To assemble the argument effectively.
The canon of arrangement is, perhaps, the stickiest of the five. Depending upon the type of writing teacher you had in high school or college, you may have learned the 5-paragraph essay model, in which you construct a beginning, a middle consisting of proofs or explanations, and a conclusion that ties it all together.
Such a model is limited and limiting because it does not take into account that most rhetorical situations don't offer us the opportunity to construct such a neat package--assuming that's what's called for in the first place.
The 5-paragraph model also does not account differences in genre. News articles have an arrangement unique to journalism, referred to as the inverted pyramid. But even within this profession you'll discover numerous models of arrangement that do not fit the news model, e.g. editorials, investigative articles, and essays.
Finally, the 5-paragraph model will not meet the needs of all discourse communities.
The 5-paragraph model many of us learned is based on classic Greek and Roman structures. Its parts include:
You'll notice that this arrangement is very similar to the modern 5-paragraph essay except that its built for specific civic use. The concepts of the introduction and conclusion are the same. But the ancient model is more sophisticated in the middle.
The statement of fact is a narration of the issue at hand, which the 5-paragraph model would have you complete as part of the introduction. In the classic model, the introduction must also set the tone for the audience and make them favorably disposed toward the speaker. The Greeks especially were concerned that any who would speak in public establish his ethos and community connection as part of introducing an issue.
The confirmation or proof section contrasts with the refutation. The former constructs the argument; the latter challenges the argument of the opposition.
The classic model, like the 5-paragraph model, also suffers from limitations. It is not always appropriate for the rhetorical situation, the genre, or the discourse community. But, I would argue it is a more sophisticated model that can be adapted for broad use by learning and applying its principles, which I contend are these:
I would contend that all speech-acts take place within a genre. The number of genres with which the average ancient Greek citizen had to deal were limited compared to citizens in industrialized, free states today. The classic model of arrangement served them well. I would argue its principles still serve us well as long as we are aware that these are not rules.