Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either a) presumed to be true, or b) were themselves proven via evidence, to demonstrate an assertion's truth. Evidence is the currency by which one fulfills the burden of proof.
There are many issues that surround evidence, making it the subject of much discussion and disagreement. In addition to its subtle nature, evidence plays an important role in many academic disciplines, including science and law, adding to the discourse surrounding it.
An important distinction in the field of evidence is that between circumstantial evidence and direct evidence, or evidence that suggests truth as opposed to evidence that directly proves truth. Many have seen this line to be less-than-clear and significant arguments have arisen over the difference.
Burden of proof
The burden of proof is the burden of providing sufficient evidence to shift a conclusion from an oppositional opinion. Whoever does not carry the burden of proof carries the benefit of assumption. Whoever bears the burden of proof must present sufficient evidence to move the conclusion to their own position. The burden of proof must be fulfilled both by establishing positive evidence and negating oppositional evidence.
There are two primary burden-of-proof considerations:
- 1) The question of on whom the burden rests.
- 2) The question of the degree of certitude the proof must support. This depends on both the quantity and quality of evidence and the nature of the point under contention. Some common degrees of certitude include the most probable event, reasonable doubt, and beyond the shadow of a doubt.
Conclusions (from evidence) may be subject to criticism from a perceived failure to fulfill the burden of proof.
Problems in evidence
The theory of evidence is a field wrought with dispute. Many of these disputes stem from the limits of human knowing, a field known as epistemology. Possibly the most salient question of evidence is how, if, and what, one can know. (Or, in other words, the question is to what extent is it even possible to fulfill the burden of proof.) This is the question of evidence's limits. Some believe all evidence to be circumstantial, denying the possibility of direct evidence.
To help deal with this problem, many fields have found it useful to talk about levels of evidence and certainty, particularly the field of law.
Evidence in science
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.
One must always remember that the burden of proof is on the person making the claim. Within science, this translates to the burden resting on presenters of a paper, in which the presenters argue for their specific findings. This paper is placed before a panel of judges where the presenter must defend the thesis against all challenges.
When evidence is contradictory to predicted expectations, the evidence and the ways of making it are often closely scrutinized (see experimenter's regress) and only at the end of this process the hypothesis is rejected: this can be referred to as 'refutation of the hypothesis'. The rules for evidence used by science are collected systematically in an attempt to avoid the bias inherent to anecdotal evidence: nonetheless even anecdotal evidence is enough to reject a theory incompatible with that evidence, if there are sufficient repeated examples.
Evidence in law
In law, the production and presentation of evidence depends first on establishing on whom the burden of proof lies. There are two primary burden-of-proof considerations in law. The first is on whom the burden rests. In many, especially Western, courts, the burden of proof is placed on the prosecution. The second consideration is the degree of certitude proof must reach, depending on both the quantity and quality of evidence. These degrees are different for criminal and civil cases, the former requiring evidence beyond a reasonable doubt, the later considering only what most likely happened. The decision maker, often a jury, but sometimes a judge, decides whether the burden of proof has been fulfilled.
After deciding who will carry the burden of proof, evidence is first gathered and then presented before the court:
In criminal investigation, rather than attempting to prove an abstract or hypothetical point, the evidence gatherers attempt 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. While this is supposedly a non-biased act, detectives sometimes have agendas of their own.
Evidence before the court
Presenting evidence before the court differs from the gathering of evidence in important ways. Gathering evidence may take many forms; presenting evidence that tend to prove or disprove the point at issue is strictly governed by rules. Failure to follow these rules leads to any number of consequences. In law, certain policies allow (or require) evidence to be excluded from consideration based either on indicia relating to reliability, or broader social concerns. Testimony (which tells) and exhibits (which show) are the two main categories of evidence presented at a trial or hearing. In federal court, evidence is admitted or excluded under the Federal Rules of Evidence. 
Types of evidence
- ASTM E141[ Standard Practice for Acceptance of Evidence Based on the Results of Probability Sampling