Concept
Applying the Rule at Trial
Requirement of personal knowledge
Applying the Rule at Trial
The preceding sections treated personal knowledge as a doctrine. At trial it shows up as a handful of recurring rulings, and each one asks the same underlying question: was this witness positioned to perceive, or to deal firsthand with, the thing she is being asked about? Rule 602 sets the measure for answering it. The proponent must introduce evidence sufficient to support a finding that the witness has personal knowledge, and the witness's own testimony may supply that evidence.1 Three settings put that standard to daily use: questions that invite a guess, exhibits that must be tied to a witness who knows them, and opinions about habit.
Speculation and Conjecture
A question that asks a witness to guess what happened exceeds what she knows. A witness who lacks personal knowledge of an event cannot be asked what "probably" occurred or for her "impression" of it, and questions asking whether something "is possible," "could have been," or would have happened "if" some other fact were true draw the same objection.2 The reason is mechanical. A guess comes from reasoning, not from perception, so the jury would receive the witness's speculation dressed as testimony and would have no way to tell which parts rest on what she saw and which parts she supplied herself.
The same objection reaches opinions that float free of perception. A lay opinion that is not based on the witness's personal knowledge, or that rests on ambiguous matters, is objectionable as speculation, and the objection is sometimes phrased as calling for a conclusion.3 An expert whose basis includes so many uncertain factors that she must guess to reach a view is open to the same complaint.4 A related improper question asks one witness to say whether another witness is lying. Credibility belongs exclusively to the factfinder, and a witness's view of someone else's truthfulness adds no perception of the underlying events.5
Two witnesses to the same intersection collision show where the line falls. Suppose one watched the sedan enter the intersection and is asked how fast it was going. That question calls for her perception, and her answer, grounded in what she saw, satisfies Rule 602. Suppose the other walked up after the crash, saw only the wreckage, and is asked what the sedan driver probably did. She has no perception of the driving to report, so the question asks for a guess, and a speculation objection should be sustained. Only the witness's position relative to the event changed, and that fact moved the ruling.
Authenticating Through a Knowledgeable Witness
Exhibits raise the same question in a different form. An item is relevant only if it is what the proponent says it is, so before a contract, a weapon, or a document comes in, the proponent must produce evidence sufficient to support a finding that the item is what she claims.7 The first illustration in Rule 901(b) is testimony from a witness with knowledge that the item is what it is claimed to be, and it is among the most commonly used methods.8 Because authentication is a question of conditional relevance, the judge acts as a screen. If the proponent offers enough proof for a jury to find the item genuine, the exhibit is admitted and the jury makes the final call, while the opponent remains free to rebut.9 This is the same sufficiency standard that governs Rule 602, applied to an object instead of an event.
The standard is light, and the ax in United States v. Johnson shows how light. The victim, Papse, identified a long-handled ax seized from Johnson's home as the assault weapon, though with some hesitation. He said he was "pretty sure," that he had seen it in Johnson's hand, and that he knew it from having used it before. The Ninth Circuit held that a reasonable juror could find it was the weapon, and that Papse's inability to name distinguishing features went to weight, not admissibility.10 A witness therefore need not be certain; she must show a real connection to the item.
Chain of custody is treated the same way. In United States v. Rodriguez, DEA Agent Farley testified that he received a baggie of crack, wrapped in a newspaper subscription card bearing the defendant's name, from another agent five minutes after the transaction. He admitted that he did not watch the sale and did not know the card's exact configuration at that time. The First Circuit held that his testimony rested on personal knowledge of what he himself received, and that the defendant's complaint about the intervening five minutes was a chain-of-custody objection going to weight.11 The witness need not have seen everything that happened to the item. He must speak only to the link in the chain he personally handled.
The rule does have a floor, and United States v. Zhyltsou marks it. An agent testified that a social-media page bearing the defendant's name, photograph, and some biographical details was on the Internet at the time of trial, but he offered nothing tying the page to the defendant as its author. The Second Circuit found the authentication insufficient: the agent knew only that the page existed, and the details on it were known to others who might have created a false page.12 Compare the agent in Rodriguez. Farley knew what he had received and from whom, but the Zhyltsou agent knew only what he saw on a screen, and a sighting of the page says nothing about who made it.
Other familiar foundations follow the same logic. A witness may authenticate a photograph by testifying that it accurately portrays what she personally saw. She need not be the photographer or know anything about how the picture was taken.13 A lay witness may identify another person's handwriting if she is familiar with it from her own experience, so long as the familiarity was not acquired for the current litigation. Uncertainty in her identification usually affects weight, though an opinion can become so conclusory that it fails the sufficiency standard.14
Habit and Routine Practice
Testimony that a person or an organization has a habit or routine practice also depends on the witness's own observation. Rules 602 and 701 together make a nonexpert's opinion admissible when it rests on personal knowledge and helps the trier of fact, so a coworker who has watched a clerk handle outgoing mail every day may give an opinion about the clerk's routine.16 When the habit is contested, the court may require the witness to disclose the specific instances behind her opinion, and the opponent may probe them on cross-examination. Specific instances offered to prove a habit remain subject to Rule 403, so a judge may admit one witness's account of many occasions and exclude ten witnesses describing one occasion each.17 A person who has never seen the routine has nothing to base the opinion on, and her testimony falls to a personal-knowledge objection.
Speculation and Conjecture
Rule 602 lets a witness testify only to matters she has personal knowledge of, so a question that asks her to guess is a question about something she does not know.19 The objection is called speculation or conjecture, and it applies whenever the witness lacks personal knowledge of the event and is asked to surmise what occurred. A question asking what "probably" happened, or for the witness's "impression" of an event she did not perceive, draws it. So do questions asking whether something "is possible" or "could have been" true, and "what if" questions that ask her to reason from a hypothetical.20
The reason for the objection lies in how testimony earns its value. Cross-examination can test a witness's eyesight, her vantage point, and her memory, but it has nothing to test when the answer comes from no perception at all. A guess also arrives in the same voice as real testimony, so the jury cannot tell which parts of an answer rest on what the witness saw and which parts she supplied herself. The rule therefore keeps out material that adds noise to the record without adding evidence.
The same objection reaches several questions that do not look like guesses at first. A lay opinion that is not based on the witness's personal knowledge, or that rests on ambiguous matters, is objectionable as speculation, and the objection is sometimes confusingly phrased as calling for a conclusion. An expert faces the same problem if her opinion depends on so many varying or uncertain factors that she must guess to reach it.21 A question asking one witness to comment on whether another witness is telling the truth is also improper, because credibility belongs exclusively to the factfinder and the commenting witness has perceived nothing about the underlying events that the jury has not. A cross-examiner who asks "Are you saying Mr. Jones is a liar?" will be stopped, although some trial courts allow the milder form, "Do you disagree with Mr. X, who testified that...?"22
A classroom problem about a witness named Wyn shows how a court sorts proper inferences from improper ones. Suppose Wyn was jogging when an SUV approached from the opposite direction, and she is asked three questions. Her opinion that a screeching sound came from someone braking a vehicle was properly allowed, because she had experience with that sound and the opinion rested on her own hearing. Her opinion that the sound came from the SUV was properly excluded, because she did not say she saw the vehicle as it made the noise. Without that perception, her connection of the sound to the SUV was a surmise, which also shows that Rule 602 and the lay-opinion rule can reach the same result.23 Her estimate of the SUV's exact speed was the close call. She was running in the opposite direction and had no reference speed of her own, so the court allowed only a range: faster than 25 and 40 miles per hour, but not faster than 60.24 Limiting her to the range matched the testimony to what her perception could support.
A second pair of facts makes the contrast sharper. A bystander who watched a collision may answer open questions about what she saw, because every answer comes from her perception. If she is then asked what would have happened had the light been green, the question requires her to build a scenario she never observed, and a speculation objection should be sustained. The witness and the event are the same in both questions. What changed is whether the answer depends on perception or on invention.
Authenticating Through a Knowledgeable Witness
Exhibits raise the personal-knowledge question in a different form. A witness's account of an event is useful only if she perceived the event, and an exhibit is useful only if it is the thing the proponent says it is. Authentication is therefore a refinement of relevance: a weapon, a letter, or a package of drugs proves nothing unless it really connects to the people and events in the case. Rule 901(a) asks the proponent for evidence sufficient to support a finding that the item is what she claims.26 The most common way to meet that standard is the first illustration in Rule 901(b), testimony from a witness with knowledge that the item is what it is claimed to be. Such a witness supplies the missing link between the object and the case, and the opponent can test that link on cross-examination.27
The standard asks for a real connection, not certainty, and United States v. Johnson shows how modest the demand is. Johnson was prosecuted for an ax attack on a man named Papse, and officers seized a long-handled ax at Johnson's home five days later. Papse identified it as the weapon, apparently with hesitation, saying he was "pretty sure," that he had seen it in Johnson's hand, and that he knew it from having used it before. Johnson objected that Papse could not name features distinguishing this ax from any other, and that he seemed to assume it was the weapon because it was the only ax on the premises. The Ninth Circuit held that a reasonable juror could find this was the weapon, so the foundation was adequate. The witness's inability to point to distinguishing marks, and any change in the ax's condition, went to the weight the jury should give the identification.28 The reason for that allocation is that the judge only screens for a prima facie showing. Once it is made, credibility and probative force belong to the jury.
Chain-of-custody testimony works the same way, because each witness in the chain vouches only for the link she personally handled. In United States v. Rodriguez, a controlled buy of crack produced a baggie wrapped in a Boston Globe subscription card bearing the defendant Famania's name and address. DEA Agent Farley testified that he received the package from another agent within five minutes of the transaction and that it was in the same condition when it reached the courtroom. On cross-examination he conceded that he had not watched the sale, had not seen the card when it was picked up, and did not know its exact configuration at that moment. The First Circuit held that Farley's testimony rested on personal knowledge of what he himself received, and it treated the objection about the unobserved five minutes as a chain-of-custody complaint, not a Rule 602 problem.29 Farley did not need to have seen everything that happened to the card. He needed only to know what came into his own hands, and the earlier links were supplied by other witnesses.
The contrast with a case that fails shows which fact carries the result. In United States v. Zhyltsou, a federal agent testified that a social-media page bearing the defendant's name, photograph, and some biographical details was accessible on the Internet at the time of trial. The government conceded that the agent did not know who created the page, yet it argued to the jury that the defendant had written it. The court held that the foundation was insufficient. Nothing connected the page to the defendant as its author, and every detail on it was also known to others, some of whom might have wanted to create a false page in his name.30 Farley could say what he received and from whom, which linked the card to the transaction. The Zhyltsou agent could say only what appeared on a screen, which showed that the page existed but nothing about where it came from. A witness who has handled or perceived the thing in the relevant connection supplies a link, while one who merely sees it at trial time supplies none.
Two other familiar foundations rest on the same idea of knowledge acquired firsthand. A photograph used to illustrate testimony is authenticated when a witness who personally observed the scene says the photograph accurately portrays it. The witness need not be the photographer or know anything about when or how the picture was taken, because her personal knowledge of the scene is what makes her able to verify it. The photograph remains subject to Rule 403, so a misleading image may still be excluded.31 Handwriting is similar. A layperson who is familiar with another person's handwriting, such as a spouse, may testify that the writing on a document is that person's. An expert may also make the identification by comparing the document with authenticated samples.32 A witness who actually saw someone write or sign a document, or who saw another connection such as finding or possessing it, can likewise authenticate it from her own perception.33 In each setting the question is whether this witness has a genuine connection to the item, not whether she knows everything about it.