Many persuasive speeches focus on issues that require considerable thought. Should the United States adopt a national health care plan? Are certain television programs too violent for children? When an audience needs to make an important decision or reach a conclusion regarding a complicated issue, appeals to reason and logic are necessary. Aristotle used the term logos to refer to persuasive appeals directed at the audience’s reasoning on a topic.

Reasoning is the line of thought we use to make judgments based on facts and inferences from the world around us. This basic human capability lies at the heart of logical proof: when we offer our evidence to our audience in hopes that our listeners will reach the same logical conclusions as we have, we are appealing to their reason. There are two types of reasoning: inductive and deductive.

Inductive reasoning occurs when you draw general conclusions based on specific evidence. When you reason inductively, you essentially start by gathering the specific examples, incidents, cases, or statistics and draw them into a conclusion that ties them all together. For example, if you work at an animal shelter and have been bitten or snapped at several times by small dogs but never by a large dog, then you might conclude inductively that small dogs are more vicious than large dogs.

Deductive reasoning, by contrast, proceeds from the general principle to the specific examples. You begin with a general argument or hypothesis and then see how it applies it to specific cases, incidents, and locations. The most popular way to argue deductively is with a syllogism, a three-line deductive argument that draws a specific conclusion from two general premises (a major and a minor premise). Consider this syllogism:

Major premise: All cats are mammals.

Minor premise: Fluffy is a cat.

Conclusion: Therefore, Fluffy is mammal.

The speaker starts with a proposed conclusion or argument and then tests that argument by gathering facts and observations and evidence. Applied to a speech, you might use a syllogism in the following ways:

Major premise: Regular cleanings and visits to the dentist will help keep your teeth in excellent condition and reduce your chances of developing costly medical complications.

Minor premise: The proposed student dental insurance plan is affordable and provides for two free cleanings per year and additional coverage on orthodontics and dental procedures.

Conclusion: Therefore, adopting the proposed student dental insurance plan will keep your teeth in excellent condition and help you avoid costly medical complications.

The extent to which your syllogism is persuasive depends on how well the audience accepts the major premise of your case. If the people in your audience do accept your major premise that regular cleanings and visits to the dentist will help keep their teeth in excellent condition and prevent medical complications, then they may believe that the student dental insurance plan that you’re advocating is worthwhile and may be inclined to sign up. Hence, your conclusion may be acceptable to them.