Competent evidence is information a court will actually let a jury consider: it has to be relevant to a fact that matters, come from a qualified source, be properly authenticated, and avoid any rule — hearsay, privilege, constitutional violation, improper character use — that would keep it out. Clearing one of those hurdles isn’t enough. A signed confession is useless if police obtained it unlawfully. A damning text message means nothing if no one can prove who wrote it. A relevant eyewitness account can still be excluded if the witness has no personal knowledge of what they’re describing. Competency is the sum of several filters, and evidence has to pass all of them.
Relevance Comes First
Under Federal Rule of Evidence 401, evidence is relevant if it makes a fact of consequence more or less probable than it would be without the evidence.1Legal Information Institute. Federal Rules of Evidence Rule 401 – Test for Relevant Evidence In a theft case, fingerprints on the stolen item clear that bar easily. Testimony about the defendant’s favorite restaurant does not.
Relevance alone doesn’t guarantee admission. Rule 403 lets a judge exclude relevant evidence when the risk of unfair prejudice, jury confusion, or wasted time substantially outweighs its usefulness.2United States District Court Northern District of Illinois. Federal Rules of Evidence Rule 403 – Exclusion of Relevant Evidence Graphic crime-scene photographs are the classic example. One clear photo of a wound might come in; twenty from different angles can be excluded as needlessly inflammatory. The word “substantially” tilts the rule toward admission: prejudice has to clearly outweigh probative value before a judge keeps the evidence out.
Who Can Testify
Every person is presumed competent to take the stand unless a specific rule says otherwise.3Legal Information Institute. Federal Rules of Evidence Rule 601 – Competency to Testify in General Courts don’t require witnesses to pass a mental aptitude test or prove their moral character. Memory, bias, and intelligence go to how much weight the jury gives the testimony, not to whether the witness can testify at all.
Two concrete requirements still apply. A witness must have personal knowledge of the subject — they need to have seen, heard, or otherwise experienced what they’re describing, and there must be enough evidence to support that claim.4GovInfo. Federal Rules of Evidence – Rule 601 and Rule 602 A coworker who heard about an accident secondhand can’t take the stand to describe it. And every witness must take an oath or affirmation to tell the truth before saying a word.
When a young child or a person with a cognitive impairment is called, a judge can hold a brief preliminary inquiry into whether the witness understands the duty to be truthful and can describe events coherently. In civil cases where state law supplies the governing rule, state competency standards can override the federal default.
Rules That Block Otherwise Relevant Evidence
Several rules keep relevant evidence away from the jury because the law considers it unreliable, unfair, or constitutionally tainted.
Hearsay
Hearsay is an out-of-court statement offered at trial to prove the truth of what the statement asserts.5Legal Information Institute. Federal Rules of Evidence Rule 801 – Definitions That Apply to This Article; Exclusions from Hearsay If a witness says, “My neighbor told me the defendant ran the red light,” that’s hearsay. The neighbor isn’t in the courtroom, wasn’t under oath, and can’t be cross-examined. Hearsay is inadmissible unless a recognized exception applies.6Legal Information Institute. Federal Rules of Evidence Rule 802 – The Rule Against Hearsay
Privileged Communications
Attorney-client conversations, spousal communications, and discussions between a patient and their doctor are shielded from disclosure at trial. Even when a privileged conversation contains information directly relevant to the case, a person generally can’t be forced to reveal it. The rationale is practical: people need to speak honestly with their lawyers and doctors, and they won’t if those conversations can be dragged into court.
The Exclusionary Rule
When law enforcement obtains evidence by violating a person’s constitutional rights, the exclusionary rule keeps that evidence out.7Constitution Annotated. Amdt4.7.1 Exclusionary Rule and Evidence The most common scenario involves Fourth Amendment violations: anything discovered during an unreasonable search can be suppressed. The principle also reaches coerced confessions under the Fifth Amendment and evidence gathered when the government violated a defendant’s Sixth Amendment right to counsel.
Character Evidence
Evidence about a person’s general character or past behavior usually can’t be used to argue they acted the same way on the occasion in question.8Legal Information Institute. Federal Rules of Evidence Rule 404 – Character Evidence; Other Crimes, Wrongs, or Acts A defendant’s history of bar fights can’t be introduced to suggest they started this one. Narrow exceptions exist: a criminal defendant can present evidence of their own good character, and past acts are sometimes allowed to show motive, intent, preparation, or a common plan. The default, though, is exclusion. The concern is that juries who hear about past bad acts will convict on character rather than on the evidence specific to the case.
When Hearsay Is Still Allowed
The hearsay rule has dozens of exceptions, each built around circumstances the law considers inherently trustworthy. The workhorses under Rule 803 apply whether or not the person who made the original statement is available to testify:9Legal Information Institute. Federal Rules of Evidence Rule 803 – Exceptions to the Rule Against Hearsay
- Present sense impression: a statement describing an event made while the person was watching it happen, or immediately after. The theory is that there’s no time to fabricate.
- Excited utterance: a statement made while the person was still under the stress of a startling event.
- Statements for medical treatment: a patient’s description of symptoms or how an injury happened, given to a doctor for treatment purposes. Patients have a strong incentive to be accurate when their health depends on it.
- Business records: records made in the regular course of business, at or near the time of the event, by someone with knowledge. A hospital’s admission log or a company’s shipping records qualify.
- Public records: official records, reports, and data compilations from government agencies.
A separate set of exceptions under Rule 804 covers statements where the person is unavailable, but these Rule 803 exceptions appear in trials constantly.
Authenticating Physical and Digital Evidence
Before any item goes to the jury, the party offering it must prove it’s genuinely what they claim it is. Rule 901 applies to everything from a signed contract to a text message to a weapon: the proponent must present enough evidence to support a finding that the item is what it purports to be.10Legal Information Institute. Federal Rules of Evidence Rule 901 – Authenticating or Identifying Evidence
Common authentication methods include testimony from someone who recognizes the item, handwriting comparison by a familiar person or an expert, and distinctive characteristics like the document’s appearance or internal content. For physical evidence such as drugs or weapons, authentication often turns on chain of custody: each person who handled the item testifies about receiving it, what they did with it, and whom they gave it to. Unexplained gaps give the opposing side ammunition to argue the item may have been tampered with or swapped.
Digital evidence raises its own challenges. Emails can be authenticated through testimony from someone who saw them sent or received, or through distinctive characteristics like the sender’s known email address and writing style. Text messages and social media posts follow the same approach, with courts accepting circumstantial evidence such as the author’s phone number, screen name, references to facts only that person would know, and consistent writing habits. Printing a screenshot and offering it without supporting testimony almost never works.
A related rule, often called the best evidence rule, requires that when you’re trying to prove the contents of a document, recording, or photograph, you must produce the original rather than a summary or someone’s memory of what it said.11Legal Information Institute. Federal Rules of Evidence Rule 1002 – Requirement of the Original If a contract’s specific language matters, the contract needs to be introduced, not a witness saying “I remember it said something about a penalty clause.”
Expert Witnesses and the Daubert Standard
Ordinary witnesses can only describe what they personally observed. Experts can offer opinions based on specialized knowledge, but they have to meet a higher reliability bar. Under Rule 702, expert testimony is admissible only when the proponent shows it is more likely than not that the expert’s knowledge will help the jury, the testimony rests on sufficient facts, and the expert applied reliable methods correctly to the case at hand.12Legal Information Institute. Federal Rules of Evidence Rule 702 – Testimony by Expert Witnesses
Since the Supreme Court’s 1993 decision in Daubert v. Merrell Dow Pharmaceuticals, federal judges serve as gatekeepers who evaluate the reliability of expert testimony before it reaches the jury.13National Institute of Justice. Daubert and Kumho Decisions The Daubert factors include:
- Whether the expert’s theory or technique can be tested and has been tested
- Whether it has been subjected to peer review and publication
- Its known or potential error rate
- Whether standards exist for controlling the technique’s application
- Whether the method has gained general acceptance in the relevant scientific community
These factors aren’t a rigid checklist, and a judge has broad discretion to weigh them based on the type of expertise involved. Speculation won’t pass. If an expert’s opinion amounts to a guess rather than a conclusion drawn from a tested methodology, the testimony gets excluded. This is where a lot of junk science gets filtered out.
How Competency Gets Fought Over
The judge decides all preliminary questions about whether evidence is admissible, whether a witness is qualified, and whether a privilege applies.14Legal Information Institute. Federal Rules of Evidence Rule 104 – Preliminary Questions On these calls the judge isn’t bound by the normal evidence rules (except privilege rules), so the judge can consider information that wouldn’t itself be admissible to decide whether other evidence gets in.
Motions in Limine
The most strategic evidence fights happen before trial. A motion in limine asks the judge to rule in advance that certain evidence is inadmissible, so the jury never hears something that shouldn’t have been mentioned. A plaintiff’s attorney might file one to keep out evidence of an unrelated criminal history; a defense attorney might seek to exclude a coerced confession. Winning a motion in limine can reshape the entire trial.
Objections During Trial
When problematic evidence comes up unexpectedly during testimony, the attorney’s tool is the objection. To preserve the issue for appeal, the objection must be timely and state the specific ground, such as “hearsay” or “lack of foundation.”15Office of the Law Revision Counsel. Federal Rules of Evidence Rule 103 – Rulings on Evidence The judge rules immediately. If a judge excludes evidence and the offering attorney believes that’s wrong, the attorney must make an offer of proof explaining what the evidence would have shown, so an appellate court can later assess whether the exclusion mattered.
Appellate Review
Trial judges get significant leeway on evidence calls. Appellate courts review these rulings under an abuse of discretion standard, meaning the appeals court won’t overturn the decision unless the trial judge’s ruling was clearly unreasonable, and even then the error must have affected a substantial right of the losing party. Most evidence rulings survive on appeal, which is why pretrial motions and well-timed objections carry so much weight.