The character evidence rule bars the use of propensity to show conduct:

Propensity --------//--------> Conduct

By implication the rule also bars the use of specific instances of other conduct in order to show propensity for the purpose of showing the conduct in issue.

Thus,

Other Conduct ------> Propensity --------> Conduct in Issue

is not permitted.

This rule (and its implication for the evidentiary use of other conduct) protects, of course, criminal defendants.

The rule, furthermore, applies to people other than criminal defendants. For example, a defendant in a personal injury case is not allowed to show that the plaintiff has a propensity to be careless in order to show that the plaintiff acted carelessly at the time of the collision between the plaintiff and the defendant.

Plaintiff's propensity toward carelessness -----//-----> Plaintiff's careless conduct at time of accident

There are exceptions to the prohibition against proof of conduct by character or disposition.

One exception allows a criminal defendant to offer a pertinent trait of his or her own character to show his or her non-commission of the crime charged.

A second set of rules allows the use of character evidence under certain defined circumstances to impeach and rehabilitate witnesses.

A third exception allows a criminal defendant to offer the character or disposition of the alleged victim of the crime to show the probable behavior of the alleged victim. For example, a criminal defendant on trial for murder may offer evidence of the violent disposition of the dead person (and alleged homicide victim) to show that the victim attacked the defendant, causing the defendant to kill the alleged victim in self-defense.

The common law allowed a defendant in a rape case to show the alleged victim's "unchaste" character in order to bolster a defense of consent (to intercourse).

It is not clear that the common law rule allowing the use of the rape victim's sexual propensities can be viewed or explained as just a special case of a more general rule allowing criminal defendants to show the character trait of the alleged victim of a crime; this is because, rape cases aside, the common law generally allowed only defendants in homicide cases to show the character of the victim. But the drafters of the Federal Rules of Evidence adopted the rule that any criminal defendant could show a pertinent character trait of the alleged victim, and the drafters viewed the rape defendant's right to show the victim's sexual propensity as a special case of this general rule. See the Advisory Committee's Note to FRE 404(a)(2).

Old films and anecdotes sometimes depict a courtrrom tactic in which a rape defendant back in the not-so-good old days trots out various old buddies of his to testify that they too had intercourse -- consensual intercourse -- with the victim. In fact, this tactic, though sometimes attempted, was generally rejected. Though the common law allowed rape defendants to show the victim's character for unchastity, the evidence of this disposition, like other character evidence made exceptionally admissible, had to take the form of reputation evidence, and could not consist of specific instances of conduct. It is true that defense lawyers sometimes argued that the victim's specific instances of conduct of unchastity were admissible to impeach the victim. But this argument also generally failed -- since most courts and judges took the view that acts of unchastity (so-called) did not in and of themselves impugn the credibility of the victim. In any event, such instances of unchastity, under settled rules limiting the use of extrinsic evidence to impeach on a collateral matter, could not be shown by extrinsic evidence, but could only be inquired into during the cross-examination of the alleged rape victim. It is true that Wigmore had argued that the victim's specific acts of unchastity should be admissible, both to show the victim's consent and to impeach her. He also even argued that every rape victim, as a precondition for any rape prosecution, had to be made to submit to a psychiatric or psychological examination. But in this instance Wigmore's ordinarily-influential views did not prevail; a few courts now and then went in the direction that Wigmore wanted them to go but in the main they stuck with the common law restrictions on the use of evidence of the alleged rape victim's lack of chastity.

As already noted, there was not -- at least not nominally -- an exception to the character evidence rule for the character and conduct of criminal defendants. Indeed, the use of character evidence against criminal defendants may be the paradigmatic vice or phenomenon at which the character evidence rule was and is directed. Hence, as a general matter, not only could a prosecutor not show that a criminal defendant had the reputation of being the kind of person who would commit the crime charged, but a prosecutor also could not show that a defendant had committed crimes or wrongs on other occasions in order to show that a criminal defendant was the sort of person likely to commit the crime charged. Nonetheless, there were and are a number of settled doctrines that limit the reach of the character evidence prohibition in criminal cases. First, if a criminal defendant chooses to testify, his prior misdeeds may sometimes be used to impeach him or her. Second, if a misdeed of the defendant is used to show the defendant's commission of the crime by showing not the defendant's disposition but any other matter that tends to show the commission of the crime charged, the misdeed is not barred by the character evidence rule. For example, the prosecutor may show that defendant robbed a safe in the immediate vicinity of the crime charged in order to show defendant's opportunity to commit the crime charged. Third, if a misdeed is offered to show not conduct by the defendant but some other matter -- such as a defendant's knowledge, intent, or plan--, the misdeed is not barred by the character evidence rule. Finally, in many states these limitations (and some others) were and are stretched almost beyond recognition in child sexual abuse cases or in sex crime prosecutions generally to make sexual wrongdoing by the defendant on other occasions quite freely admissible. In particular, the defendant's sex crimes on other occasions were and are frequently admissible in child sexual abuse prosecutions to show the defendant's lustful disposition or depraved sexual instinct.

It was against this background that jurisdictions adopted, first, rape shield laws and, more recently, rules patterned on Federal Rules of Evidence 413-415. The William Kennedy Smith case is, I think, a good crucible for examining this swirl of doctrine, doctrinal complexity, and, sometimes, outright confusion in the judicial mind. (I have not mentioned every pertinent wrinkle of the character evidence rule. But I have mentioned more than enough for one day.)