Russell’s right. The mathematical calculus of probabilities is perfectly fine in its place; but that place is a limited one. In particular, this mathematical calculus sheds little or no light on the crucial concept Russell calls “rational credibility,” and I call “warrant.” One consequence, as I shall argue here, is that we can’t look to probability theory for an understanding of degrees and standards of proof in the law, but must look, instead, to an older and less formal branch of inquiry: epistemology.

After Mrs. Daubert had taken Bendectin for morning-sickness in pregnancy, her son Jason was born with severe birth defects. Believing that Bendectin was the cause, in 1989 the Dauberts brought suit against the manufacturers of the drug, Merrell Dow Pharmaceuticals. At trial, however, the court excluded the expert witnesses the Dauberts had proffered to testify on the question of causation, on the grounds that the consensus in the relevant scientific community was that Bendectin does not cause birth defects. With the plaintiffs’ causation experts excluded, there was no case to answer, and the trial court granted summary judgment in favor of Merrell Dow; the appeals court affirmed.

Is truth in the law just plain truth–or is it something sui generis? Is a trial a search for truth–or is it something more, or something less, than that? Do the adversarial procedures of common-law systems promote factually sound verdicts? Do legal rules excluding relevant testimony enable the accurate determination of factual issues, or impede it? What bearing, if any, does the mathematical calculus of probabilities have on the degrees and standards of proof invoked in the law? What role can statistical evidence appropriately play in legal proof? How do the argument and counter-argument of adversarial proceedings differ from what scientists do as they seek out, sift, and weigh evidence? How can courts best handle the scientific testimony on which they now so often rely, and how are they to distinguish genuine science from pretenders–or reliable scientific testimony from unreliable hokum?

The dozen interdisciplinary essays collected here take up a whole nexus of such questions about science, proof, and truth in the law, bringing my work in epistemology and philosophy of science (and, from time to time, my work in philosophy of logic and language, metaphysics, etc.) to bear both on general questions about legal standards of proof and the relative merits of common-law and civil-law approaches to the handling of evidence, and on specific questions about the role of scientific testimony in legal proceedings. A key theme of my epistemology is that the structure of evidence can be understood by analogy with a crossword puzzle; and, just as this would lead you to expect, the arguments of these essays ramify, interlock, and loop up and back.

A PRAGMATIST PREAMBLE: HOW LEGAL CONCEPTS EVOLVE

This paper may not be what you were expecting; at least, if you were anticipating that I would come up with a new analysis of the concept of causation that I could apply in legal contexts, or even with a new critique of Hart and Honoré’s ideas, or a new defense of them, I shall have to disappoint you. Why so?–not because I have tried, but failed, to contribute something to this analytic genre of legal philosophy; rather, because I’m inclined to think it’s more productive to tackle questions about causation, risk, and responsibility in the law in a somewhat different way, better suited to highlighting two facts that seem, at least where the common law is concerned, undeniable: first, that legal concepts generally diverge, in greater or lesser degree, from the everyday concepts in which they have their roots; and second, as Holmes emphasized, that legal concepts aren’t fixed and static, but gradually shift and evolve as social values and priorities change, as new discoveries are made, and as new technology is introduced.

GETTING STARTED

There wasn’t much to be said for the miserable weeks after hurricanes Katrina and Wilma–except, perhaps, that all those hours spent sweating in the dark prompted some vivid thoughts about what life must have been like before electric light and power was available at the flick of a switch, and renewed my appreciation of the countless ways in which science now so thoroughly permeates modern life–including the legal system.

This paper focuses on causation evidence in toxic-tort litigation, and makes two main arguments, the first epistemological and the second legal. The epistemological argument is that, under certain conditions, a congeries of evidence warrants a conclusion to a higher degree than any of its components alone would do; the legal argument, interlocking with this, is that our evidence law encourages a kind of atomism that can actually impede the process of arriving at the conclusion most warranted by the evidence–an atomism the effects of which have been especially salient to causation evidence in toxic-tort cases.

§1 will set the stage by looking at two cases where the epistemological issue to be tackled here came explicitly to courts’ attention; §2 will develop the epistemological argument, first in a general form, and then as it applies to the kinds of causation evidence typically encountered in toxic-tort litigation; §3 will rely on this account to answer some of the epistemological questions about causation evidence that have been at issue in such cases; and §4 will develop the legal argument, showing that, ironically enough, Daubert’s requirement that proffered expert testimony is admissible only if it is reliable may sometimes stand in the way of an adequate assessment of the reliability of causation evidence.

Even today, more than four centuries later, Bacon’s complaint still resonates. Now, as then, the writings of philosophers—even of philosophers of law, who might be expected to be a little more grounded in the real world—all too often “give little light, because they are so high.” I will try to buck this trend by showing you that epistemological ideas really can illuminate real-life legal issues.

IDENTIFYING EPISTEMOLOGICAL ISSUES IN THE LAW

Every legal system needs, somehow, to determine the truth of factual questions. At one time, courts in England and continental Europe relied on in-court tests—“proof” in the old meaning of the English word (a meaning that still survives in descriptions of liquor as “80% proof,” and in the old proverb “the proof of the pudding is in the eating”). In trial by oath, a defendant would be asked to swear on the testament or on a reliquary that he was innocent, and “oath-helpers” or “con-jurors” might be called to swear that his oath wasn’t foresworn; in trial by ordeal, a defendant might be asked, e.g., to pick up a ring from the bottom of a cauldron of boiling water, and his arm would later be checked to determine whether it had healed cleanly or had festered—which supposedly showed that he was guilty; in trial by combat, the two parties to a case would literally fight it out.

Truth is, at its core, quite a simple concept. At the same time, however, it is a concept mired in philosophical confusions. Moreover, on many questions the truth is complicated and subtle–hard to articulate, and difficult to discriminate from plausible falsehoods. And all this, as we shall see, is especially true of truth in the law.

The first step will be to clarify the distinction between truth (the property or phenomenon of being true) and truths (particular true claims), and to then to argue for my first thesis: that, though some propositions are true only at a given place or time, or are vague, or are only partially true, or, etc., truth itself isn’t relative, doesn’t come in degrees, and doesn’t decompose into parts, etc. (§1). The next will be to develop an approach to the understanding of truth along the lines of F. P. Ramsey’s, which will lead to my second thesis: that whatever the subject-matter of the proposition concerned, what it means to say that a proposition is true is the same–that it is the proposition that p, and p (§2). After that, I will explore the (deceptively simple-seeming) distinction between factual and legal truths, and argue for my third thesis: that legal truths, specifically truths about legal provisions, are a special sub-class of truths about social institutions, and make sense only relative to a jurisdiction and a time (§3).