What is "cui bono"

Cui bono \Cui` bo"no\ [L.] Lit., for whose benefit; incorrectly understood, it came to be used in the sense, of what good or use; and hence, (what) purpose; object; specif., the ultimate object of life.

a Latin phrase from Cicero. It means "to whom for a benefit," or "who profits by it?" not "to what good purpose?" as is often erroneously claimed. From cui "to? for whom?," an old form preserved here in the dative form of the interrogative pronoun quis "who?" (see who) + bono "good" (see bene-).

n. The principle that the ultimate initiator of an action is likely he who stands to gain from the action.

Cui bono , literally "to whose profit?", is a Latin phrase which is still in use as a key forensic question in legal and police investigation: finding out who has a motive for a crime. It is an adage that is used either to suggest a hidden motive or to indicate that the party responsible for something may not be who it appears at first to be.

The phrase is a double dative construction. It is also rendered as cui prodest ("whose profits ').

Commonly the phrase is used to suggest that the person or people guilty of committing a crime may be found among those who have something to gain, chiefly with an eye toward financial gain. The party that benefits may not always be obvious or may have successfully diverted attention to a scapegoat, for example.

The Roman orator and statesman Marcus Tullius Cicero, in his speech Pro Roscio Amerino, section 84, attributed the expression cui bono to the Roman consul and censor Lucius Cassius Longinus Ravilla:

Another example of Cicero using "cui bono" is in his defence of Milo, in the Pro Milone. He even makes a reference to Cassius: "let that maxim of Cassius apply".