So far, Heinrichs has been talking about how to get the audience to think of the speaker in a favorable light. Now, it’s time to discuss how to use logos to persuade an audience. Perhaps the most challenging aspect of arguing is not knowing enough about an issue to win. But as important as a command of the facts is, it’s not the be-all, end-all. Logos allows the skilled persuader to skip the facts and focus on rational strategy and definition. Logos is also invaluable for refuting an opponent’s argument when you lack a command of the facts: even if you don’t know everything, you’ll be able to recognize your opponent’s logical fallacies.
Although logos could be the most obvious part of an argument, Heinrichs doesn’t discuss it until after discussing ethos and pathos at great length. In doing so, he emphasizes that logic isn’t the be-all, end-all of debate. However, he also makes it clear that good rhetoricians must have at least a basic command of logic; indeed, a good rhetorician can often do more in an argument with the rules of logos than with the facts themselves—even if they don’t know all the facts, they can spot logical errors.
As it’s taught in universities, formal logic is probably too rigorous and mathematical to be of much help in day-to-day conversation, and in fact, some arguments that would be considered fallacious in a university classroom are rhetorically acceptable. Indeed, there’s an important difference between logic and logos (which simply means, “word” in Greek). Logos allows the persuader to use facts as well as values and attitudes to make a convincing case.
Logic and logos aren’t the same at all: logos is often more concerned with enlisting logic in order to make a strong point. A completely rational persuader who doesn't draw on values and attitudes will never be as successful as a rhetorician who employs logos in all its forms.
To understand rhetorical logic, Heinrichs looks at the syllogism, a logical technique that’s more or less useless in daily conversation. An example: “All men are mortal; Socrates is a man; therefore, Socrates is mortal.” Sometimes, businesses and marketers use more complicated syllogisms to determine the total available market for a product. For example, if a company determines that lots of people aged twenty-five to forty read a magazine, and if the magazine’s ads sell cars, then a car company might want to advertise in the magazine. Ads sometimes use fallacious syllogisms; for example, the implicit message of many car commercials is, “Babes go for people who drive our car; therefore, if you go for babes, you should buy our car.”
Understanding syllogisms might seem altogether irrelevant to most people’s day-to-day lives, but in fact, syllogisms lie at the heart of modern advertising. Without identifying the different groups that comprise a potential market, businesses would have no way of knowing how to sell their product. At the simplest level, syllogisms are a way of studying the relationship between different overlapping groups, and advertising itself could be considered the study of different groups (namely, buyers).
Logical formulations that use the structure of the syllogism fall into the category of deductive logic, beginning with a premise, applied to a specific case, in order to reach a conclusion. Another kind of logic is inductive logic, which begins with specific cases and then uses those cases to prove a premise or conclusion. For example, an inductive logician might observe that all humans born more than 150 years ago are dead, and conclude that all humans are mortal. The fictional character Sherlock Holmes was a master of deductive logic: he used his vast knowledge of premises to draw surprising, unexpected conclusions about specific people.
Deductive and inductive logic aren’t the only two schools of logic, but they’re the two that Heinrichs finds most relevant to the art of rhetoric. Interestingly, some philosophers, such as Karl Popper, have argued that induction is technically never possible—in other words, any inductive conclusion about a given group is a logical fallacy. For the purposes of rhetoric, however, Heinrich treats deduction and induction as valid intellectual maneuvers.
In a deliberative argument, the conclusion is a choice about how to behave. Many deliberative arguments use inductive logic. For example, a toothpaste ad that says, “nine out of ten doctors recommend” it is encouraging the viewer to make an induction about the product’s quality. Deliberate arguments might also use deductive logic, offering a premise in support of a specific conclusion.
Commercials tend to use forms of inductive logic or deductive logic to sway their viewers; however, many of these methods of persuasion commit logical fallacies, as Heinrichs will discuss in the following chapter.
Sometimes, it can be difficult to tell the difference between an argument’s conclusion and its proof. A persuader’s conclusion doesn’t always follow from their proof and premises. Once, Heinrichs had an exchange with someone who followed his blog about teaching intelligent design in schools. Heinrichs claimed that schools shouldn’t be required to teach both creationism and biology in science classes, while the follower argued that teachers should teach both theories as scientific hypotheses. Heinrichs responded by pointing out that intelligent design advocates refuse to name the designer of the universe. Therefore, there are two possibilities: 1) intelligent design advocates believe that some events have no cause, or 2) intelligent design advocates believe that a supernatural being created the universe. If 1), then intelligent design isn’t logical, and if 2), it’s not scientific; in either case, it shouldn’t be taught in science courses.
The proof of a logical argument either stems from studying examples (inductive logic) or studying the relationship between multiple groups (deductive logic). Here, Heinrichs employs both inductive and deductive logic in order to show that intelligent design shouldn’t be taught in high school science classrooms (deductively, he defines a category, science, and then shows how intelligent design fails to fall into that category; inductively, he lists a series of possibilities about intelligent design and shows how they point to the same conclusion—intelligent design shouldn’t be taught in schools).
Heinrichs returns to Annie, who was trying to convince Kathy to consider voting Democratic (Kathy insisted that the Democrats would raise taxes). Annie could use induction, arguing that, since she lives in a Republican state where the taxes are high, and since Congress continues borrowing money, it’s likely that Congress will continue raising taxes. Therefore, she could say, both Democrats and Republicans will raise taxes—and it makes more sense to vote for the party that’s honest than the one that lies about taxes.
Inductive logic would suggest that both the Democrats and the Republicans will raise taxes, even if the Republicans aren’t saying that they will. From here, Annie can use an appeal to Kathy’s shared moral values to suggest to Kathy that she should vote for the more honest party.
Often, the strongest arguments combine induction and deduction. A persuader can make use of the facts, but can also strengthen their point with comparisons, or even tell a story. When trying to convince a friend to play poker instead of going to a concert, you could employ all three approaches. You could remind him that he likes cigars and home cooking (facts). You could also tell him that the opera won’t allow him to drink beer, while playing poker will (comparison), or you could tell him about another friend who died at the opera (story). All three approaches could work. Heinrichs concludes by encouraging readers to scope out their significant others’ commonplaces, and try to persuade their significant others with facts, comparisons, and stories.
Induction and deduction can be powerful bases for an argument, especially if they’re bolstered with stories, facts, and comparisons. Logos may not be the be-all, end-all of arguing, but it’s an important aspect of a good argument.