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The Expert Witness: Truth-Ception of Rational Inferences

Author: Gerard Dondero
Date: 15.06.2020 Time to read: 10 min

There’s a lone locomotive hurtling over the tracks, engine puffing smoke at the sky. The journey is almost over, and the train is making excellent time. But the track ends at a cliff --- and the fall off that edge is from a height that nothing can survive. A few minutes before doom, a parachuted silhouette falls from the sky and makes a miraculous drop on the front car through the thick smoke. He flips the hatch and drops inside. The train lurches as he takes control, braking for just one second, then steers the train right past the edge; tracks begin to build themselves over the empty expanse. The train crosses the ravine without incident.

Close call.

You wake up…on the same train, headed in the same direction, with the same oncoming issue. This time, however, there are several other people in the car with you. And they just all had the same dream you did. Except this time…the parachuted figure is absent. You all band together, head to the front car, and steer toward the ravine just like the figure did. And…history repeats itself. The train chugs over but above the abyss.

Just as you’re about to shrug it off as déjà vu, you see him there, pipe in hand, leaned against the entry door of the command room. “Took you long enough to see it my way.” Puff, ha, puff.

In a jury trial, any inference about the ultimate issues of fact must be rational --- correctness matters less than the process. The rules of evidence combined with cross-examination and a layman’s capacity for reason suffice oft-times to guide a rational inference about the evidence. But for all other situations, an expert witness is that emergency conductor, infiltrating a juror’s mind to plant a rational inference that the juror would never have had. So doing, the expert witness preserves rationality in the juror's thought process. And without the expert witness’s guidance, the jury trial would assuredly fail to reach a rational decision about historical fact.

Did the jurors understand the expert witness’s testimony, or his parachute, or his steering, or the tracks?

It’s irrelevant.

Legitimacy Station

All jury trials have one destination in mind: historical knowledge about the events of legal interest. The definition of knowledge has generally been “justified true belief.” Many scholars believe that the rules of evidence and jury trial procedure are dedicated to seeking truth. Assuming that "true" implies a correspondence theory of truth rather than a more "consensus reality" theory, there is a problem with what is "true."

It's at least reasonable to surmise that we are unable to ever have enough rational justifications for anything to claim with 100% certainty that that thing is true. And as we know, the court is a human institution. Yet, even if below 100% of the decisions are true, an institution can still seek truth. Here we look to how "sticky" its beliefs are in the face of conflicting evidence.

Unfortunately, with the court, it's more than truth falling outside the borders of "what humans can guarantee" that causes us to doubt its "truth-seeking" status. Mainly, the existence of exonerations --- in high numbers too --- and the difficulty involved with voiding a judgment in the face of new evidence. These facts, among others, disconfirm any belief that the court concerns itself with knowledge per se. Other priorities are more important to the court than the search for truth (we never doubt that the court has this as an aim, it is just lower priority than other aims).

This want refocuses us to the rest of the definition: justified and belief. A belief is one’s acceptance of a proposition or statement as if it were true. The inverse regarding truth holds here: most any person and institution is capable of this feat.

Now, we turn to the last part of the definition, justification. Ultimately, the aim of any political institution --- which the jury trial is one --- is legitimacy. Legitimacy necessitates satisfying conditions for exercising power. Consequently, justification matters more than ultimate truth in the sphere of political legitimacy. For a political institution of any kind --- including that of a jury trial --- any decision that the institution will enforce with violence must be “prudentially rational, morally acceptable, or both.”  

Therefore, while the court seeks truth --- earnestly we hope --- it's different from a knowledge institution. Its highest priority is justification. Truth and knowledge are inseparable; a knowledge institution can only know what is true. The court can know whatever it has adjudicated on the merits. The state will back the decision with violence and the decision effects either liberty or property of the litigating parties. To grok the difference, Justice Scalia, writing for the Supreme Court of the United States, has held that factual innocence fails to constitutionally bar the death penalty post-conviction.  The court's decision are meant to be final and impregnable to challenge.

So while there is considerable overlap between what the jury trial does and knowledge, the purposes are distinct. Contrast the court's business with a field like science, which concerns itself with what is true (or what at present has yet to be falsified) without much regard to the process of theory generation or whether later evidence disconfirms the theory.

"It is whether or not the theory gives predictions that agree with experiment. It is not a question of whether a theory is philosophically delightful, or easy to understand, or perfectly reasonable from the point of view of common sense.”

Justification is second priority for science. And also unlike science, which mobilizes community resources in such a way that minimizes asymmetries due to social power and prestige (though far from eliminates them), the court remains vulnerable to these political pressures. It even acts as a conduit for scientific fields to battle it out in a public forum. And the court's sensitivity is necessary to preserve order.

Reason rolling out on the train tracks of evidence

Rationality: the Fuel

Assuming for a moment that “due process” (delimit that notion to the jury trial alone) checks the “morally acceptable” box, that leaves only the “prudentially rational” box. Consequently, whatever decision the tribunal reaches must rise from reason. This destination is different from “true belief about the events of interest to the law,” although one hopes a correlation exists.

Trials, as we have said, are there to (1) ascertain a set of facts and (2) apply some principle to resolve a dispute over those facts. And with the jury trial, reason is the touchstone of how juries evaluate evidence, so the court’s conviction originates from the reasonable inferences of the jury.

The theory of the law is that when such material or evidence is put before the trier of fact, the findings of fact will depend upon the conviction made upon the minds of a rational group of men. In other words, the finding of the operative elements of any litigated transaction depends upon the reasoning process of persons with the ordinary degree of knowledge and experience, who make necessary inferences

Note that the preceding paragraph fails to mention “truth,” even one time. Given that, for legitimacy’s sake, reason must source the tribunal’s decision, the process must take great care ensuring a reasonable thought process for the jury. Indeed, unlike a witness, a juror has a high obligation to ensure all beliefs are reasonably held:

A witness swears to what he has seen and heard … to what hath fallen under his senses. But a juryman swears to what he can infer and conclude from the testimony by the act and force of the understanding

Accordingly, these conditions justify safeguards to ensure a rational decision-making process. Epistemic paternalism is the theory that there are certain situations where it is appropriate or morally permissible to interfere with (1) an agent’s ability to gather and inquire about information, (2) without consulting the agent, and (3) to make them epistemically better off. Suffice it to say, that with stakes this high, the jury trial seems to be one fit for epistemic paternalism.

Consequently, the expert witness must persuade the juror to welcome this mental hijacking and accept it as reliably as their own thoughts. Incepting a reasoning process is a fait accompli --- if done right.

The Rules of Evidence and Cross-Examination: The Engine and Tracks for the Brain Train

That the situation calls for epistemic paternalism to preserve the rational inference is different from the rules of evidence being historically created for that purpose. Though, it is certainly expedient to view the rules in this light.  And the research does point to several reasons for assuming epistemic paternalism pervades the jury trial process; the fears early judges had about laymen find themselves realized in empirical studies:

 [R]ecent research on our dual tendency for bias and overconfidence suggests that we cannot rely on ourselves for epistemic improvement, and that our best bet is to instead impose certain external constraints on information access, collection and evaluation.

But there are several competing theories regarding why the rules of evidence exist. Perhaps the rules incentivize lawyers to produce the best evidence. Maybe the rules attempt to correctly allocate the risk of erroneous evidence. Or the rules are just there to protect us from the “worst evidence” that lawyers will doubtless attempt to produce. Adding to that, the historical account portraying evidentiary rules as there to protect us from juror bias may be flawed.

But, the epistemic paternalism, “jury control” paradigm finds force along many routes. First, the law ipso facto is a paternalistic enterprise, designed to protect others from acting against their own self interest. Others decide this self-interest, of course.

Second, scholars who were more contemporaneous with the edification of evidence law --- Thayer and Wigmore --- championed a ‘jury control’ vision of the rules.

Third, even if the rules sprung up to control lawyers, such a need speaks to sophistry swaying the jury. A lawyer’s main objective is to persuade --- by any means within the law. Lawyers would never use arguments and tactics lawyers that failed to persuade. So, if it is true that we have a natural tendency to intellectual sloth and heuristic-making, then a layman will fail to detect lies and bad argumentation.

Which, naturally, leaves “jury control” epistemic paternalism as the best paradigm standing. The rules of evidence are train tracks carrying the rational inference.

Tracks and a train need an engine. According to evidence’s Paul Bunyan, John Henry Wigmore, cross-examination is “beyond any doubt the greatest legal engine ever invented for the discovery of truth.” And judging by the amount of judges who have quoted him, the courts agree. Cross-examination powers the jury’s thought processes as they analyze evidence.

The Expert Witness: Taking the Train Where You Thought It Couldn’t Go --- YOUR MIND

While it may have seemed like a wacky characterization at the time, an expert witness truly is meant as a juror’s thinking cap:

The expert's function is to supplement the premises upon which the reasoning of the trier of fact is based with those premises obtained from his experiential qualifications, thereby endowing the trier of fact with sufficient knowledge to understand the significance of the evidence and to make the inferences. It is evident, therefore, that the fiat for expert testimony is necessity, born of the realization that the effective administration of justice requires aid from other branches of learning and science.

So, the expert witness is essentially there to advocate on behalf of his particular reasoning process and get the jury to adopt it as their own. This is epistemic paternalism within epistemic paternalism, as he is interfering with the juror’s thinking process for their epistemic betterment without first seeking consent within the larger context of a jury trial interfering with the juror’s thinking process for their epistemic betterment without first seeking consent (jury duty is mandatory).

The juror effectively is at a point where, even with the court’s efforts, their minds fail to proceed along the tracks. The evidence is likely too complex for them to make heads, tails, or sense of. Thus, the expert witness has to insert a reasoning process into their minds that would allow them to make a reasonable inference about the evidence.

Of course, a juror may refuse the reasoning process that the expert witness offers. Consequently, the expert witness must persuade the juror to welcome this mental hijacking and accept it as reliably as their own thoughts. Incepting a reasoning process is a fait accompli --- if done right.

An expert witness spotted on the job

Expert Witness as Reason Within Your Reason

One justification for epistemic paternalism --- of the kind now seen within itself --- is that the thought meddler must themselves be an “expert.” Indeed, “expertise is the prime epistemic factor in the defense of epistemic paternalism.”

There are two roads the expert witness may travel: (1) make the juror understand the reasoning process itself, or (2) convince the juror to “take his word for it.”

Either method of coaxing is valid and reasonable. Strains of scholarship bristle at the ineptitude of juries and lament the failure of (1):

Almost a century ago Justice Learned Hand recognized the limitations of the lay jury. He concluded that in resolving conflicts or inconsistencies in expert testimony "[t]he jury is not a competent tribunal." ' In fact, "[i]t is just because they are incompetent for such a task that the expert is necessary at all."' Hand based his conclusion on the fact that a jury lacks the experience necessary to understand the validity of the laws or propositions used by the experts." Hand considered the problem intractable, causing him to propose the widespread use of court appointed experts who would provide the jury "the final statement of what was true."' Therein lies the age old conundrum: how can the system give the jury the assistance it needs to resolve conflicts in expert testimony without overwhelming the jury with conflicting advice that it cannot competently evaluate?

Let’s start by just accepting the foregoing statements about juror comprehension truth. Even so, the point is uncompelling and fails to injure reason’s role in this process. Social epistemology deals with when we can justify our beliefs in what others say --- specifically, those who hold themselves out as experts.

The idea is that knowledge (the process itself) transfers and this process accords with reason, even without the recipient understanding how that knowledge came to be:

“If B knows p and B says in a testimonial act that p to A, then, if A recognizes her epistemic dependence on B, A knows p.”

The mutual recognition of an information asymmetry creates a joint commitment and obligation. And this good-faith obligation arises because of the expert holding himself out as such: refer to the “expertise” criterion for epistemic paternalism. Because the listener acknowledges a knowledge gap and is unable to evaluate the expert’s performance based on knowledge quality, the listener may use other means to assess whether the expert has kept his implicit promise.

And this process makes a juror accepting an expert witness’s testimony without understanding it reasonable --- so long as the juror has good reason to believe the expert has upheld his end of the implicit bargain. Consequently, the juror can utilize methods of assessing an expert witness’s credibility while still engaged in a rational thought process.

And in social epistemology there are five main methods --- all justifiable to the extent the individual can utilize them --- for choosing whether to rationally believe an expert has fulfilled his social obligation.

  • Directly or indirectly assessing the expert’s argumentation (indirect is assessing argumentative performance)
  • Seeking out statements from other experts and evaluating which seems the most competent.
  •  Obtaining information regarding an expert’s credentials.
  • Proof by popularity --- if a lot of other experts agree with this expert, then this is evidence that the expert is correct.
  • Evaluating other indicia of trustworthiness or bias.

Two questions we can now answer:

  • Did the jurors understand the expert witness’s testimony, or his parachute, or his steering, or the tracks?

It’s irrelevant.

  • So which part of the train ride inception mattered: was it the daring entrance by parachute, the confident commandeering of the train, the magical train tracks that appeared over the chasm, or the strange whismy of his appearance there with a charming pipe?

All of them mattered.

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