Module 1: Relevance, Character Evidence & Other Bad Acts

Rule 401 sets a deliberately low bar: evidence is relevant if it has any tendency to make a fact of consequence more or less probable. Rule 402 provides that relevant evidence is generally admissible unless a specific rule says otherwise, and irrelevant evidence is never admissible.

The deliberately low bar exists because relevance was never meant to be the rule that does the real filtering work — it’s designed to admit almost everything that could plausibly matter, leaving the harder judgment calls to more specific rules like Rule 403 and the character evidence provisions that follow. Courts often describe relevant evidence as just one “brick in the wall” of a party’s case — a single piece of circumstantial evidence rarely proves anything by itself, and Rule 401 doesn’t require it to. It’s enough that the evidence shifts the probability of a fact of consequence even slightly, which is why courts admit a genuinely wide range of circumstantial evidence — a defendant’s flight from the scene, a motive established years earlier, even an odd coincidence in timing — each one, alone, inconclusive, but each one clearing Rule 401’s low threshold on its own.

Example. In a car accident case, evidence that the defendant was texting moments before the crash has real tendency to make careless driving more probable — relevant, even though it doesn’t conclusively prove anything on its own. Now compare: evidence about the defendant’s taste in music has no logical tendency to make any fact of consequence more or less probable — irrelevant, and therefore inadmissible under Rule 402 regardless of anything else.

Even relevant evidence can be excluded if its probative value is substantially outweighed by a danger of unfair prejudice, confusion, misleading the jury, undue delay, wasted time, or needless cumulative evidence — a genuinely demanding standard favoring admission.

Old Chief v. United States, 519 U.S. 172 (1997), shows Rule 403 doing real, decisive work. A defendant charged with being a felon in possession of a firearm offered to stipulate that he had a prior qualifying felony conviction — satisfying that element of the crime without the jury ever learning what the underlying conviction was for. The prosecution refused the stipulation and insisted on introducing the full record of his prior conviction, which happened to be for assault causing serious bodily injury, arguing prosecutors generally have the right to present their case with the evidence of their choosing rather than accept a defendant’s substitute. The Supreme Court held that where a stipulation offers essentially identical probative value on a purely formal, status-type element like “prior felony conviction,” while the full record adds real, unfair prejudice by inviting the jury to think of the defendant as a violent person generally, the district court abused its discretion in rejecting the stipulation. The case is the leading authority for weighing a party’s marginal probative gain from more detailed evidence against the real prejudice that detail can add — not just whether the underlying fact is relevant at all.

Example. Graphic autopsy photos with only marginal additional probative value (the cause of death is already undisputed) risk exclusion under Rule 403, given their serious potential to inflame the jury emotionally. Now compare: those same photos, offered to prove a genuinely disputed and important fact (like the exact manner of death), would likely survive Rule 403, since their real probative value is much higher.

Rule 404(a) bars using a person’s character (or a character-suggesting act) to prove they acted in conformity with that character on a particular occasion — the “propensity” prohibition, applying even to genuinely true character evidence.

People v. Zackowitz, 254 N.Y. 192 (1930), Judge Cardozo’s opinion for the New York Court of Appeals, remains one of the clearest illustrations of why the propensity ban applies even to evidence that’s completely true and genuinely unsettling. A man shot and killed another man after a heated confrontation; at trial, the prosecution introduced evidence that the defendant owned a small arsenal of firearms at home, none of which were the actual murder weapon, arguing this showed he was the kind of violent person who would commit murder. Cardozo reversed the conviction, holding that evidence of the defendant’s weapon collection was inadmissible precisely because its only real relevance was to suggest a violent disposition and invite the jury to convict based on the defendant’s general character rather than what he actually did on the night in question. The opinion is still cited for its blunt articulation of the underlying policy: the law is not concerned with punishing sinful thoughts or violent tendencies in the abstract, only with proving the specific act charged, and true, damaging character evidence is exactly the kind of proof most likely to distract a jury from that narrower question.

Example. A prosecutor argues Peter’s prior theft conviction shows he’s “the type of person” who steals, so he probably committed this theft too — inadmissible pure propensity reasoning, regardless of how true the prior conviction is.

A criminal defendant may offer their own pertinent good character, opening the door to prosecution rebuttal. In cases like self-defense, the alleged victim’s character for violence can be relevant. A witness’s character for truthfulness is a separately recognized area (Rule 608).

Michelson v. United States, 335 U.S. 469 (1948), remains the leading case on exactly how far the door swings open once a defendant chooses to offer their own good character. A man charged with bribing a federal agent called witnesses to testify to his reputation for honesty and being a law-abiding citizen; on cross-examination, the prosecution asked one of those witnesses whether he had heard that the defendant had been arrested, decades earlier, for receiving stolen goods — a prior arrest, not even a conviction, that would otherwise have been wholly inadmissible. The Supreme Court upheld the question, explaining that a defendant who voluntarily puts his own character in issue accepts the real risk that the prosecution may test the genuineness of the reputation testimony by asking whether the witness had heard of specific instances inconsistent with it — the question wasn’t offered to prove the defendant actually committed the earlier offense, only to probe whether the witness’s rosy account of his reputation was honestly informed. Justice Jackson’s opinion candidly acknowledged the rule is something of an anomaly, tolerated because a defendant who opens this particular door has chosen to gamble on his own good name.

Example. A defendant claiming self-defense introduces evidence of the alleged victim’s reputation for violence, relevant to who was likely the first aggressor — a recognized exception. Now compare: that same defendant also offers evidence of their own reputation for peacefulness — proactively opening the door, letting the prosecution respond with contrary character evidence if it has any.

When character evidence is admissible, reputation and opinion testimony are the standard, more freely available methods. Specific instances of conduct are more restricted — generally limited to cross-examination, or situations where character is itself an essential element of a claim or defense.

The reason specific instances are treated so much more cautiously than reputation and opinion testimony comes down to real, practical trial-management concerns, not just formalism. Reputation and opinion testimony can be delivered quickly, tested through ordinary cross-examination, and don’t require the jury to resolve a genuine factual dispute about whether some earlier, collateral incident actually happened. Specific instances, by contrast, risk turning a trial into a series of mini-trials about unrelated past events — each one contested, each one requiring its own witnesses and proof — consuming time on issues genuinely collateral to the charged conduct while still carrying real potential for unfair prejudice. That efficiency-and-fairness tradeoff is why Rule 405 confines specific instances to the narrow situations where character is itself what the case turns on (like a defamation suit where the plaintiff’s actual reputation is a genuine element) or to cross-examination, where a witness can be tested without necessarily proving the underlying incident actually occurred.

Example. A witness testifies about Peter’s reputation for honesty in the community — a straightforward reputation method. Now compare: the opposing party tries to bring up a specific instance where Peter once lied on an unrelated occasion — a more restricted method, generally not allowed on direct examination outside narrow circumstances.

Other-acts evidence is barred for propensity, but allowed for a genuine non-propensity purpose — motive, intent, absence of mistake, identity, common plan, and others (sometimes remembered as “MIMIC”). Even a proper purpose still must survive Rule 403 balancing.

Huddleston v. United States, 485 U.S. 681 (1988), settled a real, practical question about exactly how certain a court has to be that the other act even happened before admitting it. A defendant charged with knowingly possessing and selling stolen videotapes argued that before other-acts evidence (his own prior dealings in stolen merchandise) could be admitted to prove knowledge, the trial judge first had to make a preliminary finding, by a preponderance of the evidence, that the defendant had actually committed the prior act. The Supreme Court disagreed, holding that Rule 404(b) doesn’t require the trial judge to make that kind of independent factual determination at all — the evidence comes in so long as the jury could reasonably find, by a preponderance of the evidence and considering all the evidence presented, that the defendant committed the other act, with the ultimate determination left to the jury itself, not screened out in advance by the judge. The case confirms that 404(b)’s real gatekeeping happens at the purpose-and-relevance stage and the Rule 403 balancing stage — not through a demanding, judge-made certainty requirement about whether the prior act actually occurred.

Example. Peter’s prior theft, using the identical unusual lock-picking technique and cash-only pattern as the current theft, is offered to prove identity — a legitimate non-propensity purpose under 404(b), since the technique is distinctive enough to function as a signature. Now compare: the same prior theft offered simply to show Peter is generally “a thief” — pure propensity, inadmissible regardless of the underlying facts being identical.

A habit — a specific, regular, semi-automatic response to a particular recurring situation — is treated far more freely admissible than character evidence, without needing to fit within Rule 404’s narrower propensity framework at all.

Levin v. United States, 338 F.2d 265 (D.C. Cir. 1964), illustrates how habit evidence can carry real weight even where there’s no eyewitness to the specific event in dispute. A surgeon was sued for operating on a patient without obtaining informed consent, and no witness could testify directly to what happened in the specific pre-operative conversation at issue; the surgeon instead offered evidence of his own established, consistent practice of always personally obtaining written consent before every operation he performed. The D.C. Circuit held this kind of specific, regular professional practice was properly admissible as habit evidence, distinct from a broader character trait like “carefulness” or “conscientiousness,” and genuinely probative of what likely happened on the specific occasion even absent a direct witness. The case is a useful illustration of habit evidence’s real practical value: where direct proof of a specific event is unavailable, a sufficiently regular, specific, semi-automatic practice can substitute for it in a way general character evidence never could, precisely because Rule 406 doesn’t treat habit as mere propensity reasoning.

Example. Peter has a well-documented habit of always locking his car doors — specific, regular, tied to one recurring situation — freely admissible under Rule 406 to argue he likely locked his car on this occasion too. Now compare: evidence that Peter has a general reputation for being “a careful person” — a broader character trait, facing the full Rule 404 propensity framework instead.