Chances Are (30 page)

“Law,” etymologically, means “that which lies beneath”: the unchanging standard against which mere happenstance is measured. Human events careen into the past, set going by motives we may not even know at the time. Yet when experience is brought to court, it must line up against the shining rule, and the bulgy mass of grievance and retort must be packed into the box of judgment. Achieving this task means answering two probabilistic questions: “Are these facts likely to be true?” and “If they are true, is this hypothesis the most likely one to explain them?”

These are not answered by a basalt obelisk. They are human inquiries, pursued through the intrinsically human capability of speech—witnessing and argument. The first law case on record dates from the Sixth Dynasty of Egypt's Old Kingdom. It concerns (for some things never change) a disputed will; and the judgment required Sebek-hotep, the defendant, to bring three reputable witnesses to swear by the gods that his account of the matter was accurate and his document not a forgery. We see here, at its very beginning, the elements that have remained vital to legal process: testimony, numbers, reputation, and the oath.

These matters absorbed the attention of lawmakers in every tradition: Deuteronomy requires that “One witness shall not rise up against a man for any iniquity . . . at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established.” The Romans preferred a rich witness over a poor one (as less likely to be bribed) and excluded anyone guilty of writing libelous poems. Jewish law forbade testimony from dice players or pigeon fanciers—but also ruled out all confessions, since they were unlikely to be obtained legitimately. People tend to affirm what they have heard others say; rules against hearsay evidence and conjecture appear very early. So does the idea that it is the accuser who must prove the charge, and that this proof, in criminal cases, should be beyond a reasonable doubt. “You found him holding the sword, blood dripping, the murdered man writhing,” says the Talmud; “if that is all, you saw nothing.”

How was proof established? By argument. If you wonder why court proceedings are verbal—with all that repetition, hesitation, digression, and objection—it is because law keeps direct contact with the standards and habits of the ancient world. Life in classical Athens was one long conversation. Good talk flowed in spate throughout the city: smooth and easy in the after-dinner symposia, hard and forceful in the courts, intricate and demanding in the academies. All had one source, essential curiosity; and one goal, to try ideas by argument. The methods were the same when Socrates and his pupils were analyzing the Good in the shadow of a colonnade as when the old man himself was standing on trial for his life.

Legal rhetoric has a bad name, but it is simply a degraded form of that Rhetoric the Greeks defined as the science of public reasoning. Aristotle, who never did things out of order, published his
Rhetoric
before he even began his logical masterwork, the
Prior Analytics
—seen in his terms, logical argument is just the chamber form of rhetoric. “All men are mortal” is not just a statement; it is a form of provisional law, like “all professional burglars re-offend.” To link, as in deductive logic, the actors of here and now to some provisional law is the essence of judicial reasoning: “Socrates is mortal”; “West Side Teddy is a professional burglar.” The syllogisms we discussed in Chapter 1 are really skeletons of legal cases, waiting to be fleshed out with facts and names.

For a work on persuasion, the
Rhetoric
is hard going—but those who plow through it are rewarded by the first explicit treatment of the probable, which Aristotle considered both as the
plausible
and the
likely,
defined as “what usually happens.” You can use it to draw conclusions based on previous experience, as well as to make assumptions about the future based on the past, or expect the more usual based on the unusual. Thus: “He is flushed and his pulse is racing; it is likely he has a fever”; “She has always criticized my clothes; it is likely she will tomorrow”; and “He committed murder without a second thought; it is likely he would also be willing to double-park.”

Arguments from likelihood appear weaker than deductive logic, but sometimes prove stronger, since they are not necessarily
dis
proved by one counterexample. Hence, Aristotle says, judges “ought to decide by considering not merely what
must
be true but also what is
likely
to be true”: this is, indeed, the meaning of “giving a verdict in accordance with one's honest opinion.”

Obviously, this likelihood is open to abuse: a puny man may say, “It is unlikely that I committed this murder,” but then the strong man can say, “It is unlikely that I, who would be so easily suspected, committed this murder”—or, as the poet Agathon pointed out, “We might call it a probability that many improbable things happen to men.” So legal probability could do anything that logical argument does, except stand on its own unaided. Syllogisms are self-evident, but the use of likelihood means that the conclusion resides not in the speaker's words, but in the listener's understanding: that is what makes legal probability a branch of rhetoric.

 

“What usually happens” is a concept that slides all too easily into “what people like us usually do.” Christ's parables employed likelihood in the first sense: good fathers usually forgive their sons, good stewards improve their opportunities. Christ's accusers employed it in the second sense: we are not accustomed to eat with sinners or heal on the Sabbath. When Pontius Pilate asked, “What is Truth?” he was in a courtroom, and—to give this Greek-educated official his due—may well have been pointing out how difficult it is to reconcile conflicting views of probability based on different premises.

Among the Romans, the shared sense of “what usually happens” gained added support from their universal grounding in basic law and well-informed love of rhetorical theater. The law tables were terse, allusive, and rhythmic: the foundation song of the Republic. Schoolchildren were expected to memorize them. Every politician seeking glory had not only to win a military victory against the barbarians, but had also to conduct a successful defense and prosecution. These performances took place in the open forum, before an audience as passionately expert in legal spectacle as its descendants are in opera or soccer: once, when Cicero finished an oration with the quick flick-flack of a double trochee, the whole court erupted in frenzied cheering.

All this—the brilliance, the freedom of judgment, the shared expectations—depended heavily on those two prerequisites for civilization: leisure and self-confidence. By the time Justinian became emperor in 527, neither quality was very evident. Rome was in the hands of the Ostrogoths; plague and riot raged through the remains of Empire. It was not a time to rely on “what usually happens.”

Justinian, like Napoleon, was a determined and ruthless centralizer, and to concentrate power he collected and codified all law. His
Decisions
,
Institutes
,
Digest,
and
Code
—issued in the course of four years—superseded all previous legislation, nullified all other opinion, and founded the entire Western legal tradition. It is to Justinian that we owe our system's uneasy yoking of statute and common law, eternal principles and local exceptions, sword and scales.

 

As the darkness deepened, though, even the simplest laws soon lost their relevance. In the centuries of chaos, where dispute so often led directly to blood feud, there was no point in establishing evidence or pursuing judicial reasoning. Only God could provide proof—instantly and miraculously—in trial by battle, trial by water, and trial by ordeal, where you walked unharmed over red-hot plowshares or swallowed the blessed wafer that catches in the throat of liars. Each side could bring oath-helpers, whose numbers and standing amplified the power of the word. Oh—and in England, they would first put the matter to a jury of your peers. These were not the disinterested jurors of today, but quite the opposite—people who knew all about the accused and the background of the case—and their purpose had less to do with democratic integrity than with getting a decision that would satisfy the village. The results were often unjust, but then injustice was what one expected in this world: when Simon de Montfort led the crusade against the Cathars, he killed everyone he came on, heretic and Catholic alike, confident that God would sort them out to Heaven or Hell as they deserved.

 

Justinian's
Digest
was recovered during that explosive eleventh century which gave us universities, cathedrals, and cities. It was seen, like the surviving works of Aristotle, as a testament from a lost age, to be treated with the respect and minute attention accorded to all holy texts. The University of Bologna, the first Law School, was founded purely to study the
Digest
. One of its early professors, Azo, noticed that not all proofs in Justinian's law were complete: so what should one do with types of evidence that fell short of the high standards necessary to convince the court? What, for instance, if one had the testimony of only one witness, or an unwitnessed but credible document? Azo called these “half-proofs” and suggested that two halves could make a whole. His successors created an entire new legal arithmetic for building cases from probabilistic components: suspicion, various sorts of presumption, indication, argument, support, and conjecture.

Each element of the new construct was derived from a Roman legacy, but the spirit of it—its subtlety, proliferation of terms, and artificiality—was entirely medieval. Corals of interpretation grew over the rock of law, and their effect was to move questions of likelihood and credibility from rhetoric into textual analysis. It was no longer the audience in the forum that would decide if an interpretation was likely; it was the skilled professional with a degree. Justinian had intended to give the world law; unintentionally, he gave it lawyers.

Law is eternal truth, but to fit the facts of a changing world into the ancient form of statute meant framing what actually happened in terms of what never happens. This was the doctrine of “legal fiction”: making the actors in modern cases play their parts under the names and in the costumes of long-dead characters. For legal purposes, all ducks were “beasts,” all civil cases in England were about an assault in Middlesex, and all property disputes revolved around the rights of John Doe and Richard Roe, fictional men to whom the owners had notionally leased their land. Some civil cases pretended to be criminal: in order to get his case into the royal court, one fourteenth-century claimant had to assert that the vintner from whom he had bought bad wine had watered it down “against the peace of the king, to wit with bows and arrows”—on the face of it, a method more likely to spike the drink.

One fiction, though, was the saving of the British and American legal systems: the common law. This asserts an unwritten but supreme tradition—what has always happened—glimpsed only in the mirror of past judgments. There can be nothing new in common law—yet there is always something new to find in it as the world changes and judges inquire more deeply. Code-based law hurtled inevitably toward the road-block of contradiction, but the common law offered a network of country lanes leading in a leisurely circuit around any obstacle.

Under Justinian, you could decide by the
Code
—but code and reality were now too far apart. In the Middle Ages, you could look to Authority—but there were now so many opinions on each side that they canceled each other out. By Rabelais' time, matters had gone beyond confusion to absurdity: his character Judge Bridlegoose claimed that the only perfect, impartial method of deciding a case was . . . to throw dice.

 

Rabelais was trained as a lawyer; so was Fermat. Cardano and Pascal were sons of lawyers. Several Bernoullis studied law before mathematics tempted them away. The originators of probability had a clear sense of how maddeningly intractable law is to reason. Now they hoped this new method, so successful in disputes about dice and stakes, could extend to Justice.

Leibniz was another mathematician who began by studying law. When he came up with the basic notation still used in probability—0 for the impossible, 1 for the certain, and all the fractions in between for the varyingly probable—his intention had been to use this to measure legal validity: a more subtle and continuous version of Azo of Bologna's arithmetic of half-proofs. Leibniz was sure that it was possible not only to determine numerical values for the probability of statements, but to combine these into a calculus of inference, mechanically “estimating grades of probability and the status of proofs, presumptions, conjectures, and indices.” But he reckoned without Bernoulli, who simply asked Leibniz what legal examples he could think of that reveal their intrinsic probabilities after the fact, as mortality tables reveal the average length of life. Leibniz came up with nothing; the plan for a judicial calculator went the same way as his attempt to reconcile Protestants with Catholics.

Bernoulli's point was valid: statistics and probability are not the same. Even perfectly accurate and impartial records of crime will tell you nothing about
this
accused in this particular case. Nor was his the only valid objection to applying a calculus of probabilities to the law. Can you, for example, repeat a murder to reveal the weight of its evidence, as you would repeat the draw from an urn? Would you be willing to try the same suspect 25,550 times so as to be 99.99 percent certain that your verdict reflected the truth? Say two independent witnesses tell the same story but each is only half-credible; shouldn't you (since they are independent) multiply their probabilities? But if you do, you turn two half-proofs into one quarter-proof. This doesn't sound like the way to purge law of its ambiguities.