What Does a Jury Do?
By the BrainSnail editorial team. How these articles are written and checked, and how to tell us when one is wrong.
A jury decides questions of fact, not questions of law. That single distinction explains almost everything about how juries work, including why a jury can acquit someone who seems obviously guilty and why the judge, not the jury, decides the sentence.
What the jury does that the judge does not
The division of labour is precise. The judge decides what the law is, what evidence the jury is allowed to hear, and how to instruct them. The jury decides what happened, based only on the evidence presented in court.
So a jury never rules on whether a law is fair or how it should be interpreted. It answers a factual question: given this evidence, are we satisfied that the defendant did what is alleged, to the required standard?
How jurors are chosen
Jurors are selected at random from a broad pool, typically drawn from electoral or residence records. Randomness is the point, because a panel chosen by either side would defeat the purpose.
Selection then removes those who cannot serve fairly. People connected to the case, or with a direct interest in it, are excluded. Systems differ considerably in how much either side can challenge individual jurors, with some jurisdictions allowing extensive questioning and others very little.
How a verdict is reached
Jurors deliberate in private with no outside contact about the case. Most systems ask first for unanimity and may accept a majority verdict after sufficient time has passed.
A few features are near universal:
- •Deliberations are secret, and jurors are not required to explain their reasoning
- •The burden of proof stays with the prosecution throughout
- •If jurors cannot agree, the result is a hung jury and a possible retrial
- •Jurors must decide only on evidence heard in court, not their own research
Why juries exist
The historical argument is about placing a check between the state and the individual. A government can write laws and appoint judges but it cannot easily control twelve randomly selected citizens, and that has been seen as a safeguard against oppressive prosecution.
There is also a legitimacy argument. Verdicts reached by ordinary members of the community are often more readily accepted than decisions handed down by officials, particularly in contentious cases.
The criticisms
Juries are not universally admired. Critics point to the risk of bias, the difficulty of understanding complex financial or scientific evidence, and the fact that no reasons are given, which makes appeals harder.
Some countries use professional judges alone, or mixed panels of judges and lay members. Even in jury systems, the vast majority of criminal cases never reach a jury, being resolved by guilty pleas or heard in lower courts. The jury trial is emblematic but statistically rare.
Jury nullification
A jury can acquit even when the evidence clearly establishes that the defendant did what is alleged, and because deliberations are secret and no reasons are given, nothing can be done about it. This is usually called jury nullification.
It is not a right that juries are told they have, and in most jurisdictions lawyers are not permitted to invite it. It has been used historically both admirably, in refusing to convict under laws seen as unjust, and appallingly, in refusing to convict defendants who harmed people the jury did not value. It is best understood as an unavoidable consequence of secret deliberation rather than a designed feature.
The takeaway
A jury decides questions of fact using only the evidence presented, while the judge decides the law and the sentence, and the system exists mainly as a check on state power in the hands of ordinary citizens.