E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Cui bono?
Who is benefited thereby? To whom is it a gain? The more usual meaning attached to the words is, What good will it do? For what good purpose? It was the question of Judge Cassius. (See Cicero: Pro Milone, 12, sec. 32.)
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“Cato, that great and grave philosopher, did commonly demand, when any new project was propounded unto him, cui bono, what good will ensue in case the same is effected?”—Fuller: Worthies (The Design, i.).
