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The adversarial system (or adversary system) of law is the system of law, generally adopted in common law countries, that relies on the skill of the different advocates representing their party's positions and not on some neutral party, usually the judge, trying to ascertain the truth of the case. The inquisitorial system that is usually found on the continent of Europe among civil law systems (ie. those deriving from the Roman or Napoleonic Codes) has a judge or a group of judges who work together whose task is to investigate the case before them.
Judges in an adversarial system tend to be more interested 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 adversary 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), and it was not until 1963 that the U.S. Supreme Court declared that legal counsel was a fundamental right of felony defendants in state courts. See Gideon v. Wainwright, Template:Ussc.
One of the most significant differences between the adversary system and the inquisitional 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 inquisitional 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.
 History of the adversarial process
Some writers trace the adversarial process to the medieval mode of trial by combat, in which some litigants, notably women, were allowed a champion to represent them. Certainly the use of the jury in the common law system seems to have fostered the adversarial system, and there are many today who believe that it remains the best way of providing for the determination of a disputed issue. On the other hand, the new British Civil Justice reforms initiated by Lord Woolf (the Civil Procedure Rules or CPR) are prefaced with a case management system controlled by the judge rather than by the lawyers representing the different parties; similar case management systems are coming into use in the United States.
The adversarial system also disposes of the canard whereby lawyers are often asked how they can represent someone if they believe that person to be guilty (or innocent for that matter, although this might be a more difficult position): 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.
 Basic features of the adversarial system
As an accused is not compelled to give evidence in a criminal adversarial proceeding he may not be questioned by prosecutor or judge unless he chooses to do so. However, should he decide to testify, he is subject to cross-examination and can be found guilty of perjury. As the election to maintain an accused person's 'right to silence' prevents any examination or cross-examination of that person's position, it follows that the decision of counsel as to what evidence will be called is a crucial tactic in any case in the adversarial system and hence it might be said that it is a lawyer's manipulation of the truth. Certainly, it requires the skills of counsel on both sides to be fairly equally pitted and subjected to an impartial judge.
By constrast, 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.
The passive role of the judge in the adversarial system also allows for plea bargaining in which the defendant agrees to plead guilty in exchange for a lesser sentence by the prosecution, or for out of court settlements in civil cases. In practice, most cases in the United States are disposed of in this manner. In the inquisitional system, plea bargaining is impossible because there is no concept of a plea, and any attempt for the prosecution and defense to negotiate a sentence without the involvement of the judge would be considered highly unethical.
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 Britain, the Criminal Justice and Public Order Act 1994 allowed such inferences to be made for the first time. 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.
 Comparisons with the inquisitorial approach
In many jurisdictions the approaches of each system are often formal differences in the way cases are reviewed. It is questionable that the results would be different if cases were conducted under the differing approaches; in fact no statistics exist that can show that these systems do not come to the same result. However, these approaches are often a matter of national pride and there are opinions amongst jurists about the merits of the differing approaches and their drawbacks as well.
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. 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 the prosecution to bring charges far in excess of what is warranted and the defense 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.
Furthermore, some countries with an inquisitorial system do use jury trials for some categories of crime. Interestingly, some countries such as Japan before 1943 which used to have a right to jury trial, rarely used them, as there is a popular belief that any defendant who requests a jury trial has a case that is so weak that they are willing to risk pleading their case before strangers rather than professional judges. Hence, jurors in those countries are very unsympathetic toward defendants. (Jury system in Japan was suspended in 1943. In 2004, whole new lay-judge system was enacted in Japan and will be installed in 2009. In this system, 6 jurors and 3 judges will discuss and judge a case together.)he:השיטה האדברסרית