Types of Evidence

As in claims, you can choose among different types of evidence to support these claims, including the supporting materials described in Chapter 8 (“secondary sources”) and your own knowledge and experience (“speaker expertise”).

Secondary Sources (“External Evidence”)

The most common form of evidence is secondary sources—the examples, narratives, testimony, facts, and statistics described in Chapter 8. Sometimes called external evidence because the knowledge comes from outside the speaker’s own experience, secondary sources are most powerful when they impart new information that the audience has not previously used in forming an opinion.6 Thus, for a persuasive speech it can be particularly effective to offer supporting material that your audience is not likely to know but will find both persuasive and credible.

But even strong external evidence may not be enough to convince your audience of certain claims. This is especially the case with claims of value and of policy. For example, no matter how many facts or how much expert testimony you cite to prove that Congress should raise the minimum wage, unless you can show the audience doing so can benefit them in some way, they aren’t likely to care enough to actually do anything about it. Thus, as described in Chapter 24, offering evidence that is related to the audience’s needs and values is a crucial aspect of supporting many persuasive claims. If asking your classmates to join in advocating for a higher minimum wage, for example, you could appeal to their needs by offering evidence that relates directly to them: “In our class, 73 percent work at least 15 hours a week, and 82 percent of us earn the minimum wage . . . ”

TABLE 25.1 Sample Claims for Arguments of Fact, Value, and Policy

Type of Argument Claim of Fact Claim of Value Claim of Policy
(Focuses on whether something is or is not true or whether something will or will not happen) (Addresses issues of judgment) (Recommends that a specific course of action be taken, or approved of, by an audience)
Sample Claim
  • Demand for online college courses will outpace bricks-and-mortar classes in the next decade.
  • Mandatory minimum sentencing is unfair.
  • Assisted suicide is immoral.
  • Until final legislation on immigration is passed, all deportations of illegal immigrants should cease.
  • Taxes on inheritance should be abolished.

Speaker Expertise as Evidence

When the audience will find your opinions credible and convincing, consider using your own speaker expertise as evidence. Few persuasive speeches can be convincingly built on speaker experience and knowledge alone. Offered in conjunction with other forms of evidence, however, your expertise can help audience members identify with you and add some credibility to your claims. Using speaker expertise as evidence for a claim on the need to purchase health insurance might work like this:

CLAIM: Young adults need the protection of a health-insurance plan.
SPEAKER EXPERTISE AS EVIDENCE: I thought that being young and healthy, I didn’t need insurance . . . until I suffered a complex fracture requiring surgery and costing many thousands of dollars . . .
WARRANT: The young and healthy are also vulnerable and need to protect themselves against unforeseen events.