Is The Worst Rule of Evidence Finally Doomed?
Longtime readers of this blog will detect a certain skepticism concerning the Federal Rules of Evidence, particularly when it comes to things like character evidence rules, excited utterances, and whether and under what circumstances routine corporate e-mail should be admissible. We are hardly alone in this position. Judge Posner notably suggested eliminating most hearsay exceptions for “having neither a theoretical nor an empirical basis,” and being a form of “folk psychology” that was “not even common sense” and “rests on no firmer ground than judicial habit.” [1]
Not all evidence rules are bad, but bad rules of evidence often share some common traits. Usually they're old, as the modern Rules Committee tends to think things through more carefully and solicit public comment more broadly than was expected or even possible in the 1970s. And like lots of bad law, bad rules of evidence are not so much malicious as they are underbaked. A tried and true recipe for bad law of all kinds is to make an exception to an existing rule based upon a vague and not terribly principled distinction and then codify it without thinking through the broader implications. For example, the common law recognized a distinction between an action for “trespass” and an action for “trespass on the case” that appears meaningless to modern eyes but could doom a litigant's claims under English law for centuries. This legal wrangling around forms of trespass seems primitive today, but it's also easy to imagine a lawyer in 2126 saying the same thing about the pools of ink spilled over whether a shareholder's claim is “direct” or “derivative” under Delaware law.
The Advisory Committee on Evidence Rules recently met to discuss changes to the Federal Rules of Evidence. And at long last they proposed a change to what has been called the “worst rule of evidence,” an underbaked rule which legal scholars have been roundly criticizing for the better part of 40 years.
The rule in question is Rule 104(b). In its current form it reads as follows:
(b) Relevance That Depends on a Fact. When the relevance of evidence depends on whether a fact exists, proof must be introduced sufficient to support a finding that the fact does exist. The court may admit the proposed evidence on the condition that the proof be introduced later.
The commentary explains the purpose behind the rule and introduces the concept of “conditional relevancy” through a few examples.
Subdivision (b). In some situations, the relevancy of an item of evidence, in the large sense, depends upon the existence of a particular preliminary fact. Thus when a spoken statement is relied upon to prove notice to X, it is without probative value unless X heard it. Or if a letter purporting to be from Y is relied upon to establish an admission by him, it has no probative value unless Y wrote or authorized it. Relevance in this sense has been labelled “conditional relevancy.” Morgan, Basic Problems of Evidence 45–46 (1962). Problems arising in connection with it are to be distinguished from problems of logical relevancy, e.g. evidence in a murder case that accused on the day before purchased a weapon of the kind used in the killing, treated in Rule 401.
At first blush, this doesn't seem so crazy. If a piece of evidence is only relevant if some fact is true, then it probably isn't worth introducing if the fact is obviously false. And the judge decides all other questions of admissibility, so why not this one? But like many bad legal rules, the more you think about it, the less sense it makes. The logic underlying the rule of “conditional relevancy” has all the strength of cotton candy.
Let's start by defining the set of evidence that this rule is meant to apply to. By its terms, that would be evidence that is only relevant if a particular fact exists. As Professor Vaughn Ball pointed out back in 1980, that's literally all evidence. [2] Imagine the most obviously relevant piece of evidence that you can—say the gun used in an armed robbery case. That gun is only relevant if:
1) there was a victim to rob,
2) the victim possessed money or property,
3) The defendant had possession of the gun,
4) the defendant acquired the money or property from the victim, and
5) the exchange wasn't voluntary.
If any of those “conditional facts” are false, there isn't any relevance to the gun and it shouldn't be offered into evidence. In fact as a dangerous weapon, introducing the gun would be deeply prejudicial. Anyone with half a brain could repeat this exercise for literally any exhibit in any case.
But as dumb as that exercise would be, Rule 104(b) itself is actually so much dumber than that. I jotted down five facts to make a point, but that's an arbitrary number. In truth, the number of facts that are prerequisite to relevancy is effectively boundless. Every other element of the claim or crime at issue is a prerequisite, but so are countless factual inquiries, such as whether the relevant statute was properly passed into law, whether the various portions of the charging party's story are true, and various unknowable mental states and impressions.
OK, so the set of evidence that 104(b) applies to is “everything” and the number of facts to be evaluated is boundless. What about the standard that the court uses to evaluate those facts? This is also a total mess. Normal relevance determinations under Rule 401 are evaluated under a preponderance of the evidence standard. [3] But Rule 104(b) has a different, lower, “evidence sufficient to support a finding that the fact does exist” standard. In addition, the court can admit the evidence on the condition that the proof be introduced later.
Ah, but it gets worse. In the same way that every possible piece of evidence can generate an unbounded list of 104(b) facts to evaluate, any normal relevance question can be converted into a conditional relevance inquiry. All you have to do is come up with a set of “conditional facts” that, if true, would make the evidence unambiguously relevant. And analytically those facts aren't really any different than the ones that you would use in a conventional argument to admit an exhibit.
For example, imagine that you're arguing that an e-mail is relevant. You could claim that it's evidence of a conspiracy between the parties to the message. But you could also just assert that the parties were in a conspiracy and that the communications made by the conspirators are thereby clearly relevant. It's basically the same argument, in fact almost all of the words are the same, but the burden of proof under Rule 104(b) would theoretically be lower. Indeed, the 10th Circuit observed just last year that “[a] savvy lawyer can potentially turn any question of Rule 401 relevance into a Rule 104(b) conditional question.” [4]
Commentators have suggested reforming or scrapping Rule 104(b) for decades. But at the Rules Advisory Committee meeting this May, a proposal came out that would finally do something about the issue. The minutes of the meeting are an interesting read. They include the chair recognizing that Rule 104(b) has been called the “worst rule of evidence” and taking commentary from Professor Allen, who suggested fixing the rule in an article published back in 1992. [5] Based upon that meeting, the Advisory Committee proposed a revised Rule 104(b) which is currently out for comment. It reads as follows:
(b) Relevance. To establish that evidence is relevant, the proponent must demonstrate to the court that the trier of fact could reasonably find that the requirements of Rule 401 have been met. In making its relevance determination, the court may consider the evidence itself, other evidence, and common knowledge and experience. The court may admit the proposed evidence on the condition that the further proof be introduced later.
This revised rule at long last murders the notion of “conditional relevance.” As a result, it largely collapses Rule 104(b) into Rule 401. The court is instructed to admit evidence if the proponent convinces the court by a preponderance of the evidence that the jury could find it relevant under Rule 401. And it gives the court discretion to allow the evidence in provisionally with the proof taken later.
It typically takes about three years for proposed evidence rule changes to go into effect. If approved by the Supreme Court and Congress, this change would not be implemented until January of 2029, just shy of 50 years after Professor Bell's original article pointing out the conditional relevance is a logically incoherent concept.
Judicial habits, even bad ones, die hard.
[1] United States v. Boyce, 742 F.3d 792, 802 (7th Cir. 2014) (Posner, J concurring).
[2] Vaughn C. Ball, The Myth of Conditional Relevancy, 14 GA. L. REV. 435 (1980).
[3] See Bourjaily v. United States, 483 U.S. 171 (1987).
[4] United States v. Paycer, 154 F.4th 1261, 1288 (10th Cir. 2025).
[5] Ronald J. Allen, The Myth of Conditional Relevancy, 25 Loy. L.A. L. Rev. 871 (1992).
