Description communicates what things are like according to the five senses; the way things sound, look, taste, feel and smell are given in detail. This type of discourse is good at evoking atmosphere or mood and is helped by the use of metaphors and similes.
The purpose of argumentative discourse is to get the listener or reader to agree with what is being said through evidence and reason. Argument tries to elicit agreement through the use of logic, figures, facts, illustrative examples and expert testimony; emotional appeals may also be used. An argument may be persuasive if its purpose is not only to get the reader or listener to agree but also to get them to act on that belief.
Narration involves telling a series of events, usually in the order that they happened. Narration is essentially storytelling, and is often used in forms such as fairy tales. This type of discourse may relate events that are fictional or nonfictional.
Expository discourse is used to inform. Exposition can be used to compare and contrast, define, analyze, classify, show cause and effect or lay out a problem and its solution. This type of discourse usually has a distinct type of organization and structure that is easy to follow.