Haack Attack on Legal Probabilism

Last year, Professor Susan Haack presented a lecture on “legal probabilism,” at a conference on Standards of Proof and Scientific Evidence, held at the University of Girona, in Spain.  The lecture can be viewed on-line, and a manuscript of Haack’s paper is available , as well.  Susan Haack, “Legal Probabilism:  An Epistemological Dissent” (2011)(cited here as “Haack”).   Professor Haack has franked her paper as a draft, with an admonition “do not cite without permission,” an imperative that has no moral or legal force.  Her imperative certainly has no epistemic warrant.  We will ignore it.

As I have noted previously, here and there, Professor Haack is a Professor of philosophy and of law, at the University of Miami, Florida.  She has written widely on the philosophy of science, in the spirit of Peirce’s pragmatism.  Despite her frequent untutored judgments about legal matters, much of what she has written is a useful corrective to formalistic writings on “the scientific method,” and are worthy of study by lawyers interested in the intersection of science and the law.

The video of Professor Haack’s presentation is worth watching to get an idea of how ad hominem her style is.  I won’t repeat her aspersions and pejorative comments here.  They are not in her paper, and I will take her paper, which she posted online, as the expression of her mature thinking.

Invoking Lord Russell and Richard von Mises, Haack criticizes the reduction of epistemology to a calculus of probability.  Russell, for instance, cautioned against confusing the credibility of a claim with the probability that the claim is true:

“[I]t is clear that some things are almost certain, while others are matters of hazardous conjecture. For a rational man, there is a scale of doubtfulness, from simple logical and arithmetical propositions and perceptive judgments, at one end, to such questions as what language the Myceneans spoke or “what song the Sirens sang” at the other … , [T]he rational man, who attaches to each proposition the right degree of credibility, will be guided by the mathematical theory of probability when it is applicable . … The concept ‘degree of credibility’, however, is applicable much more widely than that of mathematical probability.”‘

Bertrand Russell, Human Knowledge, Its Scope and Limits 381 (N.Y. 1948)(quoted in Haack, supra, at 1).   Haack argues that ordinary language is beguiling.  We use “probably” to hedge our commitment to the truth of a prediction or a proposition of fact.  We insert the adverb “probably” to recognize that our statement might turn out false, although we have no idea of how likely, and no way of quantifying the probability of error.  Thus,

“[w]e commonly use the language of probability or likelihood when we talk about the credibility or warrant of a claim-about how likely is it, given this evidence, that the claim is true, or, unconditionally, about how probable the claim is.”

Haack at 14.

Epistemology is the “thing,” and psychology, not.  Haack admits that legal language is inconsistent:  sometimes the law appears to embrace psychological states of mind as relevant criteria for decisions; sometimes the law is expressly looking at epistemic warrant for the truth of claim.  Flipping the philosophical bird to Derrida and Feyerabend, Haack argues that trials are searches for the truth, and that our notions of substantial justice require replacement of psychological standards of proof, to the extent that they are merely subjective and non-epistemic, with a clear theory of epistemic warrant.  Haack at 6 (citing Tehan v. United States, 383 U.S. 406,416 (1966)(“the purpose of a trial is to determine the truth”); id. at 7 (citing In re Winship, 397 U.S. 358, 368, 370 (1970) (Harlan, J. concurring)(the standard of proof is meant to “instruct the factfinder concerning the degree of confidence our society thinks he should have in the correctness of factual conclusions for a particular type of adjudication.)

Haack points out that there are instances where evidence seems to matter more than subjective state of mind, although the law sometimes equivocates.  She cautions us that “we shouldn’t simply assume, just because the word “probable” or “probability” occurs in legal contexts, that we are dealing with mathematical, rather than epistemological, probabilities.  Haack at 16.  (citing and quoting Thomas Starkie, et al., A Practical Treatise of the Law of Evidence and Digest of Proofs in Civil and Criminal Proceedings vol. I, 579 (Philadelphia 1842)(“That … moral probabilities … could ever be represented by numbers … and thus be subject to numerical analysis,” … “cannot but be regarded as visionary and chimerical.”)  Thus the criminal standard, “beyond a reasonable doubt” seems to be about state of mind, but it is described, at least some of the time, as about the quality and strength of the evidence needed to attain such a state of mind.  The standards of “preponderance of the evidence” and “clear and convincing evidence,” on the other hand, appear to be directly related to the strength of the evidentiary display offered by the party with the burden of proof.

An example that Haack might have used, but did not, is the requirement that an expert witness express an opinion to a “reasonable degree of medical or scientific certainty.”  The law is not particularly concerned about the psychological state of certainty possessed by the witness:  the witness may be a dogmatist with absolute certainty but no epistemic warrant; and that simply will not do.

Of course, the preponderance standard is alternatively expressed as the burden to show the disputed fact is “more likely than not” correct, and that brings us back to explicit probabilisms in the law.  Haack’s argument would be bolstered by acknowledging the work of Professor Kahnemann, who makes the interesting point, at several places, that experts, or for that matter anyone making decisions, are not necessarily expert at determining their level of certainty.  Can someone really say that they believe one set of claims have been shown to be 50.1%, and have an intelligent discussion with another person, who adamantly believes that the claims have been shown to 49.9% true.  Do they resolve their differences by splitting the differences?  Unless we are dealing with an explicit set of frequencies or proportions, the language of probability is metaphorical.

Haack appropriates the term warrant for her epistemiologic theory, but the use seems much older and not novel with Haack.  In any event, Haack sets out her theory of “warrants”:

“(i) How supportive the evidence is; analogue: how well a crossword entry fits with the clue and intersecting completed entries. Evidence may be supportive (positive, favorable), undermining (negative, unfavorable), or neutral (irrelevant) with respect to some conclusion.

(ii) How secure the reasons are, independent of the claim in question; analogue:  how reasonable the competed intersecting entries are, independent of the entry in question. The better the independent security of positive reasons, the more warranted the conclusion, but the better the independent security of negative reasons, the less warranted the conclusion.

(iii) How comprehensive the evidence is, i.e., how much of the relevant evidence it includes; analogue: how much of the crossword has been completed. More comprehensive evidence gives more warrant to a conclusion than less comprehensive evidence does iff the additional evidence is at least as favorable as the rest.”

Haack at 18 (internal citation omitted).  According to Haack, the calculus of probabilities does not help in computing degrees of epistemic warrant.  Id. at 20. Her reasons are noteworthy:

  • “since quality of evidence has several distinct dimensions (supportiveness, independent security, comprehensiveness), and there is no way to rank relative success and failure across these different factors, there is no guarantee even of a linear ordering of degrees of warrant;
  • while the probability of p and the probability of not-p must add up to 1, when there is no evidence, or only very weak evidence, either way, neither p nor not-p may be warranted to any degree; and
  • while the probability of p and q (for independent p and q) is the product of the two, and hence, unless both are 1, less than the probability of either, the warrant of a conjunction may be higher than the warrant of its components”

Id. at 20-21.  The third bullet appears to have been a misfire.  If we were to use Bayes’ theorem, the two pieces of evidence would require sequential adjustments to our posterior odds or probability; we would not multiply the two probabilities directly.

Haack’s attack on legal probabilism blinds her to the reality that sometimes all there is in a legal case is probabilistic evidence.  For instance, in the litigation over claims that asbestos causes colorectal cancer, plaintiffs had only a relative risk statistic to support their desired inference that asbestos had caused their colorectal cancers.  There was no other evidence.  (On general causation, the animal studies failed to find colorectal cancer from asbestos ingestion, and the “weight of evidence” was against an association in any event.)  Nonetheless, Haack cites one case as a triumph of her anti-probabilistic viewpoint:

“Here I am deliberately echoing the words of the Supreme Court of New Jersey in Landrigan, rejecting the idea that epidemiological evidence of a doubling of risk is sufficient to establish specific causation in a toxic-tort case: ‘a relative risk of 2.0 is not so much a password to a finding of causation as one piece of evidence among many’.114 This gets the key epistemological point right.”

Landrigan v. Celotex Corp., 127 N.J. 405, 419, 605 A.2d 1079 (1992).  Well, not really.  Had Haack read the Landrigan decision, including the lower courts’ opinions, she would be aware that there were no other pieces of evidence.  There were no biomarkers, no “fingerprints” of causation; no evidence of Mr. Landrigan’s individual, special vulnerability.  The case went up to the New Jersey Supreme Court, along with a companion case, as a result of directed verdicts.  Caterinicchio v. Pittsburgh Corning Corp., 127 N.J. 428, 605 A.2d 1092 (1992). The plaintiffs had put in their cases and rested; the trial courts were required to assume that the facts were as presented by the plaintiffs.  All the plaintiffs had offered, however, of any possible relevance, was a relative risk statistic.

Haack’s fervent anti-probabilism obscures the utility of probability concepts, especially when probabilities are all we have.   In another jarring example, Haack seems to equate any use of Bayes’ theorem, or any legal analysis that invokes an assessment of probability, with misguided “legal probabilism.”  For instance, Haack writes:

“Mr. Raymond Easton was arrested for a robbery on the basis of a DNA “cold hit”; statistically, the probability was very low that the match between Mr. Easton’s DNA (on file after an arrest for domestic violence) and DNA found at the crime scene was random. But Mr. Easton, who suffered from Parkinson’s disease, was too weak to dress himself or walk more than a few yards-let alone to drive to the crime scene, or to commit the crime.”

Haack at 37 (internal citation omitted).  Bayes’ Theorem, with its requirement of inclusion of a base rate, or prior probability, in the complete analysis provides the complete answer to Haack’s misguided error about DNA cold hits.


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