The basic objective of expository prose is to define or explain an idea, usually by expressing a thesis backed by subject sentences. A excellent example is that which is used to illustrate a scientific theory or, more simply, the reason of a conflict or war. This passage explains how electricity and magnetism are related. It is an example of expository prose because it describes both electricity and magnetism as two aspects of one phenomenon - the electromagnetic field. It does so by using language common to science textbooks: with definitions, explanations based on evidence, and illustrations (such as diagrams) of the concepts being explained. The use of simple language and clear writing style helps readers understand the concept being explained. Explanatory essays also involve presenting facts about a topic either directly or in support of a claim or argument. In academic essays this task is typically divided into several sub-parts: introduction, body, and conclusion. The introduction gives a brief overview of the essay's topic and claims while the body of the essay presents information relevant to these things. The conclusion restates the main idea of the essay and suggests possible further reading.