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The phrase “One bad apple spoils the whole bunch” alludes to the spread of mold or decay from one infected apple to the rest. A person can be called a rotten apple for being a bad individual among a good group. The term has been applied especially to police corruption in the United States.

History

The phrase is an iteration of a proverb about a rotten apple spoiling its barrel, which comes from a 14th-century Latin proverb translated as "The rotten apple injures its neighbors," according to www.famous-proverbs.com.

Famous Ties

It is used by the poet Geoffrey Chaucer in “The Cook’s Tale.” It reads, “Better take rotten apple from the hoard / Than let it lie to spoil the good ones there.” The phrase as recorded in Poor Richard’s Almanac is “The rotten apple spoils his companion."

Dual Meanings

The term “rotten apple” has more than one interpretation. The traditional version is that one bad member can corrupt a group. Another meaning is when a person is accused of something wrong, they are excused by other members of the same group as a "bad apple." The implication is that the "bad apple" has not affected the entire group.

Guilt by Association

Sometimes an entire group, for example a police department, is considered corrupted by the presence of one bad officer, or “bad apple.” The corrupting influence may be isolated or the bad influence may actually persuade others to corruption.

Knapp Commission

According to the Knapp Commission, which investigated police corruption in the 1970s, rotten apples are “either weak individuals who have slipped through the screening process or succumbed to the temptations inherent in police work or deviant individuals who continue their deviance in an environment that gives them ample opportunity.” Some police departments were accused of using the rotten apple theory to minimize backlash against corruption.