Testifying at Trial

Who decides what, and under which constraints

Admissibility is the court's question. FRE 104(a) provides that “[t]he court must decide any preliminary question about whether a witness is qualified, a privilege exists, or evidence is admissible. In so deciding, the court is not bound by evidence rules, except those on privilege.” Three consequences run through the whole of an expert's trial appearance.

Admissibility is a Rule 104(a) question decided by the judge on a preponderance — which is what the December 2023 amendment wrote into the text of FRE 702 itself, requiring that “the proponent demonstrates to the court that it is more likely than not” that each of the four conditions is met.

Because the court is not bound by the rules of evidence in making that decision, the material before it can include the expert's deposition, literature that would be hearsay, and unsworn declarations — which is why the deposition transcript does so much work at the motion stage.

And FRE 104(e) is the textual home of the phrase “goes to weight”: the rule “does not limit a party's right to introduce before the jury evidence that is relevant to the weight or credibility of other evidence.” Whatever survives the Rule 104(a) ruling remains open to attack in front of the jury, and that is where Daubert's much-quoted sentence about “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof” belongs — as the response to evidence the Court described as “shaky but admissible,” not as a rule of admission.

Voir dire, and the tender the federal rules do not require

Voir dire of an expert on qualifications is conducted under FRE 104(a), with FRE 104(c) and FRE 611(a) supplying the mechanics, and it is discretionary with the court. No rule entitles an opponent to voir dire an expert before the tender.

The tender itself is a convention rather than a requirement. Nothing in the Federal Rules of Evidence requires a party to offer a witness “as an expert in” a field, and a number of federal judges discourage or forbid the practice on the ground that it invites the court to place its imprimatur on the witness in front of the jury. Describing tender as a required step misstates federal practice, whatever the local custom.

The strategic calculation is symmetrical and often resolved the same way. Voir dire in front of the jury lets an opponent establish the limits of a qualification early, but it also hands the proponent's witness a sympathetic exchange about credentials before the substance begins. Counsel defending against a qualification challenge frequently prefers to have that fight at the Rule 104 hearing and to reserve the jury version for cross-examination.

The order of proof on direct, and the reason for each step

The conventional federal sequence exists because each step forecloses something.

1. Qualification — education, training, experience, publication, prior testimony. Enough to satisfy the preamble of Rule 702 and establish credibility, not so much that it reads as a recitation.
2. The engagement — who retained the witness, when, and what the assignment was. Taken on direct because it will otherwise be taken on cross.
3. Compensation — disclosed on direct for the same reason.
4. The materials reviewed — establishes the sufficiency of facts or data under FRE 702(b) and pre-empts the examination about what was not looked at.
5. The methodology, described before the conclusion — establishes 702(c) and 702(d), and lets the reliability narrative arrive before the answer.
6. The opinions, each stated to the applicable standard of certainty and each followed by its bases.
7. The weaknesses — the contrary study, the missing data, the assumption — confronted on direct rather than left for cross.

None of it is required. FRE 705 permits the reverse order, and some counsel state the opinion first and develop the basis afterward.

On the sixth step, the 2023 Advisory Committee Note to Rule 702 is directly relevant to how an opinion should be phrased: experts “should avoid assertions of absolute or one hundred percent certainty — or to a reasonable degree of scientific certainty — if the methodology is subjective and thus potentially subject to error.” Overstatement beyond what the method supports is now an independent ground on which testimony has been limited even where the method itself survives.

Hypothetical questions after Rule 705

FRE 705 abolished the common-law requirement that an expert's opinion be preceded by a hypothetical reciting the assumed facts:

“Unless the court orders otherwise, an expert may state an opinion — and give the reasons for it — without first testifying to the underlying facts or data. But the expert may be required to disclose those facts or data on cross-examination.”

The hypothetical remains permitted and is still used, principally where the witness has no personal knowledge of the facts and the proponent wants the assumed facts stated expressly in front of the jury rather than buried in the basis. The constraint is that it must be supported by evidence in the record: a hypothetical assuming facts the jury will never hear is objectionable as assuming facts not in evidence, and an opinion resting on it is vulnerable for the same reason.

Some state systems retain more of the hypothetical-question apparatus than the federal rules do, and federal practice should not be generalized to a state courtroom without checking.

The asymmetry between Rule 703 and Rule 705

FRE 703 lets an expert base an opinion on facts or data the expert has been made aware of or personally observed, and provides that if experts in the field would reasonably rely on those kinds of facts or data, “they need not be admissible for the opinion to be admitted.” Then comes the sentence added in 2000, which is regularly stated backwards:

“But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.”

That is a reverse Rule 403 balance. Rule 403 runs in favor of admission and excludes only where prejudice substantially outweighs probative value; the last sentence of Rule 703 runs against disclosure and permits it only where probative value substantially outweighs prejudice.

Read with Rule 705, the effect is an asymmetry that is deliberate and frequently misdescribed: the cross-examiner may compel the witness to disclose the inadmissible underlying material, while the proponent may not volunteer it on the same terms. Two further limits belong with it. Rule 703 governs the type of material an expert may rely on; it does not validate a factual assumption the record contradicts. And an opinion built on assumptions the evidence does not support fails for want of a reliable application under FRE 702(d), whatever Rule 703 permits by way of source material.

What changed on 1 December 2024

Demonstratives used to be handled under the general authority of FRE 611(a). Since 1 December 2024 they have their own rule, and FRE 1006 was amended at the same time. Material written before that date — including much of the CLE material still in circulation — describes a superseded framework.

New FRE 107, Illustrative Aids, provides at (a) that the court may allow an illustrative aid “to help the trier of fact understand the evidence or argument if the aid's utility in assisting comprehension is not substantially outweighed by the danger of unfair prejudice, confusing the issues, misleading the jury, undue delay, or wasting time.” Subdivision (b) decides the deliberation room: “An illustrative aid is not evidence and must not be provided to the jury during deliberations unless: (1) all parties consent; or (2) the court, for good cause, orders otherwise.” Subdivision (c) requires an aid used at trial to be entered into the record when practicable. Rule text at the Legal Information Institute.

Amended FRE 1006(a) runs the other way: the court “may admit as evidence a summary, chart, or calculation offered to prove the content of voluminous admissible writings, recordings, or photographs that cannot be conveniently examined in court, whether or not they have been introduced into evidence.” That clause settled a recurring dispute: the underlying materials must be admissible and need not be admitted. Rule 1006(b) requires the proponent to make the originals or duplicates available to other parties, and 1006(c) sends anything functioning only as an aid to Rule 107.

Rule 611(a) has not gone anywhere. It remains the residual authority to “exercise reasonable control over the mode and order of examining witnesses and presenting evidence” — it is simply no longer the rule that governs demonstratives.

What actually goes back with the jury

The distinction is now clean enough to apply exhibit by exhibit.

• A Rule 1006 summary is evidence. It is substantive proof of the content of the underlying materials, it goes to the jury room as an exhibit, and the underlying originals or duplicates must be made available to the other parties under Rule 1006(b).
• A Rule 107 illustrative aid is not evidence. It does not go to the jury room unless all parties consent or the court orders otherwise for good cause, and it is entered into the record when practicable rather than admitted.

For an expert the consequence is concrete. A damages model presented as a chart drawn from voluminous admissible business records is a Rule 1006 exhibit and goes back. The same witness's timeline, animation or slide summarizing their own conclusions is an illustrative aid under Rule 107, is not evidence, and does not go back absent consent or good cause.

The failure mode to plan around is the hybrid: a single chart that mixes summarized record data with the expert's inferences and characterizations is neither thing cleanly. Courts have handled it by admitting the record-derived portion under Rule 1006 and treating the argumentative portion as a Rule 107 aid, or by refusing the exhibit as drawn. Building the two as separate exhibits avoids the question. Because both rules took effect only in December 2024, no settled body of application yet exists, and the safer assumption is that anything summarizing the witness's own opinions rather than record content is an aid.

Cross-examination, and the record that already exists

By the time an expert reaches the stand, most of the material for the cross-examination has been fixed for months. FRCP 32(a)(2) permits any party to use a deposition “to contradict or impeach the testimony given by the deponent as a witness,” and FRE 801(d)(1)(A) takes a prior inconsistent statement out of hearsay where the declarant testifies, is subject to cross-examination about it, and gave it under penalty of perjury at a proceeding “or in a deposition.” A deposition is named expressly, so the earlier answer comes in as substantive evidence rather than merely as impeachment.

The report is the other fixed document. An opinion the report never stated is exposed to a Rule 37(c)(1) objection, and an answer inconsistent with the report is exposed to the transcript. Between the two, the trial testimony of a well-prepared expert is largely an exercise in consistency with a record that closed at the disclosure deadline — which is why the duty in FRCP 26(e)(2) to supplement both the report and information given at deposition, running to the Rule 26(a)(3) pretrial disclosure date, is the last opportunity to correct anything.

The realistic frame is that exclusion is the exception. Most challenged experts testify, and the objectives of a challenge are more often to narrow the opinion, obtain a limiting instruction, or generate the cross-examination than to remove the witness. What remains after the Rule 104(a) ruling is a witness explaining a method to twelve people who have never seen one, with an opponent holding a transcript.

Frequently Asked Questions

Published 2026-08-12