The Art of Persuasion: Logic in Rhetoric

Rhetoric is about persuasion. It is focused on gaining the assent of the audience. To this end, it makes use of three types of appeal in combination: logos (logic), pathos (emotion) and ethos (character).

First, we look at logos, the appeal to logic. You must assume that your audience is capable of reason (except, perhaps, in unusual circumstances), and even somewhat skeptical, and therefore you must make your argument reasonable. You may be tempted to skimp on the logic if you are speaking to a largely receptive and supportive audience, but this is usually a mistake. If you craft your argument so that your logic can withstand the most critical mind, you will have strengthened the conviction of your supporters and even provided them with the tools to persuade others. Your argument must flow in a logical fashion from premise to conclusion, built one block upon another. It begins with a premise that your audience already accepts as true, and continues, step by step, to a logical conclusion. The appeal of your logic will form the scaffolding of your argument, upon which you will add ethos and pathos. In developing a logical argument, you must take into consideration what manner of argument will be most likely to appeal to your particular audience. For example, you would not successfully use the claim that the Bible supports capital punishment if you were appealing to a secular audience.

Let us look at a simple argument that we can break up into its constituent parts:

"Universities are full of knowledge. The freshmen bring a little in, and the seniors take none away, and knowledge accumulates." ~ Harvard President A. L. Lowell

Premise 1: Freshmen bring a little knowledge.
Premise 2: Seniors take none away.
Premise 3: Knowledge accumulates.
Conclusion: Universities are full of knowledge.

*From http://owl.english.purdue.edu/handouts/general/gl_logic.html

Building your argument by outlining your logic (premises and conclusions) is a very powerful way to set it up. You might find dazzling flaws in your argument by outlining it in this way, but you will be able to make your argument stronger and more likely to succeed by building it on a logical outline.

(Check back tomorrow as this series continues.)

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