Evidence is often presented in a tense, emotional atmosphere in a courtroom long after the event in question took place. The object of the law of evidence is to assure a high probability that questions of fact are resolved correctly. To that end, material introduced at the trial is ordinarily restricted to items of great probative value; that which may arouse unreasoning passion is ordinarily excluded. The nature of the legal controversy and the written pleadings determine what assertions of fact each party must prove or disprove to win the case, and an item of evidence that at best has a remote bearing on the factual issues must be excluded as irrelevant or immaterial. A judge prefers direct evidence (such as an official document or a witness's assertion of immediate knowledge of the question at issue) to indirect or circumstantial evidence, which merely tends to establish the issue by proving surrounding circumstances from which the principal fact may be inferred.
In addition to being relevant, evidence must be competent, i.e., it must not fall under an exclusionary rule. Obviously if the evidence is documentary (e.g., a birth certificate introduced to prove a person's age) or if it is "real" (e.g., a bloody garment exhibited to prove that the victim suffered injury), there can be a question only whether the proffered evidence is itself incompetent. The courtroom presentation of documentary evidence has been complicated by new computer technologies and the digitalization of information, which make the successful forging of texts and photographs far easier than previously.
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