Rules of evidence in the context of "Witness"

A trial court or court of first instance is a court having original jurisdiction, in which trials take place. Appeals from the decisions of trial courts are usually heard by higher courts with the power of appellate review (appellate courts). Most appellate courts do not have the authority to hear testimony or take evidence, but instead rule solely on matters of law.

In the trial court, evidence and testimony are admitted under the rules of evidence established by applicable procedural law and determinations called findings of fact are made based on the evidence. The court, presided over by one or more judges, makes findings of law based upon the applicable law. In most common law jurisdictions, the trial court often sits with a jury and one judge; in such jury trials, the jury acts as trier of fact. In some cases, the judge or judges act as triers of both fact and law, by either statute, custom, or agreement of the parties; this is referred to as a bench trial.

An ex post facto law is a law that retrospectively changes the legal consequences or status of actions that were committed, or relationships that existed, before the enactment of the law. In criminal law, it may criminalize actions that were legal when committed; it may aggravate a crime by bringing it into a more severe category than it was in when it was committed; it may change the punishment prescribed for a crime, as by adding new penalties or extending sentences; it may extend the statute of limitations; or it may alter the rules of evidence in order to make conviction for a crime likelier than it would have been when the deed was committed.

Conversely, a form of ex post facto law called an amnesty law may decriminalize certain acts. Alternatively, rather than redefining the relevant acts as non-criminal, it may simply prohibit prosecution; or it may enact that there is to be no punishment, but leave the underlying conviction technically unaltered. A pardon has a similar effect, except it applies in just one case instead of a class of cases. Other legal changes may alleviate possible punishments retroactively, for example by replacing the death sentence with lifelong imprisonment. Such legal changes are also known by the Latin term in mitius.

Relevance, in the common law of evidence, is the tendency of a given item of evidence to prove or disprove one of the legal elements of the case, or to have probative value to make one of the elements of the case likelier or not. Probative is a term used in law to signify "tending to prove". Probative evidence "seeks the truth". Generally in law, evidence that is not probative (doesn't tend to prove the proposition for which it is proffered) is inadmissible and the rules of evidence permit it to be excluded from a proceeding or stricken from the record "if objected to by opposing counsel". A balancing test may come into the picture if the value of the evidence needs to be weighed versus its prejudicial nature.

A court of record is a trial court or appellate court in which a record of the proceedings is captured and preserved, for the possibility of appeal. A court clerk or a court reporter takes down a record of oral proceedings. That written record (and all other evidence) is preserved at least long enough for all appeals to be exhausted, or for some further period of time provided by law (for example, in some U.S. states, death penalty statutes provide that all evidence must be preserved for an extended period of time).

Most courts of record have rules of procedure (see rules of evidence, rules of civil procedure, and rules of criminal procedure) and therefore they require that most parties be represented by counsel (specifically, attorneys holding a license to practice law before the specific tribunal).