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U.S. Supreme Court
KUMHO TIRE CO. v. CARMICHAEL 526 U.S. 137 (1999)

    1. In Daubert, this Court held that Federal Rule of Evidence 702 imposes a special obligation upon a trial judge to “ensure that any and all scientific testimony … is not only relevant, but reliable.” 509 U.S., at 589. The initial question before us is whether this basic gatekeeping obligation applies only to “scientific” testimony or to all expert testimony. We, like the parties, believe that it applies to all expert testimony. See Brief for Petitioners 19; Brief for Respondents 17.

      For one thing, Rule 702 itself says:

      “If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.”

      This language makes no relevant distinction between “scientific” knowledge and “technical” or “other specialized” knowledge. It makes clear that any such knowledge might become the subject of expert testimony. In Daubert, the Court specified that it is the Rule’s word “knowledge,” not the words (like “scientific”) that modify that word, that “establishes a standard of evidentiary reliability.” 509 U.S., at 589—590. Hence, as a matter of language, the Rule applies its reliability standard to all “scientific,” “technical,” or “other specialized” matters within its scope. We concede that the Court in Daubert referred only to “scientific” knowledge. But as the Court there said, it referred to “scientific” testimony “because that [wa]s the nature of the expertise” at issue. Id., at 590, n. 8.

      Neither is the evidentiary rationale that underlay the Court’s basic Daubert “gatekeeping” determination limited to “scientific” knowledge. Daubert pointed out that Federal Rules 702 and 703 grant expert witnesses testimonial latitude unavailable to other witnesses on the “assumption that the expert’s opinion will have a reliable basis in the knowledge and experience of his discipline.” Id., at 592 (pointing out that experts may testify to opinions, including those that are not based on firsthand knowledge or observation). The Rules grant that latitude to all experts, not just to “scientific” ones.

      Finally, it would prove difficult, if not impossible, for judges to administer evidentiary rules under which a gatekeeping obligation depended upon a distinction between “scientific” knowledge and “technical” or “other specialized” knowledge. There is no clear line that divides the one from the others. Disciplines such as engineering rest upon scientific knowledge. Pure scientific theory itself may depend for its development upon observation and properly engineered machinery. And conceptual efforts to distinguish the two are unlikely to produce clear legal lines capable of application in particular cases. Cf. Brief for National Academy of Engineering as Amicus Curiae 9 (scientist seeks to understand nature while the engineer seeks nature’s modification); Brief for Rubber Manufacturers Association as Amicus Curiae 14—16 (engineering, as an “applied science,” relies on “scientific reasoning and methodology”); Brief for John Allen et al. as Amici Curiae 6 (engineering relies upon “scientific knowledge and methods”).

      Neither is there a convincing need to make such distinctions. Experts of all kinds tie observations to conclusions through the use of what Judge Learned Hand called “general truths derived from … specialized experience.” Hand, Historical and Practical Considerations Regarding Expert Testimony, 15 Harv. L. Rev. 40, 54 (1901). And whether the specific expert testimony focuses upon specialized observations, the specialized translation of those observations into theory, a specialized theory itself, or the application of such a theory in a particular case, the expert’s testimony often will rest “upon an experience confessedly foreign in kind to [the jury’s] own.” Ibid. The trial judge’s effort to assure that the specialized testimony is reliable and relevant can help the jury evaluate that foreign experience, whether the testimony reflects scientific, technical, or other specialized knowledge.

      We conclude that Daubert’s general principles apply to the expert matters described in Rule 702. The Rule, in respect to all such matters, “establishes a standard of evidentiary reliability.” 509 U.S., at 590. It “requires a valid … connection to the pertinent inquiry as a precondition to admissibility.” Id., at 592. And where such testimony’s factual basis, data, principles, methods, or their application are called sufficiently into question, see Part III, infra, the trial judge must determine whether the testimony has “a reliable basis in the knowledge and experience of [the relevant] discipline.” 509 U.S., at 592.