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In the 4th century BCE, Greek philosopher Aristotle authored “Rhetoric,” a tome in which he articulated three methods to present evidence in order to persuade audiences: pathos, logos and ethos. One of the three types of appeals used in an argument is “logos" or a logical appeal based on reasoning. Examples of logical appeal in persuasive writing reveal an array of techniques to introduce evidence.

Definitions of Logical Appeal

A logical appeal can pivot on a definition or claim regarding the property or nature of something. For example, nuclear activists may point to the lethal nature of radioactive fallout as an appeal for disarmament. They then must describe the actual properties of nuclear weapons to convince audiences of the harm caused to human life, animal life and the environment. The activist must also explain terms, such as radioisotopes, the cloud seeding effect and blast injuries which are used in making nuclear weapons claims.

Comparison and Analogy

The use of comparison or analogy based on evidence can either prove or refute an argument. Using an example of a persuasive essay about anti-vivisectionists, the author might note that while anti-vivisectionists condemn the killing of animals, the majority of them are actually meat-eaters. A comparison would then be made to the meat packing industry that conducts mass animal slaughter on a regular basis which exposes hypocrisy. As a rebuttal, the vivisectionists could compare the pain and anxiety suffered by animals awaiting slaughter to that of humans in line for execution. Lawyers also typically use parallel cases to buttress an argument in court.

Cause and Consequences

When people make logical appeals to advocate new policies up for debate, they typically point to the consequences of actions either taken or avoided. In the 1996 State of the Union Speech, President Bill Clinton tried to convince Congress to pass a requirement for the V-chip in TV sets. The device would enable parents to screen for unsuitable content for children. He perceived parental action as a personal responsibility, not as censorship. His statements purported that the consequences of taking no action would be the children’s exposure to possible exploitative and harmful content.

Logical Appeal of Expert Testimony

A logical appeal can leverage the testimony or opinions of experts on the argument’s subject matter. Including reputable expert testimony related to the persuasive essay idea builds credibility and an appeal to the audience's ability to reason and draw conclusions. If the paper's author backs up their persuasive argument with expert testimony, it can take the more personal persuasive idea to a new more authoritative level.

Research and Statistics

The use of research and statistics can be a powerful tool in a logical appeal. You build credibility by not only citing numbers but also leveraging the authority of the institution or scientists responsible for the numbers. Continuing in the anti-vivisectionist example, a logical example might cite a specific number of animals slaughtered or how many protests are conducted by the anti-vivisectionists. It isn't enough to just include emotional responses or the author's personal opinion. By including the statistical, logical data to back up the more emotional side of the paper, the author uses research and statistics to strengthen their paper's logical appeal and persuasiveness.