In writing as well as in speech, the rhetorical function of a definition is important since properly defining a term is evidence that the writer/speaker has a strong grasp of his subject. In scientific and academic papers, the writer often begins by defining the terms he will be using throughout his analysis. This demonstrates expertise in the field and, by defining the terms he will later use, the writer makes sure his readers are all on the same page and interpret these terms in the same way. This makes the writer's work more formal and professional, and thus more convincing to the reader.
When authors and public speakers are speaking critically, to sound trustworthy and to persuade their readers and audience, they must explain why they hold certain views and provide reasons, effects and explanations for their claims. They convince their readers and audience by offering reasons why something is a certain way, the actions that need to be taken to change the situation, ways to go about changing it and why it should be changed. By stressing causes with phrases like "because of" and "owing to the fact that" and emphasizing the results of actions with connecting words like "therefore" and "consequently," writers and speakers establish rhetorical function in their writing and speech.
When authors and speakers successfully lay out every piece of information, define their terms, provide all the evidence and explain the different reasons and consequences that have led them to a certain conclusion, that conclusion will be highly persuasive. A good epilogue is an effective way to end a speech or paper, but it needs to follow logically what has already been discussed throughout. A strongly rhetorical conclusion is the one that clearly proves that the writer/speaker has established what he set out to demonstrate at the start and has convinced his readers/audience of the truth and logic of his argument. Phrases like "to conclude," "on this basis," "given this" and "in conclusion," when starting his conclusion, help the author/speaker establish rhetorical function in his speech and writing.
In both writing and speaking, it is inevitable that the writer/speaker will try to simplify things to help the readers or audience better understand the matter examined. These simplifications and generalizations, however, need to be supported by examples. The rhetorical function of examples is noteworthy, as they make the writing or speaking more comprehensible and persuasive.