Plato and AristotleModern society has two means by which it assesses truth or falsity: science and law. Just as Einstein recognized "there is no logical path to the [elemental laws of the universe]; only intuition, resting on sympathetic understanding of experience, can reach them," Holmes taught "the life of the law has not been logic; it has been experience."

Scientists and lawyers have learned to value pragmatic experimentation over logical deduction; call it the victory of Aristotle over Plato. (Scientists and lawyers also share a love of semicolons.)

But they don’t always reach the same conclusions, particularly not on matters of the mind.

Consider the the Second Circuit’s forty-four year-old opinion in United States v. Freeman, 357 F.2d 606 (2nd Cir. 1966) railing against the M’Naghten Rule, which by then had thrived for a century, despite complaints from the scientific and medical community:

Prominent psychiatrists have expressed their frustration when confronted with such requirements. Echoing such complaints, Edward de Grazia has asked, "How [does one] translate `psychosis’ or `psychopathy’ or `dementia praecox’ or even `sociopathy’ or `mental disorder’ or `neurotic character disorder’ or `mental illness’ into a psychiatric judgment of whether the accused knew `right’ from `wrong.’" In stronger and more vivid terms, Dr. Lawrence Kolb, Director of the New York Psychiatric Institute, Professor and Chairman of the Department of Psychiatry at Columbia University and Director of the Psychiatric Service at Presbyterian Hospital, expressed a similar viewpoint when he declared that "answers supplied by a psychiatrist in regard to questions of rightness or wrongness of an act or `knowing’ its nature constitute a professional perjury."

Psychiatrists are not alone in their recognition of the unreality of M’Naghten. As long ago as 1930, Mr. Justice Cardozo observed that "everyone contends that the present definition of insanity has little relation to the truths of mental life." And Mr. Justice Frankfurter, as a witness before the Royal Commission on Capital Punishment, declared with his usual fervor: "I do not see why the rules of law should be arrested at the state of psychological knowledge of the time when they were formulated. * * * I think the M’Naghten Rules are in large measure shams. That is a very strong word, but I think the M’Naghten Rules are very difficult for conscientious people and not difficult enough for people who say, `We’ll just juggle them.’"

Even then, the courts knew the rule was scientific anathema, and yet it doggedly held on — a generation after Freeman it remained the "central ingredient" of the insanity defense in the Second Circuit, and it remains the basis for the law of criminal insanity today. United States v. Hansen, 701 F. 2d 1078 (2nd Cir. 1983); US v. Garcia, 94 F.3d 57 (2nd Cir. 1996).

Last week, The Experimental Philosophy blog updated us on the latest in this ages-old dispute:

The MacArthur Law and Neuroscience Project (along with the SAGE Center at UCSB) recently published A Judge’s Guide to Neuroscience:  A Concise Introduction

The introduction to the Guide is written by no less than the indefatigable Judge Jed Rakoff, who sought out from his colleagues the neuroscience questions they wanted answered, boiling those requests down to:

  • What is cognitive neuroscience?
  • What is an fMRI?
  • Can neuroscience identify lies?
  • What is neurogenetics?
  • Can neuroscience identify pain?
  • Does neuroscience give us new insights into criminal responsibility?
  • Does neuroscience give us new insights into drug addiction?
  • Can neuroscience identify psychopaths?
  • Has neuroscience already appeared in the courtroom?
  • How is neuroscience likely to impact law in the near future?
  • How is neuroscience likely to impact the law in the long run?

The answers run the gamut from it’s complicated, to sort of, to no; there’s not a single "yes" to be found.

In short, though cognitive neuroscience has much to offer in understanding the function of the brain, it cannot yet reliably provide information useful to the adjudication of civil and criminal disputes, except in rare instances.

In a way, that’s refreshing to hear.

Pseudoscience is, and always has been, endemic to the law. Even entirely reputable scientific fields can be abused and misused by unscrupulous "experts" serving as witnesses, or by misguided lawyers and judges unaware of their own ignorance. A little bit of knowledge is a dangerous thing, particularly when you’re duty-bound to apply it.

The problem is particularly acute when, as with cognitive neuroscience, the science in question purports to tell us the inner workings of the parties’ or witnesses’ minds. In discussing polygraphs — themselves often accused of being little more than pseudoscience — the Supreme Court described the problem:

A fundamental premise of our criminal trial system is that "the jury is the lie detector." United States v. Barnard, 490 F. 2d 907, 912 (CA9 1973) (emphasis added), cert. denied, 416 U. S. 959 (1974). Determining the weight and credibility of witness testimony, therefore, has long been held to be the "part of every case [that] belongs to the jury, who are presumed to be fitted for it by their natural intelligence and their practical knowledge of men and the ways of men." Aetna Life Ins. Co. v. Ward, 140 U. S. 76, 88 (1891).

By its very nature, polygraph evidence may diminish the jury’s role in making credibility determinations. The common form of polygraph test measures a variety of physiological responses to a set of questions asked by the examiner, who then interprets these physiological correlates of anxiety and offers an opinion to the jury about whether the witness—often, as in this case, the accused——was deceptive in answering questions about the very matters at issue in the trial. See 1 McCormick § 206. Unlike other expert witnesses who testify about factual matters outside the jurors’ knowledge, such as the analysis of fingerprints, ballistics, or DNA found at a crime scene, a polygraph expert can supply the jury only with another opinion, in addition to its own, about whether the witness was telling the truth. Jurisdictions, in promulgating rules of evidence, may legitimately be concerned about the risk that juries will give excessive weight to the opinions of a polygrapher, clothed as they are in scientific expertise and at times offering, as in respondent’s case, a conclusion about the ultimate issue in the trial.

United States v. Scheffer, 523 U.S. 303 (1998). So it goes with cognitive neuroscience. It’s one thing when a forensic expert testifies about the presence of gunpowder on a jacket, and quite another when a neuroscientist purports to explain how he knows the defendant is lying about where the gunpowder came from.

Which is why I’m so grateful for the scientists’ candor in describing the limitations of their field. Far from being a disappointment, the negative or tentative answers given by the neuroscientists will hopefully keep snake-oil and pseudoscience out of the courtroom while the field itself continues to grow.

As fascinating as neuroscience is, then, the experience of the law still suggests relying on that most effective of lie detectors: the impartial jury.