it varied considerably in state cases. It was not until 1963 that the U.S. Supreme Court declared that legal counsel must be provided at the expense of the state for indigent felony defendants, under the federal Sixth Amendment, in state courts. See Gideon v. Wainwright, .
One of the most significant differences between the adversary system and the inquisitorial system occurs when a criminal defendant admits to the crime. In an adversary system, there is no more controversy and the case proceeds to sentencing; though in many jurisdictions the defendant must have allocution of her or his crime, a false confession will not be accepted even in common law courts. By contrast, in an inquisitiorial system, the fact that the defendant has confessed is merely one more fact that is entered into evidence, and a confession by the defendant does not remove the requirement that the prosecution present a full case. This allows for plea bargaining in adversary systems in a way that is difficult or impossible in inquisitional system, and many felony cases in the United States are handled without trial through such plea bargains.
Another difference is in the rules of evidence. Because the adversarial system assumes that the evidence is to be presented to laymen rather than to jurists, the rules of evidence are considerably more strict. Rules on hearsay are much stricter in most adversarial systems than in inquisitorial systems; though often lower tribunals are allowed some flexibility in applying the strict rules of common law evidence such as in domestic relations courts or in small claims proceedings where the parties are often unrepresented by lawyers and the judge functions as more of an inquisitor to protect the interests of children than a neutral arbiter of justice.
In some adversarial legislative systems, the court is permitted to make inferences on an accused's failure to face cross-examination or to answer a particular question. This obviously limits the usefulness of silence as a tactic by the defence. In England the Criminal Justice and Public Order Act 1994 allowed such inferences to be made for the first time in England and Wales (It was already possible in Scotland under the rule of criminative circumstances). This change was disparaged by critics as an end to the 'right to silence', though in fact an accused still has the right to remain silent and cannot be compelled to take the stand. In the United States, the Fifth Amendment has been interpreted to prohibit a jury from drawing a negative inference based on the defendant's invocation of his right not to testify, and the jury must be so instructed if the defendant requests.
Proponents of the adversarial system often argue that the system is more fair and less prone to abuse than the inquisitional approach, because it allows less room for the state to be biased against the defendant. It also allows most private litigants to settle their disputes in an amicable manner through discovery and pre-trial settlements in which non-contested facts are agreed upon and not dealt with during the trial process.
In addition, adversarial procedure defenders argue that the inquisitorial court systems are overly institutionalized and removed from the average citizen. The common law trial lawyer has ample opportunity to uncover the truth in a laboratory called the courtroom. Most cases that go to trial are carefully prepared through a discovery process that aids in the review of evidence and testimony before it is presented to judge or jury. The lawyers involved have a very good idea of the scope of agreement and disagreement of the issues to present at trial which develops much in the same way as the role of investigative judges. It has also been argued that a trial by a jury of one's peers may be more impartial than any government paid inquisitor and a panel of his peers. In the United States the right to a trial by a jury of one's peers who are common citizens is guaranteed by the United States Constitution.
Proponents of inquisitorial justice dispute these points. They point out that most cases in adversarial systems are actually resolved by plea bargain and settlement. Plea bargain as a system does not exist in inquisitorial system. Most legal cases in these systems do not go to trial; this can lead to great injustice when the defendant has an unskilled or overworked attorney, which is likely to be the case when the defendant is poor. In addition, proponents of inquisitorial systems argue that the plea bargain system causes the participants within the system to act in perverse ways, in that it encourages prosecutors to bring charges far in excess of what is warranted and defendants to plead guilty even when they believe that they are not. Furthermore, proponents of inquisitorial systems also argue that the power of the judge is limited by the use of lay assessors and that a panel of judges may not necessarily be more biased than a jury.
The adversarial system has also been attacked for failing to accurately resolve complex technical issue such as science, technology, or tax or accounting regulation. In the adversarial system, juries encounter such complex technical cases for the first time. This would lead to unjust outcomes for one or both of the litigating parties due to the lack of understanding of the evidence presented. In the inquisitorial system, the judge, though not an expert in each technical subject, would have gone through similar tax, forensic, or accounting related issues countless times, and are thus unlikely to be confused or manipulated.
Disadvantages of using a Jury on criminal matters include:
This is not an exhaustive list.