The following are the most common standards of proof in civil and criminal cases, from lowest to highest. The standard that applies depends on the type of case. The more serious the consequences, the higher the standard of proof is likely to be. Potential loss of liberty (jail or prison), for example, involves a higher standard of proof than a lawsuit for money.
(For an important distinction in legal terms, see "What's the difference between the burden of proof and the standard of proof?")
STANDARDS BEFORE TRIAL
Some legal standards aren't used by jurors at a trial, but by judges who must make determinations at pretrial hearings. In criminal cases, two such standards are reasonable suspicion and probable cause. These standards are most often at issue when defendants file motions to suppress evidence. Preliminary hearings also involve a determination of probable cause.
At an administrative hearing, an administrative law judge (ALJ) reviews the decision of a government agency, such as the DMV or an unemployment agency. A citizen affected by the decision brings a challenge, and the ALJ reviews the decision. Appellate judges who in turn review administrative judges' decisions often use the "substantial evidence" standard. This standard falls between probable cause and preponderance of the evidence, and requires more than a "mere scintilla of evidence." Substantial evidence is "such relevant evidence as a reasonable mind might accept as adequate to support a conclusion." (Richardson v. Perales, 402 U.S. 389 (1971).)
The preponderance-of-the-evidence standard is the default for most civil lawsuits. In these cases a plaintiff is typically suing a defendant for lost money because of acts like breaking a contract or causing a car accident (the money loss might be due to vehicle damage and medical bills, for example). Preponderance of the evidence is met if the trier of fact (judge or jury) believes the evidence shows the defendant is more likely than not—more than 50% likely to be—responsible.
The clear-and-convincing-evidence standard goes by descriptions such as "clear, cogent, unequivocal, satisfactory, convincing" evidence. Generally, this standard is reserved for civil lawsuits where something more than money is at stake, such as civil liberties. Examples include:
(Conservatorship of Wendland, 26 Cal. 4th 519 (2001); Santosky v. Kramer, 455 U.S. 745 (1982).)
"Clear and convincing" means the evidence is highly and substantially more likely to be true than untrue; the trier of fact must have an abiding conviction that the truth of the factual contention is highly probable. (Colorado v. New Mexico, 467 U.S. 310 (1984).
"Beyond a reasonable doubt" is the highest legal standard. This is the standard the U.S. Constitution requires the government to meet in order to prove a defendant guilty of a crime. (In re Winship, 397 U.S. 358, 364 (1970).)
Courts over the years have debated the extent to which the government has to prove its case to meet this high standard. But it's clear that, according to the standard, it's not enough for the trier of fact to simply believe the defendant is guilty. Rather, the evidence must be so convincing that no reasonable person would ever question the defendant's guilt. The standard requires that the evidence offer no logical explanation or conclusion other than that the defendant committed the crime. Courts sometimes describe this level of confidence in a verdict as a moral certainty.
"Beyond a reasonable doubt" doesn't mean, however, that the prosecution must eliminate all unreasonable doubts a jury could possibly have. Nor must the prosecution prove the case beyond a shadow of a doubt or to an absolute certainty. These would be impossible burdens because only witnesses to an alleged crime can be certain—and even then, not all witnesses can be certain. Rather, this highest of standards requires—after consideration of all facts—only one logical conclusion: that the defendant is indeed guilty.