376 17.2 Using PersUasive strategies
Using Logic and Evidence to
Persuade
17.2 use principles of effective logic and evidence to develop a persuasive
message.
“We need to cut taxes to improve the economy,” claimed the politician on a
Sunday-morning talk show. “The stock market has lost 300 points this month.
People aren’t buying things. A tax cut will put money in their pockets and give
the economy a boost.” In an effort to persuade reluctant members of her politi-
cal party to support a tax cut, this politician was using a logical argument sup-
ported with evidence that stock prices were dropping. As we noted in Chapter 5
when we discussed how to be a critical listener, logic is a formal system of rules
for making inferences. Because wise audience members will be listening, per-
suasive speakers need to give careful attention to the way they use logic to reach
a conclusion.
Logic is central to all persuasive speeches. Aristotle said that any persuasive
speech has two parts: First, you state your case. Second, you prove your case. In
essence, he was saying that you must present evidence and then use appropriate
reasoning and logic to lead your listeners to the conclusion you advocate. Proof
consists of evidence you offer, plus the conclusion you draw from it. Evidence
is made up of the facts, examples, statistics, and expert opinions that you use
to support the points you wish to make. Reasoning is the process you follow to
draw a conclusion from evidence. The Sunday-morning talk show politician
reached a conclusion that a tax cut was necessary from the evidence that stock
prices had tumbled and people weren’t buying things. Let’s consider the two
key elements of proof in greater detail. Specifically, we will look more closely at
types of reasoning and ways of testing the quality of evidence.Understanding Types of Reasoning
Developing well-reasoned arguments for persuasive messages has been im-
portant since antiquity. If your arguments are structured in a rational way, you
have a greater chance of persuading your listeners. There are three major ways
to structure an argument to reach a logical conclusion: inductively (including
reasoning by analogy and reasoning by sign), deductively, and causally. Let’s
examine each in detail.InDuCtIve reasonIng Reasoning that arrives at a general conclusion
from specific instances or examples is known as inductive reasoning. Using this
classical approach, you reach a general conclusion based on specific examples,
facts, statistics, and opinions. You might not know for certain that the specific in-
stances prove that the conclusion is true, but you decide that in all probability, the
specific instances support the general conclusion. According to contemporary17.2