“The expert in a patent case can testify to the underlying facts in support of an opinion, just as experts in other types of cases can testify to underlying facts. An expert may talk about what is or is not disclosed in the prior art, for example, or how words are used in the technical area, or how a device operates. But the expert may not go the extra step and say that a claimed invention is obvious.”

When obviousness of a patent claim is at issue, some experts may opine along these lines: “Therefore, the subject matter of claim 1 would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art.”

Whether such is common practice or not, testimony of this sort ought not to be allowed. Such testimony should be objected to and stricken as irrelevant. In cases involving a jury, a motion in limine ought to be used to prevent such testimony from coming before a jury.

The Roles of Experts

Experts are fact witnesses that are, like all fact and other witnesses, allowed to testify to what they saw, what they heard, and what they did. Unlike other witnesses, however, expert witnesses are further allowed to express opinions within the fields of their expertise. Experts’ expertise comes from having specialized knowledge, education, training, or experience.

Regardless of their fields, experts’ expertise does not extend to questions of law. No witness, not even an expert, can render a legal opinion.

This principle of evidence finds application throughout the law. There are numerous civil and criminal cases in which experts were allowed to opine about the significance of various facts but were not allowed to opine that there was a legal violation, for example, or that a legal standard was satisfied. Fed. R. Evid. 702 treats experts as witnesses allowed to give opinions within their areas of expertise. Opinions about the law, however, are not specifically allowed by this rule. Although Fed. R. Evid. 704(a) says “An opinion is not objectionable just because it embraces an ultimate issue,” this does not mean that testimony about an ultimate issue of law is permitted.

There is some case authority permitting experts to testify on “ultimate” issues that involve legal standards. The touchstone for admissibility, however, is whether the testimony is helpful to the decision-maker, whether it be judge or jury. See the Notes of Advisory Committee to Fed. R. Evid. 704.

There are numerous reasons for disallowing expert testimony on legal issues.

1. Expert Testimony Is Unnecessary.

Before any judicial or quasi-judicial tribunal, the law is presented to the legal decision-maker not from the witness stand but from counsel table. Briefs, motions, oral arguments, proposed jury instructions, and other advocacy vehicles are available for helping the judge identify and evaluate a legal issue. Admitting sworn testimony on a legal issue of American law is unnecessary.

2. Many Experts Are Not Legal Experts, Anyway.

Many experts have no legal training at all, so testifying to a legal issue is beyond the range of the expert’s expertise.

3. The Legal Decision-Maker Has A Monopoly as To the Law.

Questions of law are to be determined only by a tribunal, such as an appellate court, or a trial court, or the Patent Trial and Appeal Board. The tribunal, and only the tribunal, is empowered to address legal issues.

In a district courtroom, for example, the only person in the room empowered to determine legal questions is the person who sits on the bench.

Advocates cannot say what the law is. Advocates may argue as to what rules ought to apply or whether the law requires something or whether a legal standard is met, or whether a particular outcome ought to be reached; but their arguments are in no way binding upon the legal decision-maker.

A jury cannot say what the law is. In a jury trial, the jury must follow the law as instructed by the judge, and typically jurors take an oath or affirmation to follow the judge’s instructions.

An expert cannot say what the law is. If an expert were to testify to a legal question before a jury, then there would be a risk that the expert would misstate the law or otherwise interfere with the judge’s instructions. There is an unavoidable prospect for confusion where an expert espouses one standard and the judge instructs on another.

The prospect for confusion is not limited to jury trials. Even in the case of a bench trial, expert testimony about a legal question could lead to confusion or misapprehension of the proper legal standards. The same prospect for confusion also exists in a hearing before an agency.

It is sometimes said that the problem with expert opinions reciting legal conclusions is that they infringe upon the function of the jury. Actually, the problem with expert opinions on issues of law is even more basic than that.

Such opinions are, quite simply, not relevant.

Obviousness Is an Issue of Law

Obviousness is an issue of law. E.g., In re Magnum Oil Tools Int’l, Ltd., 829 F.3d 1364, 1373 (Fed. Cir. 2016). As a matter of principles of evidence, experts are not allowed to testify as to issues of law. There is no exception to this principle in patent law. Accordingly, an expert ought not to be allowed to express an opinion as to whether something is obvious or not.

To be sure, the expert in a patent case can testify to the underlying facts in support of an opinion, just as experts in other types of cases can testify to underlying facts. An expert may talk about what is or is not disclosed in the prior art, for example, or how words are used in the technical area, or how a device operates. But the expert may not go the extra step and say that a claimed invention is obvious. To do so would be to express an opinion on a legal issue.

The Millennium Case

The case of Millennium Pharm., Inc. v. Sandoz Inc., 862 F.3d 1356 (Fed. Cir. 2017), shows that expert testimony on obviousness is irrelevant. The Millennium case also demonstrates the pitfalls of what happens when expert testimony improperly strays into such legal questions. (The Millennium case is also notable for its discussion of inherency as it relates to obviousness.)

The Millennium case involved a pharmaceutical patent that had been challenged in district court as obvious, and the district court invalidated the claims in question on obviousness grounds.

The Federal Circuit determined there was a legal error in the district court’s determination. Without going into the highly technical details of what was missing, there was no evidence supporting motivation to make the claimed invention, nor any indication in the prior art that the invention could be made.

In short, the prior art had at least one evidentiary “gap” in it, and the gap was fatal to a determination of obviousness, as a matter of law.

And yet, there was considerable testimony in the record that the compound was indeed “obvious.” In particular, expert testimony had been admitted——from not one but from several experts——that the compound was obvious in view of the prior art.

The district court gave the expert testimony considerable weight and agreed that the compound was obvious.

On appeal, the Federal Circuit had this to say about the experts’ testimony: “None of the experts presented by the many defendants stated that they were aware of prior art to fill any of the gaps in teaching or suggestion of the [patented] product——although they variously opined that this long-sought discovery was obvious.”

Arguments were made by counsel that the prior art did show those things that were thought to be missing. Arguments of counsel are not evidence, of course; and when pressed, the experts themselves were unable to identify where the references disclosed those missing things.

In the end, the Federal Circuit gave these expert opinions on the issue of obviousness no weight or deference at all. The opinions made no difference in the outcome.

The expert opinions on the issue of obviousness were, quite simply, irrelevant.

What Does the Millennium Case Mean?

The Millennium case highlights the evidentiary significance of expert testimony in several respects.

1. Expert Testimony Is Not Prior Art.

At the risk of venturing into tautology, only prior art is prior art. Experts cannot in general pass off their present-day opinions as time-of-filing (or time-of-invention) prior art.

2. Expert Opinions May Not Fill in Evidentiary Gaps.

Of course, the prior art that forms the bases for an expert’s opinions is prior art and is always fair game for a challenge. In the Millennium case, the prior art was challenged, and there were gaps to be found in it. It was clear error for the district court to conclude that there was obviousness, with such gaps present in the evidence. The experts opined that, in spite of the gaps, there was obviousness anyway. The Federal Circuit determined that this expert testimony did not matter one bit, effectively saying that expert testimony cannot fill in gaps in the prior art.

In other contexts, the Federal Circuit has recognized the principle that technical expertise is not a substitute for prior art evidence. See, e.g., In re Lee, 277 F.3d 1338, 1344-45 (Fed. Cir. 2002) (agency expertise is not evidence, and cannot serve as a substitute for evidence). The Millennium case suggests that a similar principle applies to expertise of outside experts as well, and that this principle applies in adversarial proceedings.

3. The Potential for Confusion Is Quite Real.

Expert testimony about obviousness could lead to confusion or misapprehension of the proper legal standards, and in the Millennium case, that very thing seems to have happened.

Indeed, the expert testimony apparently had a profound effect upon the district court. The district court’s written decision made special note of one of the experts, Dr. Repta, who opined how a person of ordinary skill in the art “would have found the claims obvious based on the art described.” The judge was explicit in his reliance upon this expert: “The court finds that the testimony of Dr. Repta is persuasive and supported by the evidence.”

The Federal Circuit’s Millennium opinion, however, demonstrates that the experts did not understand the proper legal standards, because they concluded that the claimed invention could still be obvious in spite of fatal gaps in the prior art evidence. This was not a factual error; it was a legal error. The experts had testified that obviousness was present, when as a matter of law, it was not present; and the district court made a reversible error by adopting those experts’ conclusions.

Notably, the law of the Third Circuit, in which the Millennium case was tried, held that no witness may testify to a legal conclusion. E.g., Berckeley Inv. Grp., Ltd. v. Colkitt, 455 F.3d 195, 217 (3d Cir. 2006) (“an expert witness is prohibited from rendering a legal opinion”). The district court allowed the testimony anyway (possibly over no objection) and made a legal error by relying upon it.

4. Expert Opinions About Obviousness Carry No Weight.

In the Millennium case, expert opinions as to what “obvious” means, or what is or is not obvious, carried no weight.

Irrelevant Evidence Is to Be Excluded.

Under the Federal Rules of Evidence, irrelevant evidence is not permitted and may not be relied upon as a basis for a conclusion. Expert opinion as to obviousness, being irrelevant and therefore improper, ought to be excluded from an evidentiary record made in a courtroom.

Expert opinion on obviousness also ought to be excluded from quasi-judicial proceedings before the USPTO, such as cases of inter partes review. It is true that the agency’s rules of evidence are not identical to those of the federal courts; but it does not follow that the agency is bound by no rules of evidence at all.

In a case before the agency, irrelevant subject matter must be excluded. The Administrative Procedure Act, 5 U.S.C. § 556(d), addresses that evidentiary rule: “the agency as a matter of policy shall provide for the exclusion of irrelevant, immaterial, or unduly repetitious evidence.”

If experts are known habitually to opine on legal questions of obviousness, it may be time for that practice to come to an end.

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