You've probably heard that prosecutors have to prove criminal charges "beyond a reasonable doubt." But do you know about the other legal standards of proof?
By Ruth Maurice, Attorney UC Davis School of Law
Updated by Stacy Barrett, Attorney UC Law San Francisco
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A legal standard of proof is the amount of evidence or certainty required to prove a fact or claim in a criminal or civil case. Not to be confused with the burden of proof, which reflects which side must prove its case, standards of proof determine how much proof is necessary. Standards of proof vary based on the type of case and the stage of the proceedings. The more serious the consequences, the higher the standard of proof is likely to be. For example, a criminal case involving a potential loss of liberty (jail or prison) requires a much higher standard of proof than a civil lawsuit over money. Here are some of the most common standards, arranged from lowest to highest.
Reasonable suspicion is the amount of proof police officers need to detain someone to investigate a potential crime. For example, officers need reasonable suspicion to pull over a vehicle, briefly detain someone to ask questions, or frisk someone for a weapon. Reasonable suspicion requires an objectively reasonable belief that a suspect is involved in criminal activity, meaning the suspicion must be based on facts and not personal beliefs or feelings.
Probable Cause
Probable cause is another standard used in criminal law. Officers need probable cause to make an arrest or get an arrest warrant from a judge. Probable cause is enough information to convince a reasonable person that a crime has been committed and the suspect is probably the person who committed it. Probable cause is more than reasonable suspicion but less than beyond a reasonable doubt (more on that below).
The probable cause standard also applies at probable cause hearings when a judge must confirm that an arrest was supported by probable cause and at preliminary hearings when a judge decides whether there is enough evidence for a case to proceed to trial.
Substantial Evidence
When someone disagrees with a government agency's action, that person can ask for an administrative hearing. At the hearing, an administrative law judge (ALJ) uses a preponderance of the evidence standard (more on that standard below). For example, an ALJ uses the preponderance of the evidence standard when deciding a Social Security claim. Appellate judges who review ALJs' decisions typically use the substantial evidence standard. Substantial evidence means such relevant evidence as a reasonable mind might accept as adequate to support a conclusion. (20 C.F.R. § 404.901(2024).)
Appellate courts may also use this standard to review some findings made by trial judges and juries. When applying this standard, the appellate court's role is not to substitute its own judgment for the fact-finders but to determine whether a reasonable fact-finder could have come to the same conclusion based on the facts in the record. The idea is that the decision will stand unless no substantial evidence supports it because the judge or jury was in the best position to decide which witnesses to believe and what happened.
Preponderance of the Evidence
Civil cases are typically decided by what's called a "preponderance of the evidence" standard. For example, when someone sues another person over a car accident, a judge or jury has to decide if the person suing (the plaintiff) has proved that the other driver (the defendant) was more likely than not responsible for the accident.
Clear and Convincing Evidence
When more than money is at stake in a civil case, a higher standard of proof is typically required—clear and convincing evidence. Examples include:
The United States Supreme Court has defined clear and convincing evidence as requiring a judge or jury to have an abiding conviction that the truth of the factual contention is "highly probable." (Colorado v. New Mexico, 467 U.S. 310 (1984). Clear and convincing evidence is more than probable cause but less than proof beyond a reasonable doubt.
Beyond a Reasonable Doubt
Proof beyond a reasonable doubt is the highest legal standard. This is the standard the U.S. Constitution requires the government to meet to prove a defendant guilty of a crime. (In re Winship, 397 U.S. 358, 364 (1970).)
Courts over the years have debated the precise definition of this high standard. But there's no doubt that proof beyond a reasonable doubt is more than just a belief that a defendant is guilty. Rather, a judge or jury applying the standard must have an abiding conviction that the charge is true. Courts sometimes describe this level of confidence in a verdict as a moral certainty. If a judge or juror has a doubt based on reason about any fact necessary to convict a defendant, they must find the defendant not guilty.
