In rhetoric, a rhetorical device or resource of language is a technique that an author or speaker uses to convey to the listener or reader a meaning with the goal of persuading him or her towards considering a topic from a different perspective. While rhetorical devices may be used to evoke an emotional response in the audience, there are other reasons to use them. The goal of rhetoric is to persuade towards a particular frame of view or a particular course of action, so appropriate rhetorical devices are used to construct sentences designed both to make the audience receptive through emotional changes and to provide a rational argument for the frame of view or course of action.
Two rhetorical devices are irony and metaphor.
The use of irony in rhetoric is primarily to convey to the audience an incongruity that is often used as a tool of humor in order to deprecate or ridicule an idea or course of action.
The use of metaphor in rhetoric is primarily to convey to the audience a new idea or meaning by linking it to an existing idea or meaning with which the audience is already familiar. By making the new appear to be linked to or a type of the old and familiar, the person using the metaphor hopes to help the audience understand the new.
An example of rhetorical device is this passage attributed to a speech by Abraham Lincoln about a political adversary in which Lincoln said that his adversary had "dived down deeper into the sea of knowledge and come up drier than any other man he knew".
This attributed quote uses a body of water as a metaphor for a body of knowledge with the ironical idea of someone who gained so little from his education that he achieved the impossible of jumping into a body of water and climbing back out without getting wet.
Some Rhetorical Devices:
Sonic devices depend on sound.
1. Alliteration is the repetition of the beginning sound of a word. This device is used to emphasize something, especially some kind of threat, bad or danger. For example, "The zoo kept several selfish seals".
2. Assonance is the repetition of a similar set of sounds, it is used to emphasize intensity, evil, etc.
3. Cacophony is the eruption of chaotic, awful sound.
4. Onomatopoeia uses one or more onomatopoeic words (words that sound like what the author is describing).
Devices of Altered Signification shift the meaning of words.
1. Metaphor directly says something is something else. For example, "his beard was a lion's mane".
2. Simile is a gentler form of metaphor which tends to use "as" or "like" to compare something to something else. For example, "his beard was like a lion's mane."