Expository text has a single mandate: it relays information to which the writer is privy in a manner that will be clearly understood by the reader. The writer’s mission is to teach, inform, reveal and/or amplify ideas and knowledge. This mode of writing requires that the writer analyze his or her topic. He must group ideas, select the best examples, and/or structure his explanation in a manner that is clear and convincing to his audience.

There are many different purposes for writing expository text. Some of them are to:

Because the mission in constructing expository text is to convey meaning clearly, the writer must present his ideas in a deliberate and organized manner. Regardless of the organizational structure he chooses, the writer must explain the relationships and connections between ideas through examples, facts, and anecdotes.

The key to writing effective expository text is for the writer to have a clear understanding of

1. the purpose (mode)
2. the best form (product) to use to get this idea across
3. how to best present the ideas (organizational structures).

The diagram below illustrates the dynamic relationship between expository modes, forms, and organizational structures:

Depending on his purpose, a writer may face certain restrictions when producing a product. In the case of the diagram above, let's assume this writer is faced with the challenge of producing a brochure. (Another scenario might be that he was faced with writing an explanation of something and chose the brochure as the form by which to deliver this information.) Now, a brochure is an advertising tool and its purpose or goal is to promote a business or organization. Whether that business is a bed and breakfast or a sportsmen's fishing lodge, the writer's goal will be the same: he will need to provide an explanation of the services and amenities that set him apart from others in that business. Organizations use brochures a little differently. They identify their target issues and may provide an overview of the activities to which the public is invited to participate.

Depending on the message the writer means to convey, he might use one or more organizational structure to drive home his point(s). Neither of the businesses listed above would seem well served by employing a cause and effect or problem/solution organizational structure; however, were the brochure produced to promote a salmon stream restoration or conservation business or organization, both strategies would seem quite appropriate. Using sequential or circumlocution organizational strategies might better serve the other two businesses, the B&B and the lodge.

Under the umbrella of expository text are a plethora of modes. Some examples of these are argumentation, explanation, process analysis, critical review, informational writing. Each has implicit expectations:

Argumentation: The writer takes a stance on an issue. His view is clearly stated, usually as a thesis statement. Anecdotes, facts and examples are presented in order to explain the writer’s opinion and convince the reader that the idea is at least credible.

Critical review or response: A writer first analyzes that which s/he is reviewing based on predetermined criteria then presents his critique. For example, a movie could be discussed in terms of its social value (Boys Don’t Cry; Norma Rae, Erin Brockovich), a book in terms of its literary quality.

Explanation: The writer describes his/her impression, observation, belief or observation about something.

Persuasion: This mode is similar to argumentation, but it "ups the ante." The writer must move beyond merely presenting a viable argument. He must convince the reader to hold a prescribed opinion or to take a certain action.

Process or procedural analysis: The writer tells a reader how to do something or describes how something is done.

Expository text can be written in one of a number of forms. The term, "form," simply refers to the product being produced. If one were to write an explanation, (mode) for example, he might produce a brochure or an essay (form). Although both products have the same objective, to provide an explanation, the organizational and content expectations of each differ significantly. Forms that lend themselves to the construction of expository text include: