The requirement that a jury in a criminal case reach a unanimous decision became generally established in England during the fourteenth century—about the same time that juries came to be composed of twelve persons. Unanimity began to be generally required for jury verdicts in the American colonies in the eighteenth century. The unanimity requirement as commonly applied means that all the members of the jury must agree upon the verdict—whether for conviction or acquittal. If any of the jurors fail to agree, the jury is "hung"—that is, unable to reach a verdict. Under well-established doctrine, after a hung jury the defendant may be retried.
In a series of cases dating back to the end of the nineteenth century, the Supreme Court has assumed that under the Sixth Amendment the verdict of a criminal jury in the federal courts must be unanimous. This assumption has not been tested, however, for there is no provision for less than unanimous criminal verdicts in the federal courts. The decision in duncan v. louisiana (1968) opened the way for the Court to consider the constitutionality of efforts made by many states to change elements in the common law jury system. Duncan ruled that the fourteenth amendment protected the right to trial by jury in state courts according to the same standards applied under the Sixth Amendment.
To understand the Court's subsequent decisions regarding jury unanimity, it is necessary also to consider its related decisions on jury size. The Court in williams v. florida (1970) upheld the use of six-person juries for serious criminal cases. The question whether state criminal juries must reach unanimous verdicts was presented for the first time in 1972 in two companion cases, apodaca v. oregon and johnson v. louisiana. In Apodaca, the constitutionality of 10–2 verdicts was sustained under the Sixth and Fourteenth Amendments. In Johnson, 9–3 verdicts were upheld under the Fourteenth Amendment alone. In Apodaca, a state case, five Justices (one concurring Justice and four dissenters) also expressed the view that the Sixth Amendment required unanimity in federal criminal trials.
In ballew v. georgia (1978) the Court rendered its second size-of-jury decision, holding five-person juries to be unconstitutional. Thus, by the time the Court considered the issue in burch v. louisiana (1979), it had upheld six-person juries, sustained the constitutionality of 10–2 and 9–3 majority verdicts, and held five-person juries to be unconstitutional. In Burch, the Court held that conviction by a 5–1 vote of a six-person jury violated the constitutional right to trial by jury.
The Court has not in modern times decided whether the seventh amendment requires unanimity in federal civil trials. It can be argued that it so held in two early cases, American Publishing Company v. Fisher (1897) and Springville v. Thomas (1897), but the Court's nonunanimous verdict decisions in state criminal cases and its decision in Colgrove v. Battin (1973) that six-person juries are constitutional in federal civil trials, arguably have undermined those early decisions.
In addressing the unanimity issue in Apodaca and Johnson, the Court relied heavily on the analysis used in the first size-of-jury case, Williams v. Florida, and applied the same functional approach relating the size of the jury to the purposes of a jury trial. From a functional perspective, the unanimity issue has much in common with but is not identical to the jury size question. For example, both involve concerns that juries represent a cross-section of the community and that minority viewpoints be represented. In connection with jury size, the concern is that if the jury is too small, it will not reflect minority views. Where unanimity is departed from, the concern is that minority viewpoints represented on the jury will simply be disregarded and outvoted. A majority of the Court in Apodaca rejected this latter claim on the grounds that there was no reason to believe that majority jurors will fail to weigh the evidence and consider rational arguments offered by the minority. The dissenters argued that jury reliability was diminished in a nonunanimous system because there is less pressure to debate and deliberate. Professor Hans Zeisel has made a similar point: "[T]he abandonment of the unanimity rule is but another way of reducing the size of the jury. But it is reduction with a vengeance, for a majority verdict requirement is far more effective in nullifying the potency of minority viewpoints than is the outright reduction of a jury to a size equivalent to the majority that is allowed to agree on a verdict. Minority viewpoints fare better on a jury of ten that must be unanimous than on a jury of twelve where ten members must agree on a verdict" (1971, p. 722).
The less than unanimous verdict also poses a question not raised in the jury size cases. A majority of the Court in Johnson held that nonunanimous verdicts are not inconsistent with proof beyond a reasonable doubt and therefore do not violate due process. The fact that some members of the jury are not convinced of guilt does not itself establish reasonable doubt, a concept that apparently applies only to the standard of proof that each individual juror subjectively must apply, not a concept applicable to the jury as a group.
Are criminal defendants as well protected from conviction under a nonunanimous verdict system as under a unanimity requirement? The majority in Apodaca and Johnson conceded that juries would be hung somewhat less frequently under a nonunanimous system but also relied on social science research for the proposition that "the probability that an acquittal minority will hang the jury is about as great as that a guilty minority will hang it." Data in the same study, however, persuaded some of the dissenters that the prosecution would gain "a substantially more favorable conviction ratio" under a nonunanimous system.
By the time Burch was decided in 1979, the Court, following the pattern suggested in the 1978 jury size case of Ballew, appears to have abandoned any attempt to rely on social science to support its conclusions regarding required jury attributes. In holding 5–1 verdicts unconstitutional, the Court concluded that "having already departed from the strict historical requirements of jury trial, it is inevitable that lines must be drawn somewhere" and relied upon "much the same reasons that led [us] in Ballew to decide that use of a five-member jury threatened the fairness of the proceeding.…"
The constitutionality of other numerical combinations—for example, 8–4 or 7–5 verdicts or the various possible majorities on juries of seven to eleven members—remains in doubt. In Burch, the Court expressly reserved opinion on the constitutionality of nonunanimous verdicts by juries of more than six. Only Justice harry a. blackmun, concurring in Apodaca, commented that a 7–5 verdict standard would afford him "great difficulty."
The Court's decisions in the nonunanimous verdict cases have been designed to leave room for the states to experiment with different majority verdict systems. But the uncertainty produced by these decisions may discourage experimentation. If the states do introduce additional variations, the notions that "lines must be drawn somewhere" and that at some point "the fairness of the proceeding" is threatened hardly provide an adequate basis for selecting among the numerous lines that may be presented. If the Court is unwilling to rely upon social science research to back up its functional approach, it may find itself without a calculus for resolving constitutional issues in which specific numbers count.
Zeisel, Hans 1971 And Then There Were None: The Diminution of the Federal Jury. University of Chicago Law Review 38:710–724.