One of the most essential elements of a persuasive speech or essay is the use of evidence. Evidence refers to any kind of information that supports claims that the speaker or reader makes. If claims are not supported with evidence, the listeners or readers think to themselves, "Prove it." Strong use of evidence is an essential part of a persuasive strategy. This article demonstrates the difference between a substantiated claim and an unsubstantiated claim. It then discusses the four types of persuasive evidence. Unsubstantiated Claims Versus Substantiated Claims Here are a few examples of unsubstantiated claims that are not supported with evidence. Regardless of whether these claims are factual, they offer no evidence to demonstrate that this is the case. The death penalty is a deterrent to murder. Marijuana should be illegal because it is a gateway drug that leads to the use of more dangerous drugs. A national health care system will lead to inferior health care. Lowering the drinking age is a good idea because in countries with lower drinking ages, it's less taboo and there's less alcohol abuse. Claims like these are sometimes mistakenly made with the assumption that the audience will agree, and therefore no further evidence is needed. However, this is not true. Here are a few possible ways to substantiate these claims with evidence. Death penalty as deterrent: Statistics that show a correlation between the use of the death penalty and a reduction in murders. Marijuana as gateway drug: A medical study that demonstrates the gateway effect. Inferior health care: A discussion of another country that implemented national health care and suffered from a decrease in quality. Drinking age: A comparison of alcohol abuse in countries with high drinking ages versus low drinking ages. Types of Evidence There are four kinds of evidence that can be used in a persuasive speech or essay: (1) statistical or factual evidence, (2) anecdotal evidence or examples, (3) expert evidence, and (4) analogical evidence. Statistical or factual evidence. This kind of evidence involves using large, measurable amounts of information to back up a claim, such as statistics or other numbers. The purpose of this kind of evidence is to demonstrate that something is true all or much of the time. Usually, statistics and factual evidence should make up the largest chunk of information in a persuasive speech or essay. Some examples of this kind of evidence to include in the topics discussed above include: Murder rates in ten of the U.S. states that have a death penalty Several large studies that show the percentage of LSD and heroin addicts who took marijuana first Death rates in relation to several diseases in countries both before and after a national health care system was implemented Percentage of the population who are alcoholics in countries with lower drinking ages and countries with higher drinking ages Anecdotal evidence or examples. This kind of evidence involves telling stories of individuals afflicted by a problem related to the topic, or individual examples of incidents that support a claim. This kind of evidence must be used to supplement statistical or factual evidence and should not dominate the speech or essay, since, after all, it's always possible to find one example of just about anything. However, this kind of evidence should not be omitted entirely because it has an emotional quality that can go a long way when trying to persuade. Some examples: Story of a woman murdered by a paroled killer in a state that doesn't have the death penalty. Story of a teenage girl who died of a heroin overdose and who started using marijuana at age 12. Story of someone who died of a treatable disease after waiting several months for a routine procedure in a country with nationalized health care. Story of a college student in a country with a low drinking age who does not abuse alcohol. Expert evidence. This kind of evidence is provided by people who have the credibility to know what they're talking about, usually because of educational or professional expertise. It's important to choose expert evidence that isn't biased. Here are a few examples: A study from a criminal justice department of a major university that argues that the death penalty can be a deterrent to murder. A quote from a prominent doctor who works with drug addicts about the role of marijuana as a gateway drug. A United Nations task force study that examines the pros and cons of national health care. An alcohol abuse center director in a country with a high drinking age who previously worked in a country with a low drinking age. Analogy evidence. This kind of evidence involves comparing two things that are very alike, and showing that because something is true for A, it's true for B as well. In order to make this work, it needs to be established clearly that A and B are alike enough for this the analogy to work. Some examples: Comparing murder rates in a state with no death penalty to murder rates in a state with the death penalty. Discussing the problems in a country that has national health care as an analogy for problems that will happen if health care is nationalized in another country The Importance of Evidence in a Persuasive Speech or Essay Unsubstantiated evidence is one of the biggest problems with persuasive speeches and essays. Without evidence, persuasion is hard to pull off. Solid use of the different kinds of evidence is important in creating speeches and essays that really work.
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