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Evidence in its broadest sense, refers to anything that is used to determine or demonstrate the truth of an assertion. Philosophically, evidence can include propositions which are presumed to be true used in support of other propositions that are presumed to be falsifiable. The term has specialized meanings when used with respect to specific fields, such as policy, scientific research, criminal investigations, and legal discourse.

The most immediate form of evidence available to an individual is the observations of that person's own senses. For example an observer wishing for evidence that the sky is blue need only look at the sky. However this same example illustrates some of the difficulties of evidence as well: someone who was blue-yellow color blind, but did not know it, would have a very different perception of what color the sky was than someone who was not. Even simple sensory perceptions (qualia) ultimately are subjective; guaranteeing that the same information can be considered somehow true in an objective sense is the main challenge of establishing standards of evidence.

Evidence in science

Main article: Scientific evidence

In scientific research evidence is accumulated through observations of phenomena that occur in the natural world, or which are created as experiments in a laboratory. Scientific evidence usually goes towards supporting or rejecting a hypothesis. When evidence is contradictory to theoretical expectations, the evidence and the ways of making it are often closely scrutinized (see experimenter's regress). The rules for evidence used by science is collected systematically in an attempt to avoid the bias inherent to anecdotal evidence.

Evidence in criminal investigation

In criminal investigation, rather than attempting to prove an abstract or hypothetical point, the evidence gatherers are attempting to determine who is responsible for a criminal act. The focus of criminal evidence is to connect physical evidence and reports of witnesses to a specific person.

Evidence in law

Main article: Evidence (law)

Legal evidence differs from the above in the tight rules governing the presentation of facts that tend to prove or disprove the point at issue. In law, certain policies require that evidence that tends to prove or disprove an assertion or fact must nevertheless be excluded from consideration based either on indicia relating to reliability, or on broader social concerns. Testimony (which tells) and exhibits (which show) are the two main categories of evidence presented at a trial or hearing.