Purpose is the reason why a text was created. This may be, for example, to entertain, explain, instruct, persuade or inform. The purpose of a text is its writer or speaker’s controlling idea: the message they wish the text to leave with the reader or listener. When you consider a text’s purpose, you need to recognise how the writer has chosen stylistic devices to bring about a particular series of effects on the reader. One of the most common purposes is to persuade – and it can be one of the most difficult to determine because professional writers are experts at making persuasion appear to be information: quite a different thing (as wartime propaganda has shown). Audience is also a way to categorise texts.

» Linguistic Library (Mike Green)