[1] The law of evidence is also concerned with the quantum (amount), quality, and type of proof needed to prevail in litigation.
[3][4] Ancient Roman law allowed freedom to judges to evaluate evidence, but insisted that "proof is incumbent on the party who affirms a fact, not on him who denies it" and "no-one should be convicted on suspicion".
Building on the Biblical two-witness rule, it concluded that a single witness, or private documents, could constitute half-proof, which though insufficient for conviction might justify torture to extract further evidence.
[7] While much of the early common law evidence rules came from judicial decisions, the English Parliament also played a role.
In 1677, Parliament and the Crown enacted the Statute of Frauds and Perjuries, prohibiting plaintiffs from alleging certain contractual breaches to the jury unless accompanied by a signed, written instrument.
Another early evidence rule was the prohibition on hearsay, the admission of an out-of-court statement to prove the truth of what is asserted.
In the early 19th Century, Chief Justice Lord Mansfield of the Court of Common Pleas stated: "In Scotland and most of the continental states, the judges determine upon the facts in dispute as well as upon the law; and they think there is no danger in their listening to evidence of hearsay, because, when they come to consider their judgment on the merits of the case, they can trust themselves entirely to disregard the hearsay evidence, or to give it any little weight which it may seem to deserve.
But in England, where the jury are the sole judges of the fact, hearsay evidence is properly excluded, because no man can tell what effect it might have upon their minds.
In every jurisdiction based on the English common law tradition, evidence must conform to a number of rules and restrictions to be admissible.
"[9] Federal Rule 403 allows relevant evidence to be excluded "if its probative value is substantially outweighed by the danger of unfair prejudice", if it leads to confusion of the issues, if it is misleading or if it is a waste of time.
For example, evidence that the victim of a car accident was apparently a "liar, cheater, womanizer, and a man of low morals" was unduly prejudicial and irrelevant to whether he had a valid product liability claim against the manufacturer of the tires on his van (which had rolled over resulting in severe brain damage).
[10] The United States has a very complicated system of evidentiary rules; for example, John Wigmore's celebrated treatise on it filled ten volumes.
[11] James Bradley Thayer reported in 1898 that even English lawyers were surprised by the complexity of American evidence law, such as its reliance on exceptions to preserve evidentiary objections for appeal.
[11] Some legal experts, notably Stanford legal historian Lawrence Friedman, have argued that the complexity of American evidence law arises from two factors: (1) the right of American defendants to have findings of fact made by a jury in practically all criminal cases as well as many civil cases; and (2) the widespread consensus that tight limitations on the admissibility of evidence are necessary to prevent a jury of untrained laypersons from being swayed by irrelevant distractions.
[11] In Professor Friedman's words: "A trained judge would not need all these rules; and indeed, the law of evidence in systems that lack a jury is short, sweet, and clear.
The majority of people now reject the formerly-popular proposition that the institution of trial by jury is the main reason for the existence of rules of evidence even in countries such as the United States and Australia; they argue that other variables[clarification needed] are at work.
[15] In systems of proof based on the English common law tradition, almost all evidence must be sponsored by a witness, who has sworn or solemnly affirmed to tell the truth.
Otherwise types of evidentiary rules specify the standards of persuasion (e.g., proof beyond a reasonable doubt) that a trier of fact—whether judge or jury—must apply when it assesses evidence.
For example, if a defendant is alleged to have illegally transported goods across a state line by driving them from Boston to Los Angeles, the court may take judicial notice of the fact that it is impossible to drive from Boston to Los Angeles without crossing a number of state lines.
Spoliation is usually the civil-law/due-process variant, may involve intent or negligence, may affect the outcome of a case in which the evidence is material, and may or may not result in criminal prosecution.
Tampering is usually the criminal law variant in which a person alters, conceals, falsifies, or destroys evidence to interfere with a law-enforcement, governmental, or regulatory investigation, and is usually defined as a crime.
Depending on the circumstances, acts to conceal or destroy evidence or misrepresent its true origins might be considered both tampering and spoliation.