Harper wants to convince his parents to help him buy a new car. He tells his parents that his current car is A) old, B) unsafe, and C) pretty ugly. His argument doesn’t work. His parents reply that A) it is already paid-off, B) they did a lot of research and specifically chose this car for its good safety ratings, and C) they don’t care that it is ugly. Rather than give up, Harper considers what he learned about his parents from this discussion: First, they don’t want him stuck taking on loan payments. Second, they care a lot about how safe his car is. Third, they care a lot less than he does about how the car looks. With this new information, he starts doing his research and coming up with a better argument.

The following week, Harper approaches his parents again. This time, he proposes a specific car that he wants: a newer, much prettier version of his old car. He knows exactly how much the car will cost, and he can pay for half of it with the money he saved from his summer job. “In fact,” he says to them “if you will pay for the other half, it would mean I won’t have to worry about having a car-payment for a long, long time.” Then, he explains how the new model of the car is similar to the old one, but with many new safety features. He points out how it gets the highest possible safety ratings. “I know how important it is to you that I drive something safe,” he says, “Buying this now would immediately make me safer, and it would mean I spent the next 10 years in one of the safest cars on the road.” He doesn’t mention how much nicer the new one looks.

His parents look at each other. His dad cracks a small smile. “We can go test drive one tomorrow. Then we will decide.”

Now it is Harper’s turn to smile. He is going to like his new car.

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Logos describes persuasive appeals based in logical reasoning. Logos relies on reason to persuade, and is created by the information you choose to present and how you choose to organize it. Aristotle (n.d.) believed there was an art to this, and that speakers could be effective by choosing the right arguments and organizing them in a way that moves their particular audience. If done well, your audience should find that the information you provide naturally leads to the conclusions you wish them to reach. But how should you do this? This chapter provides some guidance on the key parts of logical arguments, how they fit together, and the importance of matching your argument to your audience.

The Toulmin Model is a model of argumentation created by the philosopher Stephen Toulmin (2003). In this model, the essential parts of an argument are a claim, data, and a warrant. A Claim is a statement the speaker wants the listener to believe. Claims can vary from non-controversial and easily-verified: “it is raining outside,” to highly-contested and difficult to assess: “going to college is a bad investment.” Some claims are easily accepted. If your roommate walks into your apartment and says “it is starting to rain outside,” you probably accept what they are saying as true without taking the time to go outside and check for yourself. Other claims are not accepted so easily and require the speaker to support their claim with data and warrants.

Data (sometimes called grounds) are the evidence provided in support of a claim. There are many different types of data ranging from scientific studies and statistics to personal anecdotes or observations. Different types of claims require different types of data to support them. For example, the major claims in a scientific study generally require carefully collected evidence interpreted using other scientific studies. Without these, other scientists will not believe the claims. However, if a friend tells you that you should take a certain class next semester, the fact that your friend took it and liked it might be good enough evidence to convince you.

Again, the more controversial the claim, the more important it is to provide strong data to support it. If someone’s claim is that “going to college is a bad financial investment,” pointing to a few very wealthy people who did not go to college is not very convincing data. This is particularly true because there is a lot of research suggesting college graduates make substantially more money over their lifetimes. In other words, the majority of the data does not support their claim. However, if the person changed their claim to “it is POSSIBLE to get rich without going to college,” those few examples they provided would be much better data to support that particular claim.

A Warrant is how your data logically supports your claim. Warrants are often overlooked by both speakers and audiences, because we often leave them unsaid. They are frequently assumed and taken for granted. If a friend recommended a class to you, they might say something like:

You should take Public Speaking next semester. (claim)

I’m taking it this semester and it is a fun class. (data)

Imagine if, instead of this, your friend said: 

You should take Public Speaking next semester. (claim)

I’m taking it this semester and it is a fun class. (data)

Next semester it is being taught at the same university, so the information, assignments, and classroom experience will probably be similar to what they are this semester. You and I are friends and have a lot in common, so it is likely we would enjoy the same experiences. (warrant)

That would be both awkward and inefficient. However, if your friend just said the shorter version of the recommendation, what would happen? It is quite possible you might both assume all of the information in the longer version without either of you actually saying it. Or you might ask your friend if the same professor is teaching it next semester. This is actually you questioning their warrant. If the class is being taught by a different professor, it might be very different and the data of their experience from this semester might not tell you much about the class next semester.

Using the Toulmin Model

When creating a presentation, it is important to ask yourself “what are the main things I want my audience to believe after hearing my presentation?” These are your claims. Once you identify them, ask yourself “what data will I need to support my claims?” Remember that different audiences may have different expectations for what counts as reliable evidence, so you should consider what types of data you need for this specific situation. Finally, ask yourself “does the data I found logically support my claims?” If not, you either need to continue looking for data or change your claim.

Occasionally, you may start with a claim you wish to make, set out to find data in support of your claim, and realize that it is very difficult to find any reliable data that support your claim. That is okay. You then need to determine if…

1. There is no reliable data on this topic (which is rare),
2. You are not looking in the right places (this is possible, and you may wish to ask your instructor or a librarian), or
3. There is good data on the topic, but it does not support the claim you wish to make.

This last option is frustrating, but valuable. You’ve learned that something that you thought was true may not be—or at least not in the way you thought. In this situation, you may have to change your claim to fit your data. You may then choose to change your mind entirely (if the data you found convinces you to do so), or you may decide to modify or limit your claim so that it aligns with the data you found. This is actually a good thing. It means you learned something new and refined your thinking.

We once had a student who wanted to give the previously mentioned speech arguing that going to college was a bad financial investment. He knew that this was a controversial claim, and that convincing an audience of students who had chosen to make that investment would require strong data. As he was researching his topic, he recognized that it was easy to find examples of people who had gotten rich despite not going to college. This kind of data was what led him to his opinion in the first place. However, every thorough study he could find on the topic pointed in the opposite direction; they consistently found that people with college degrees generally earn far more money across their lifetimes than those without. He did not want to lie to or mislead the class by leaving out all of the studies on the topic, but he also was not ready to abandon the topic entirely. Instead, he changed his claim to “it is possible to get rich without going to college.” This claim is far less controversial. This more-nuanced claim was much easier to support with the data he found.

 

Logical arguments can be structured in two main ways: deductively or inductively. A deductive argument starts from a general rule or principle and reasons to a specific conclusion. A famous example often used to illustrate deductive arguments is as follows:

All men are mortal

Socrates is a man

Therefore, Socrates is mortal

As you can see, the argument works by establishing a general rule (sometimes called a major premise), showing how it applies to the specific case or situation (called a minor premise), and using this to make a specific judgement (also called a conclusion). In a deductive argument, if the premises are true, the conclusion is certain to be as well.

To convince your audience using a deductive argument, you need to persuade them:

1. That your major premise is true.
2. That it applies in this specific situation.

Imagine you are pulled over and given a speeding ticket for driving 65 miles per hour in a place where the speed limit is 55 miles per hour. The logic for giving you a ticket is straight-forward: Anyone driving over 55 mph in this area will receive a speeding ticket (major premise). You were driving 65 mph (minor premise). Therefore, you will receive a speeding ticket (conclusion). What if you wished to appeal this ticket? How might you do so? Perhaps the speed limit on the highway was recently changed to 65, and the officer was mistaken to write you a ticket. In this case, you would argue against the major premise—the speed limit is actually NOT 55 mph. It is more likely that everyone agrees that the speed limit is 55 mph, and so you would need to challenge the minor premise. Perhaps you could argue that you were actually driving 55 mph, and the officer must have radared a different car. Or you might argue that the radar gun malfunctioned. In either case, you are not challenging the speed limit, but rather arguing that you were not violating it. If you convinced a judge that either premise was wrong, your speeding ticket would likely be rescinded.

You may look at the example deductive argument about Socrates and thought that arguing that way seems overly formal and awkward. Does anyone actually talk like that? Actually, people regularly use deductive arguments. However, like warrants in the previous section, we do not always say all of the premises out loud.

An enthymeme is a kind of deductive argument in which one or more of the premises is left unstated. You might say “This is the United States— our veterans should have access to mental healthcare.” This might not look like a deductive argument. Here you are leaving out the minor premise. In the context of a discussion of the cost of providing that healthcare, the omitted premise might be “The United States is a wealthy country and can easily afford to provide veterans with mental healthcare.” If you are confident that your listener will agree with that omitted premise and automatically fill it in, you may not need to say it.

It is also possible to provide some premises and leave out the conclusion. Imagine if you asked someone if they wanted a hamburger, and they replied “Actually, I’m a vegetarian.” You would take that four-word sentence to mean that they did not want a hamburger, right? But consider all of the premises you recognized that they did NOT say. They actually made— and you immediately understood— two deductive arguments:

Vegetarians do not eat meat (Major premise)

I am a vegetarian (Minor premise—and the only thing they actually said)

Therefore, I do not eat meat. (Conclusion)

That first conclusion then became the general rule for a second deductive argument that you also filled-in for them.

I do not eat meat (Major premise)

A hamburger is meat. (Minor premise)

Therefore, I will not eat a hamburger (Conclusion)

All of this from four words. Using enthymemes can have multiple benefits. First, they allow you to make the argument more quickly and conversationally by not explicitly stating every premise. Consider how much time (and social awkwardness) the person saved by just saying “actually, I’m a vegetarian” rather than stating all of these premises and conclusions. Second, enthymemes can make listeners feel as though they reached the conclusion using their own reasoning. But they only work if the listeners fill in the missing parts in the intended way. This is another reason that knowing your audience is an important part of persuasion. If your audience shares the same values and assumptions as you, then you may be able to leave more of your argument unsaid. However, if you are talking to an audience that you expect will think differently than you, you may need to more carefully state all the parts of your argument.

An inductive argument starts with specific examples and reasons toward a general conclusion.

My first iPhone was reliable.

My current iPhone is reliable.

My sister’s iPhone is reliable.

Therefore, iPhones are reliable.

We engage in inductive reasoning every day. You make assumptions about how people will act based on how they have acted in the past. If you have gotten good food every time you visit a restaurant, you assume they will make good food in the future. If the average temperatures are rising in the United States, France, China, Egypt, and Brazil, you assume temperatures are rising across the entire planet. Humans are remarkably good at observing the world around us, recognizing patterns, and developing theories of how the world works.

If your presentation provides the right information, you can convince your audience to be confident in those conclusions as well. To do so, you need to persuade your audience that your premises are:

1. Sufficient: that you have enough data to support your conclusion
2. Reliable: that your premises are based on accurate information from trustworthy sources
3. Representative: that your data is similar to other data on the topic.

Typically, you will draw upon both deductive and inductive arguments when writing a speech that attempts to persuade an audience. If you know your audience shares a number of important beliefs (for example, if you are members of the same religious organization), it might make sense to start with those shared beliefs as the major premises for your deductive arguments. If you do not know much about your audience’s starting assumptions, or you believe they are likely to be very different from your own, it might make more sense to start with a variety of smaller, less-controversial, observations, and then build inductively toward your intended conclusion.

This chapter provided an introduction to the role of logos in persuasion. The essential elements of logical arguments are claims, data, and warrants. Deductive arguments start from general rules and apply them to specific situations. Inductive arguments start with specific observations and build toward more general rules. Remember that effective use of logos requires analyzing your audience. Different audiences might have different expectations for what evidence persuades them. Knowledge of your audience may allow you to build a deductive argument based in major premises your audience already believes. Or it may allow you to use enthymemes that guide them to reaching the conclusions you want them to reach. The key to effective logos is knowing your audience and developing the right arguments to persuade that audience.