the defendant was attending to weighing the credibility of the story in this example is substantially outweighed by a danger of unfair prejudice as the majority of Americans would view the defendant's participation in the Knights of the Ku Klux Klan to be immoral and is therefore inadmissible. While the rules proscribe certain testimony from being admissible for one purpose, but it may be admissible for another. An example of this is Rule 404, specifically 404(b) as it pertains to specific instances of a person's conduct. While 404 generally prohibits use of prior acts and crimes to show that a defendant acted in accordance with those prior acts or crimes, 404(b) provides: Essentially testimony about an act a person has committed in the past is not admissible for the purposes of showing it is more likely that they committed the same act, however it could be admissible for another purpose, such as knowledge or lack of mistake. For example, in a DUI case, the prosecutor may not admit evidence of a prior instance of driving impaired to show that the defendant acted in conformity and drove impaired on the day he is charged with doing so. However such evidence may be admissible if the defense has argued the defendant had no knowledge driving impaired was a crime. Evidence of his prior arrest, conviction, or other circumstances surrounding his prior instance of impaired driving then becomes admissible to rebut the claim of "mistake." The testimony is now being offered not for conformity but to demonstrate knowledge or lack of mistake. Other common-law concepts with previously amorphous limits have been more clearly delineated. This is especially true regarding hearsay evidence. Among scholars and in historical judicial decisions, four related definitions of "hearsay" emerged, and the various exceptions and exemptions flowed from the particular definition preferred by the scholar or court. The Federal Rules of Evidence settled on one of these four definitions and then fixed the various exceptions and exemptions in relation to the preferred definition of hearsay. On the other hand, the law of privileges remains a creature of federal common law under the Rules, rather than the subject of judicial interpretation of the text of the rule. Just as the Uniform Rules of Evidence had, the advisory committee draft of the rules that the Supreme Court formally transmitted to Congress codified nine evidentiary privilegesrequired reports, attorney-client, psychotherapist-patient, husband-wife, communications to