Excerpt from Brewer, Scientific Expert Testimony and Intellectual Due Process, 107 Yale Law Journal, 1535, 1673-1679 (1998) (most footnoted omitted).


A. Epistemic Nonarbitrariness as a Practical Constraint on Legitimate Epistemic Deference

My goal for the present section is to explicate some of the overall normative aims in the "practical point of view" from which a legal system ought to evaluate the transfer of scientific information from scientific experts to nonexpert judges and jurors. The normative aims that are such an important element in the practical point of view of a legal system are articulated and relied upon in many decisions by courts dealing in one way or another with the rationality of legal decisionmaking in cases to which complex scientific information is rationally pertinent. I discuss a few such cases to help explicate what those normative aims are.

The central idea animating these practical norms is that certain rule-of-law values require epistemic nonarbitrariness in factfinding reasoning, as in other types of reasoning. Thus, if the nonexpert cannot acquire scientific beliefs from competing experts in a way that is nonarbitrary, from an epistemic point of view, those beliefs will therefore not be legitimate from the practical legal point of view. That is, according to this practical rule-of-law norm, at least in cases in which life, liberty, or property is at stake, epistemic nonarbitrariness in the process of "finding" scientifically discerned facts is a necessary condition of the practical legitimacy of a decision that relies on that factfinding.

One finds respect for and recognition of this norm in both philosophical and legal materials. John Rawls, for example, has long maintained that among those "guidelines intended to preserve the integrity of the judicial process" are the requirements that courts undertake conscientiously to determine whether an infraction has taken place.... Thus a legal system must... contain rules of evidence that guarantee rational procedures of inquiry. While there are variations in these procedures, the rule of law requires some form of due process: that is, a process reasonably designed to ascertain the truth, in ways consistent with the other ends of the legal system, as to whether a violation has taken place and under what circumstances.

Rawls's point applies no less to the integrity of the judicial process in civil cases than it does to the integrity of that process in criminal cases. A reflection of this same basic rule-of-law value, articulated in the setting of a civil antitrust action, is found in a prominent federal appellate case. In In re Japanese Electronic Products Antitrust Litigation, (37) several U.S. electronics manufacturers brought an antitrust action against several Japanese manufacturers. When the U.S. plaintiffs made a motion for jury trial, the defendant Japanese companies countered, claiming among other things that the economic and technical issues were too conceptually complex for the jury to understand, even with the help of expert testimony. The case was on appeal from a federal district court on the sole question whether the plaintiffs had a right to a jury trial even when the issues and evidence involved would be acutely complex. In effect, the court considered whether there was (what has come to be referred to as) a "complexity exception" to the Seventh Amendment right to jury trial under the U.S. Constitution. The district judge had held that there was no such "complexity exception." In what appears to be an unprecedented decision in the federal courts, the appellate court overturned the district court judgment. The appellate court agreed with the defendant, vacated the district court's pretrial order, and held that, despite the normative force of the Seventh Amendment right to jury trial, the Fifth Amendment due process right to have a rational and fair adjudication outweighed the Seventh Amendment right. The court concluded that the Fifth Amendment narrows the scope of the Seventh Amendment by means of a complexity exception.

In its cogently articulated opinion, the appellate court specified the kind of complexity that might trump the right to jury trial as follows:

A suit is too complex for a jury when circumstances render the jury unable to decide in a proper manner. The law presumes that a jury will find facts and reach a verdict by rational means. It does not contemplate scientific precision but does contemplate a resolution of each issue on the basis of a fair and reasonable assessment of the evidence and a fair and reasonable application of the relevant legal rules. A suit might be excessively complex as a result of any set of circumstances which singly or in combination render a jury unable to decide in the foregoing rational manner. Examples of such circumstances are an exceptionally long trial period and conceptually difficult factual issues.

The court concludes that "due process precludes trial by jury when a jury is unable to perform this task with a reasonable understanding of the evidence and the legal rules." The court went on to elucidate the connection between this right to rational comprehension by the legal decisionmaker and rule-of-law values like predictability and notice:

The due process objections to jury trial of a complex case implicate values of fundamental importance. If judicial decisions are not based on factual determinations bearing some reliable degree of accuracy, legal remedies will not be applied consistently with the purposes of the laws. There is a danger that jury verdicts will be erratic and completely unpredictable, which would be inconsistent with evenhanded justice. Finally, unless the jury can understand the evidence and the legal rules sufficiently to rest its decision on them, the objective of most rules of evidence and procedure in promoting a fair trial will be lost entirely. We believe that when a jury is unable to perform its decisionmaking task with a reasonable understanding of the evidence and legal rules, it undermines the ability of a district court to render basic justice.

The court also addressed the question of what values the legal system might injure in cases to which the complexity exception applied by choosing not to allow the kind of community input that the constitutional jury trial right was designed to secure. The central values often mentioned in connection with the jury trial right - values powerful enough, in the district court's judgment, to lead it to reject the idea of a complexity exception - are the jury's function as a check on judicial power, and the jury's ability to modify and conform the law to, and suffuse the law with, community values (so-called jury equity), thereby lending the law a communitarian legitimacy it might not otherwise have. Assessing these countervailing values reflected in the Seventh Amendment, the court of appeals delivered something of a coup de grace debater's point:

In the context of a lawsuit of the complexity that we have posited, however, these features [of the jury system] do not produce real benefits of substantial value. The function of "jury equity" may be legitimate when the jury actually modifies the law to conform to community values. However, when the jury is unable to determine the normal application of the law to the facts of a case and reaches a verdict on the basis of nothing more than its own determination of community wisdom and values, its operation is indistinguishable from arbitrary and unprincipled decisionmaking. Similarly, the "line-drawing" function is difficult to justify when the jury cannot understand the evidence or legal rules relevant to the issue of where to draw a line.

... A jury unable to understand the evidence and legal rules is hardly a reliable and effective check on judicial power. Our liberties are more secure when judicial decisionmakers proceed rationally, consistently with the law, and on the basis of evidence produced at trial. If the jury is unable to function in this manner, it has the capacity of becoming itself a tool of arbitrary and erratic judicial power.

In In re Japanese Electronic Products Antitrust Litigation, one thus finds a powerful articulation of the legal system's commitment to practical norms in the family of rule-of-law values that are specifically addressed to the epistemic cogency of juridical factfinding. In various ways, one finds a similar commitment to these epistemically oriented rule of law values in many other judicial opinions, state and federal. Thus, one state supreme court declared:

One cogent reason for overturning the verdict of a jury is that the verdict is based on conclusions that are physically impossible. "[A] verdict should be set aside "where testimony is thus in conflict with indisputable physical facts, the facts demonstrate that the testimony is either intentionally or unintentionally untrue, and leave no real question of conflict of evidence for the jury concerning which reasonable minds could reasonably differ.'...."

Scientific evidence is relevant to a determination of what is physically impossible. In Roma v. Thames River Specialties Co., this court held that the trial judge "would have failed in his duty" if he had not set aside the verdict when "the laws of mechanics, as testified to and uncontradicted, tended to prove [the claimant's] story impossible." In Jump v. Ensign-Bickford Co.the trial court properly set aside the verdict when expert scientific testimony indicated that it was physically impossible for a fuse to burn as fast as the claimant had alleged, and this court could "find in the evidence no reasonable ground which would have justified the jury in disregarding that evidence." (38)

Similarly, in an opinion perhaps signaling that the U.S. Supreme Court may be amenable to something like a complexity exception, Justice Souter declared that, when a case requires the legal decisionmaker to interpret and comprehend complex technical patents, the decision is to be made by the judge, not the jury. He reasoned:

In the main, we expect, any credibility determinations will be subsumed within the necessarily sophisticated analysis of the whole document, required by the standard construction rule that a term can be defined only in a way that comports with the instrument as a whole.Thus, in these cases a jury's capabilities to evaluate demeanor, to sense the "mainsprings of human conduct, "or to reflect community standards... are much less significant than a trained ability to evaluate the testimony in relation to the overall structure of the patent. The decisionmaker vested with the task of construing the patent is in the better position to ascertain whether an expert's proposed definition fully comports with the specification and claims and so will preserve the patent's internal coherence. (39)

These cases suggest a strong commitment among leading jurists to the idea that factfinding, including factfinding regarding matters that are the special epistemic province of expert scientists, must be conducted in a coherent and rational manner in order that this epistemic process meet the normative requirements of a legal system that operates to grant or deprive people of life, liberty, and property. Reflecting on these and other such statements by judges and other jurists, we may sense a commitment, immanent in the broad materials that constitute authoritative law (U.S. law, at least), to what we may call the practical norm of intellectual due process. In re Japanese Electronic Products Antitrust Litigation is especially fertile here, with its suggestion that the epistemic process of comprehension of theoretical complexities is a mandate of the decidedly practical norm of the Due Process Clause. Though there are, to be sure, many features of due process that do not specifically "sound" epistemic, that case reveals that some distinctively practical norms do have meaningful epistemic consequences. Much philosophical work remains to be done to explicate this emerging rule-of-law norm. Recognition of intellectual due process as a practical norm in the family of rule-of-law norms has only just begun - partly because the startling advances in scientific methods - coupled with the striking increases in the technological complexity of society and the laws that arise to govern and guide it, is also a relatively recent socio-epistemic phenomenon.

A great deal of work remains in explicating the scope and criteria of "intellectual due process," but this much seems clear even now: A reasoning process that is epistemically arbitrary is incapable of producing a legitimate decision, for such a reasoning process is "indistinguishable from arbitrary and unprincipled decisionmaking." If I am right that practical epistemic deference to expert scientists is doomed, on average, to generate in nonexpert judges and jurors beliefs that are only accidentally and arbitrarily true at best and thus are not epistemically justified beliefs, then this process perforce does not produce legally legitimate decisions.

B. Consequences for Doctrinal and Institutional Design: "Two-Hat" Solutions and Intellectual Due Process

What is to be done? Detailed analysis of the consequences of this analysis for institutional and doctrinal revision and transformation are beyond the scope of my current project. A few conclusions do emerge, however. If legal systems are to endorse and aspire to satisfy the intellectual due process norms (and other related rule-of-law norms), they would be well advised to move toward a "two-hat" model of legal decisionmaking in areas to which scientific results are rationally pertinent. On this model, the system seeks to ensure that one and the same decisionmaker has both legal legitimacy (by being duly elected or appointed by a legitimate elective or appointing authority) and epistemic competence with the basic formal tools of scientific analysis. A useful heuristic analogy might be that of a mathematician or physicist who has practical decisionmaking authority as a voting member of his department (wearing one hat), and epistemic competence that informs the practical judgment (wearing the other), or similarly, a physicist voting on who should receive a physics prize for the most important contribution to his field. Many jurists have already begun to consider different paths on this broad avenue of reform, and various proposals consistent with the "two-hat solution" satisfy it. These include turning over many decisions currently made by private litigation to public administrative agencies staffed with trained scientists, relying on blue ribbon scientifically trained juries, scientific expert magistrate judges, or even special science courts staffed by scientifically trained judges. Already in the wake of Daubert's increased demands on federal trial court judges, special workshops on scientific theory and method have become available to train them.

A further word about Daubert's gatekeeping solution is in order. Both Daubert and In re Japanese Electronic Products Antitrust Litigation rely on the underlying assumption that a judge is in a decisively better epistemic position than a jury to assess rationally the merits of competing scientific testimony, even when the underdetermination condition is satisfied. My analysis of the legitimacy of epistemic deference gives reason to be skeptical about that assumption, for the analysis applies no less to a nonexpert judge than it does to a nonexpert jury. It is for this reason that the distinction between the threshold question of the admissibility of evidence, on the one hand, and the question of the weight of the evidence, on the other, is not particularly important in my analysis. Daubert and (implicitly) In re Japanese Electronic Products Antitrust Litigation treat this distinction as very important, for they both assume that a judge is in a significantly better epistemic position to decide whether proffered scientific evidence is sufficiently reliable to be admissible in a trial before a nonexpert jury, which could then weigh the suitably screened evidence. I have argued that we have good reason to doubt that assumption and, indeed, to be quite skeptical about the idea of solving problems of selection, competition, and underdetermination by taking decisions about expert testimony away from nonexpert juries and giving them to nonexpert judges.

It is important not to overstate my argument here. Early in the Article, I noted that epistemic competence is a matter of degree - that not all experts are equally epistemically competent and not all nonexperts are equally epistemically incompetent. This means that it is certainly conceptually possible that a trial judge is significantly more epistemically competent than a jury in assessing the scientific merits of expert scientific testimony, even when the underdetermination condition is satisfied. That is, it is conceptually possible that the underlying assumption of Daubert, In re Japanese Electronic Products Antitrust Litigation, Markman, and many other state and federal cases, is accurate as to some judges. Nor is this a bare conceptual possibility. It is not unreasonable to suppose that some judges, who are repeatedly and predictably faced with proffers of scientific evidence, may find and take the time and energy required to become decently competent in manipulating the aims, methods, and results of some of the specific sciences that are likely to come into their courts. Perhaps some autodidactic judges even become sufficiently competent to satisfy the demands of intellectual due process. The plausible possibility that this is true of some judges raises the largely empirical question about what percentage of judges in state or federal systems are in fact in this happy - from the point of view of intellectual due process - state.

Still, though I have not done the kind of empirical work required cogently to answer that question, the norm of intellectual due process itself places the burden of empirical proof on those who would maintain that a large enough percentage of judges are or will in the near future be in that state. That is, the burden is on the person who claims, along with the Daubert Court, that, by and large, trial judges already wear, or soon will wear, the required "two hats." The burden is on the person who claims that the requirements of intellectual due process can be satisfied on a large scale by taking the decisions out of the hands of nonexpert juries and leaving them in the hands of judges. Carrying that burden of proof would of course call for a procedure significantly different from that of Daubert itself, for Daubert is still willing to turn over many ultimate decisions, even in cases in which the underdetermination condition is satisfied, to nonexperts whom we have no reason to believe are sufficiently competent in the expert discipline to meet the requirements of intellectual due process.

I have spoken of remaining empirical questions and of burdens of empirical proof. There are also important conceptual details that remain to be worked out for the two-hat solution. What kind of training should the experts - or expertly trained judges - get? One can get a clear sense of the training required to have basic competence in biology, genetics, statistics, economics, or epidemiology, but how scientifically specialized is it feasible to allow the two-hat-wearing legal decisionmaker to be? Even the heuristic analogy of the mathematician may break down, since that field, like virtually all fields in the empirical and demonstrative sciences, is becoming intensely specialized. Will scientific discipline become so specialized that it ceases to make sense to talk about general epistemic competence even within a discipline? And if that problem looms for singular disciplines, what hope is there for resolving problems of extra-disciplinary competition in a manner consistent with the suasions of intellectual due process? Still another question is, how much training is enough? To the level of a Ph.D? An M.A.? Are formal degrees good signals at all? Still another question involves the democratic legitimacy of the two-hat solution. Rule by technocrat-kings has its dangers, just as does rule by epistemically unruly mobs. Is there a feasible and meaningful way in which a responsible polity can deliberate and endorse the training programs and institutional schemes that would implement the "two-hat" solution and achieve a reasonable degree of intellectual due process?

These are deep and difficult questions. But few topics, I hazard to say, will be more important to the health of the polity and its citizens than the close investigation of how the law ought - from legal, moral, and other closely related practical points of view - to keep up with science.


Though its steps have been long, the argument presented in this Article is not too difficult to summarize. I have argued that there is a structured reasoning process that a nonexpert judge or jury must use in an effort to take account of scientific expert testimony in the course of reaching a legal decision about liability (in the civil setting) or guilt (in the criminal setting). When one attends carefully to the precise steps of the reasoning process, one sees that there are crucial steps that a nonexpert judge or jury is, in a great many instances, not capable of performing in an epistemically nonarbitrary manner. Specifically, when competing scientific experts are, for all the nonexpert knows, fairly evenly matched in credentials, reputation, and demeanor, and when no generally accessible rational criteria (such as self-contradiction by an expert witness) break the "tie" (i.e., when what I have called the "underdetermination condition" is satisfied), then a nonexpert is not capable of choosing among the competing experts in an epistemically nonarbitrary way. I have also sought to show that epistemic nonarbitrariness is a necessary condition of legitimacy, as expressed in the norm of intellectual due process. This norm, an emerging rule-of-law norm, immanent in both decided cases and various analyses of jurists and philosophers, will be increasingly important as scientific expert testimony comes to be used in a greater and greater percentage of cases. n441 When the conditions of this norm are not satisfied, decisions by nonexperts, even in light of relevant scientific expert testimony, lack epistemic legitimacy, and therefore lack the kind of practical-cum-moral legitimacy that legal systems do and ought to demand.

What is to be done if the relevance of scientific information to legal decisions continues to grow, while nonexperts are so often incapable of legitimately incorporating that information into their decisions? Nothing in this Article suggests that a nonexpert judge cannot become sufficiently epistemically competent, even without the formal training of a scientist. Perhaps some judges, by virtue of background or repeat "on the bench" experience with scientific evidence, will become sufficiently epistemically competent to render decisions about scientific expert testimony that are epistemically legitimate and that meet the demands of intellectual due process. Daubert itself calls upon judges to be more active as "gatekeepers" in screening out unreliable science. But Daubert's solution to the problem of legitimately assessing expert scientific testimony seems a poor one. First, given the press of other judicial business, it seems unlikely that a significant percentage of judges either already have, or will find the time to acquire, the kind of scientific competence that legitimate, intellectually "duly processed" decisionmaking requires. That is, unless judges are routinely and systematically trained in scientific theories and methods, Daubert does not offer a promising overall solution to the problem. Also, under Daubert, even when a judge is sufficiently competent, that competence could yield a duly processed, legitimate decision only when the judge decides not to admit some proffered scientific testimony. But in a great many other cases, the judge will admit competing scientific evidence, and allow the nonexpert, noncompetent jury to make the decision - the quintessential circumstance, as this Article has argued, in which failures of intellectual due process occur.

Nor can the expedient emphasized by Justice Breyer in the Joiner decision - the Supreme Court's next major treatment of an issue concerning scientific evidence after Daubert - resolve the problem. Justice Breyer rightly highlighted the epistemic problem judges have in attempting to fulfill Daubert's requirements:

This requirement will sometimes ask judges to make subtle and sophisticated determinations about scientific methodology and its relation to the conclusions an expert witness seeks to offer - particularly when a case arises in an area where the science itself is tentative or uncertain, or where testimony about general risk levels in human beings or animals is offered to prove individual causation. Yet... judges are not scientists and do not have the scientific training that can facilitate the making of such decisions. (40)

In Justice Breyer's view, given this challenge, judges should more actively solicit scientific information in order to perform their Daubert-mandated role of "gatekeepers" vigilant against junk science, for example by using court appointed experts, appointing special masters or specially trained law clerks, or using pretrial conferences to narrow the scientific issues. But, for reasons suggested above, this solution also fails to meet the needs of intellectual due process for any judge who is himself not epistemically competent in scientific methods and theories. For the judge is not capable of making an epistemically legitimate decision about which special master, law clerk, or court-appointed expert to consult.

The only solution (actually, it is a family of solutions) I see requires that one and the same legal decisionmaker wear two hats, the hat of epistemic competence and the hat of practical legitimacy. That is, whether it is a scientifically trained judge or juror or agency administrator, the same person who has legal authority must also have epistemic competence in relevant scientific disciplines. In an age in which culture will increasingly take advantage of the massive intellectual power of science, this is not too high a price for the legal system to pay to satisfy its own just intellectual aspirations.

37. 631 F.2d 1069 (3d Cir. 1980).

38. State v. Hammond, 604 A.2d 793, 795 (Conn. 1992) (citations omitted)

39. Markman v. Westview Instruments, Inc., 116 S. Ct. 1384, 1396 (1996) (citations omitted). From an epistemic point of view, Markman's solution suffers from the same problem that afflicts In Re Japanese Products Antitrust Litigation: A technically nonexpert judge is not in a decisively better position than a technically nonexpert jury.

40. Id. Joiner held that, even under Daubert, the proper standard of review for decisions about the admissibility of scientific evidence was "abuse of discretion," regardless of whether the district judge's decision was to admit or exclude the evidence, and regardless of whether that decision was "outcome determinative." See id. at 515 (majority opinion).


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