What kind of device is used when an author employs the phrase "the pen is mightier than the sword"?

The phrase "the pen is mightier than the sword" employs metonymy, which is a figure of speech in which a thing or concept is referred to by the name of something closely associated with it. In this case, the "pen" symbolizes writing, communication, or intellectual power, while the "sword" represents military force or violence. This expression suggests that the power of ideas and words can be more influential and effective than physical force.

Metonymy works effectively here because it connects two ideas (writing and warfare) through a related concept (the instruments themselves—pen and sword), illustrating their contrasting powers. While metaphor, alliteration, and simile are also literary devices, they do not apply to this phrase in the same way. A metaphor directly compares two unlike things, alliteration involves the repetition of consonant sounds, and a simile explicitly compares two different things using "like" or "as," none of which are characteristics of this specific phrase.