In civil proceedings in the common-law countries, evidence is both ascertained and simultaneously restricted by the assertions of the parties. If the allegations of one party are not disputed or contested by the other, or if the allegations are even admitted, then no proof is required. Proof would, in fact, be irrelevant. Evidence offered to prove assertions that are neither at issue nor probative of the matter at issue would also be irrelevant. The only evidence that is, therefore, relevant, is evidence that to some degree advances the inquiry and has a probative value for the decision. While continental European judges, in ordering the hearing of evidence or in deciding on evidence, indicate the facts to be proved and thereby strictly eliminate irrelevant facts, Anglo-American judges first give the parties an opportunity to furnish any evidence that they deem suitable. If, during the hearing of witnesses, irrelevant questions are put, they are rejected after the adversary has objected to them.

It has been said that relevance depends on logical considerations and that admissibility depends on the law. In contrast to civil law, the common law has developed a large number of rules governing the admissibility of evidence. Relevant evidence is not admissible, for example, if the witnesses are excluded from testifying because of incompetency, or if they are protected by privileges against self-incrimination, or in instances in which they would have to divulge confidential or professional communications that have a privileged status or government secrets, or, again, when the evidence is excluded by the rules against hearsay (see below Witnesses).

In criminal cases in civil-law countries, relevance relates to such questions that are so far removed from the case that they have no evidence value at all. Admissions and confessions do not exclude further evidence. According to Anglo-American law, the accused may be a competent witness under the admissibility rules, but, in contrast to an ordinary witness, he has the privilege of not taking the witness stand. According to continental European law, the accused is neither a party nor a witness. He can be heard, but he cannot be forced to answer questions of fact. In general, Anglo-American rules of admissibility apply to criminal proceedings much as they apply to civil cases.

The free evaluation of evidence

Freedom to evaluate all the evidence produced was established in Roman law but fell into disuse as a principle during the time of the formalistic Roman-canonical law of evidence that characterized the Middle Ages. Remnants of the medieval formal theory of evidence survive in various countries.

In countries where remnants of the medieval formal theory of evidence are still preserved, the principle of free evaluation of the evidence by the judge generally dates from the French Revolution. The French introduced the concept of the judge’s conviction intime (inner, deep-seated conviction) in contrast to rules of formal evidence that prescribed exactly when the evidence amounted to proof. The primacy this gave to the personal conviction of the judge meant that it was not even necessary to state the reasons for the inner conviction. This total dependence on the judge’s discretion aroused a great deal of criticism, and, as a result, various judicial codes prescribed that, in giving the grounds on which judgment was based, the judge had to specify in writing why he was convinced in each case. Conviction intime in its original sense is limited to the testimony of witnesses and experts and to the explanations of the parties. Both kinds of formal oaths made by parties to a case, the supplementary oath and the tendered oath, are still valid in civil-law countries, and both may lead to formal solutions, since the judge must follow the legal consequences of the oath. But these survivals of medieval formal evidence theory have been weakened. In France, for example, the judge’s latitude under the principle of conviction intime has been extended to allow him to pass on the affirmation oath of the party, which formerly had to be given a certain value, regardless of his opinion of its worth. In other countries, such as Austria, Germany, and the Scandinavian countries, the formal oath of the parties was abolished and replaced by the free depositions of the parties. Even if the parties take an oath on their testimonies during this process, the judge is not bound by it but may still make his own evaluation of the evidence. In addition, some remnants of the formal evidence theory have been preserved with regard to documentary proof where rules of procedure contain presumptions as to the conclusiveness of certain documents. Since reliance on documentary evidence prevails in some countries, these formal evidence rules are still of special importance.

In Anglo-American law the problem of free evaluation of evidence can be understood through the institution of the jury. Obviously, the evidence must be convincing to the common sense of the jury members, who form their judgment on the basis of free conviction. The function of the jury, however, is to decide questions of fact rather than questions of law, which are left to the judge. The jury’s verdict can be overturned by the judge if it is inconsistent with the evidence or with his instructions as to the law governing the case. The judge’s relationship to the jury therefore plays a role in the decisions, and there are difficult questions in which it is unclear whether the jury or the judge should consider the evidence. Some formal rules of evidence survive in Anglo-American law. In some cases evidence must be corroborated before it can constitute proof. In homicide cases, for example, a confession must be supported by additional evidence. In addition, evidence by witnesses is sometimes excluded by rules of admissibility.