Evidence in courts is not ruled “invalid” but rather “inadmissible.” For evidence to be admitted in a court of law, it must meet four fundamental tests:
- It must be proven to be authentic, meaning that it is actually what the party presenting it claims it to be;
- It must be relevant, meaning that it’s admission would have some effect on a matter of material fact in dispute;
- It must not be more prejudicial than probative, meaning that it is not likely to have a more emotional impact on the finder of fact than a logical impact; and
- It must not be otherwise objectionable under any of the existing rules of evidence in the jurisdiction (such as hearsay).
Thus, something can be ruled inadmissible if it cannot be proven by the party who wishes to present it to be authentic, it is not relevant to a matter in dispute before the court, it is intended to unreasonably inflame the emotions of the finder of fact, or it is objectionable under some statute or court rule.
Examples of each might be:
Authenticity:
You claim to have a contract that was signed by the opposing party, but there are no witnesses and the opposing party disputes ever signing it. Likely to be inadmissible because you cannot prove that the contract is what you claim it to be.
Relevance:
You want to admit evidence that a defendant cheated on their spouse in a matter related to a commercial contractual breach. Cheating isn’t illegal, and has no bearing on the contractual relationship in a commercial setting.
Prejudice:
You want to admit detailed and gory photographs of injuries sustained by your client when you have sufficient other evidence to prove the amount of damage inflicted (medical records, eyewitnesses, doctors who provided treatment, etc).
Likely inadmissible as the photographs aren’t needed to prove the point, but will likely inflame the emotions of the Court.
Statutory/Rule Exception:
You want to bring your opposing party’s Advocate to the stand to testify about what their client told them in preparing for the case. This is inadmissible as a violation of the Advocate-client privilege, protected by both court rules and/or statute.