Black-letter propositions
- 01
Qualification can rest on knowledge, skill, experience, training, or education.
- 02
Gatekeeping considers testing, peer review, error rate, standards, acceptance, fit, and discipline-specific indicators.
- 03
Experts may rely on personally known, admitted, or field-reasonable facts; otherwise inadmissible bases are disclosed to the jury only when value substantially outweighs prejudice.
- 04
Experts may address ultimate issues, but a criminal expert generally cannot state whether the defendant had the mental state constituting an element or defense.
- 05
A learned treatise can be read into evidence through a qualified foundation but is not ordinarily received as an exhibit.
Use this attack sequence under time
Frame the issue
Define specialized issue and helpfulness.
Resolve the next checkpoint
Qualify witness.
Resolve the next checkpoint
Identify data, method, and application.
Resolve the next checkpoint
Analyze reliability and fit.
Finish the conclusion
Check basis disclosure and ultimate-issue limits.
Common wrong turns
- Credentials alone do not establish reliability.
- An expert cannot simply relay inadmissible accusations.
- A legal conclusion telling the jury what law controls may be unhelpful.
Worked example
An engineer uses an untested litigation-only method and cannot explain error rate or application.
The court may exclude the opinion for lack of demonstrated reliability and fit despite strong credentials.
Practice this topic
Rule 702 and what the proponent must show
Rule 702 lets a witness qualified as an expert by knowledge, skill, experience, training or education testify in the form of an opinion if the proponent demonstrates that it is more likely than not that four things are true. The expert's specialized knowledge will help the trier of fact. The testimony is based on sufficient facts or data. It is the product of reliable principles and methods. And the opinion reflects a reliable application of those principles and methods to the facts.
The burden and standard are stated in the rule: the proponent must show it is more likely than not.
Bases, ultimate issues and disclosure
Rule 703 lets an expert base an opinion on facts or data the expert was made aware of or personally observed, and if experts in the field would reasonably rely on them, they need not be admissible. Inadmissible facts may be disclosed to the jury only if their probative value in helping evaluate the opinion substantially outweighs their prejudicial effect. Rule 704 says an opinion is not objectionable just because it embraces an ultimate issue, but in a criminal case an expert must not state an opinion about the defendant's mental state that is an element of the crime or defense.
Rule 705 lets an expert state an opinion and reasons without first testifying to underlying facts, though cross-examination may require disclosure. Rule 706 lets the court appoint experts.
Frequently asked questions
What is the controlling rule for qualification, reliability, bases, and scope?+
Expert evidence requires qualification, reliable methodology and application, sufficient data, and a helpful fit to the disputed issue.
How should I analyze qualification, reliability, bases, and scope on the bar exam?+
Define specialized issue and helpfulness. Qualify witness. Identify data, method, and application. Analyze reliability and fit. Check basis disclosure and ultimate-issue limits.
What must a proponent show under Rule 702?+
That it is more likely than not that the expert's knowledge will help the trier of fact, the testimony rests on sufficient facts or data, uses reliable methods and reliably applies them to the case.
Can an expert rely on inadmissible facts?+
Yes, if experts in the field would reasonably rely on them, under Rule 703, but the jury hears them only if probative value substantially outweighs prejudicial effect.
Can an expert give an opinion on an ultimate issue?+
Generally yes. Rule 704(a) says an opinion is not objectionable just because it embraces an ultimate issue, with a criminal mental-state exception in Rule 704(b).
What is the criminal mental-state exception?+
Rule 704(b) says an expert must not state an opinion about whether the defendant did or did not have a mental state or condition that is an element of the crime or a defense.
Does an expert have to state the underlying facts first?+
No. Rule 705 lets the expert state an opinion and reasons without first testifying to the underlying facts, though the expert may be required to disclose them on cross-examination.