The 12 member jury is generally considered a “historical accident.” When the US was formed, deference was given to many examples of English common law (law derived from custom rather than statute), and the twelve member jury was one of them. In other words, we’re doing it because the guys before us were doing it, who were doing it because the guys before them were doing it.
The founding fathers didn’t seem to consider the number 12 worthy of specification. Article III of the Constitution holds the “Trial of all Crimes, except in Cases of Impeachment, shall be by Jury.” And the 6th Amendment adds “In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the state and district wherein the crime shall have been committed.”
The framers of the Constitution definitely thought juries should exist and that they should be impartial. However while the composition of these impartial trial juries wasn’t spelled out statutorily, in practice they followed the common law AKA 12 white dudes in a box.
This became official in 1898 when Thompson v. Utah prompted the Supreme Court to hold “the jury referred to in the original Constitution and Sixth Amendment is a jury constituted, as it was at common law, of twelve persons, neither more nor less.” So, there it was in black and white. The Supreme Court saying juries must have 12 members.
... For a while. In 1967 Florida changed its law and permitted criminal trial juries be comprised of only 6 members. (The new law also allowed women to serve on juries for the first time, so… wow.)
A man named Williams challenged that in 1970, but in Williams v. Florida the court held that the constitution did not require any specific number of jurors and that there was “absolutely no indication” that a jury have the same characteristics of juries under English common law.
And so, depending on what state you’re in, the makeup and outcome of your trial jury could be radically different. 1972 cases Apodaca v. Oregon and Johnson v. Louisiana found that 10-2 and 9-3 votes were permissible under the Constitution, so even unanimity isn’t always a requirement to make it to prison. A few things, however, you can depend on.
No matter where you are, you’re guaranteed at least six jurors (thanks to Ballew v. Georgia) and if you have as few as six jurors - they’ve got to be unanimous (Burch v. Louisiana). If the state - any state - wants to send you to death row, rest assured you’ll need 12 unanimous jurors to get there.
However, the question lingers for many regarding six member juries - is it enough?
Outrage followed the 2013 acquittal of George Zimmerman, who himself had a six member jury. One argument against six member juries is that they don’t allow for as inclusive a cross-section of the community as twelve member juries, and Zimmerman’s all female, ethnically homogeneous jury seemed to bolster that claim. (All were white except one Latina.)
Proponents of the six member jury structure argue that the diversity and reliability of smaller juries isn’t compromised, and that they hang less often and save money and time.
I can’t say Florida is doing it right by permitting six member juries to decide criminal trials, but I’ll give Florida this. At least it hasn’t kowtowed to tradition for the sake of tradition. Perhaps larger juries are necessary to ensure fair outcomes, but what’s foolish is the presumption they do.
Albert Einstein said “The important thing is not to stop questioning.” We should be having a discussion collectively about what jury size is appropriate, and whatever outcome is reached needs to be determined on reason, logic, and scientific evidence. Not English common law or tradition or a negligence to ask the question, why? No one deserves to find him or herself on the wrong side of a verdict because of a “historical accident.”