A rhetorical device is a tool that can be used in language so that the deliverer can effectively communicate a topic to the audience by helping them understand it from a different perspective. The goal of the deliverer is often to invoke emotion in the audience; however, it is not always the primary goal.
There are three categories of rhetorical devices: pathos, logos and ethos. Pathos requires that the deliverer appeal to the audience's emotions in order to communicate the message. Logos uses logic and informational ideas to communicate the message to the audience. Ethos draws upon ethics and attempts to credit the speaker by appealing to their ethical character.
Two very common examples of rhetorical devices are irony and metaphor. Irony attempts to communicate an indiscretion in the topic through the use of humor. This type of humor is subtle and is used primarily to ridicule the topic or an action within the topic. Irony has a few categories: situational irony (the irony of events), cosmic irony (attributed to misfortune), dramatic irony (a miscommunication of characters within the portrayal of a story) and sarcasm (derogatory comments toward something or someone)
An example of situational irony: an English teacher who stresses the importance of grammar fails a grammar test.
An example of cosmic irony: the world's strongest metal is used in the construction of a building, but collapses.
An example of dramatic irony: as a viewer of a horror film, you know there is a killer waiting in the room that the main character is about to walk into; however, you cannot warn them because you are not in the film.
An example of sarcasm: "they are not the sharpest tool in the tool shed".
A metaphor is used to communicate a new concept or idea to the audience by relating it to an existing idea that may help the audience better understand its context. The new concept or idea is linked to a concept that is typically well known. An example is the saying "it's raining cats and dogs". It would not literally be raining cats and dogs, but it is used to describe the intense and heavy rainfall.
There are also sonic rhetorical devices, which depend primarily on the use of sound in order to communicate the different perspective. These sonic devices include alliteration, assonance and onomatopoeia.
Alliteration is the repetition of similar sounds: "I can smell the sweet sugar all the way from the shack".
Assonance is the repetition of a set of vowel sounds: "Hear the mellow wedding bells" (the repetition of the 'e').
Onomatopoeia are words used that attempt to copy a sound: "bam!", "pow!", "crack!"