Weak Arguments

Arguments that are neither inductively nor deductively strong are weak. Generally, strong arguments are ones that are convincing. The logical structure of the premises supports the conclusion and the audience accepts the premises. So a weak argument is one that fails either logically or the person considering the argument doesn’t accept one or more of the premises.

An argument may be weak, therefore, because it is ill-formed. Or in cases where it is valid or cogent, then it may be weak because you fail to believe that the premises are true. You may disagree with one or more of the premises, or you may be inclined to suspend judgement. If you disagree or suspend judgement about one or more of the premises, then the argument is weak. Obviously, if a premise is given in support of a conclusion, but a person thinks that premise is false, then she shouldn’t accept a conclusion on the basis of it. Claims that you think are false shouldn’t lead you to believe anything else. Consider:

1. If you want to reduce your chances of getting a cold, then you should take Airborne vitamin supplement every day.

2. I want to reduce my chance of getting a cold.

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3. Therefore, I should take Airborne vitamin supplement.

I (Matt McCormick,) think that premise 1) is false. I considered some research and in all the cases that I could find where there was a well-constructed scientific study on Airborne, there was no substantial difference in the rate of people getting colds when they take it. I might discover some new evidence that supports 1), but until then, because those studies failed, and because I’m generally skeptical about alternative medical remedies, I’m going to provisionally conclude that 1) is false. So this argument is weak for me.

Notice that someone else might consider the argument and 1) might seem plausible or true to her. So Elaine, for example, might have taken Airborne and noticed that she didn’t get sick, or she might have heard this claim from several of her friends, so she might believe 1), in which case this argument would be deductively strong for her. So the same argument can be strong for one person and weak for another, depending on their different bodies of evidence and backgrounds.

Even when instead of flatly rejecting a premise, an argument is weak when you’re just not sure. When you suspend judgment about one or more premises, it is weak. If a premise or a piece of evidence or a claim is presented to support a conclusion, but you’re not sure whether it’s true then it can’t be said that the claim supports the conclusion. That argument is weak until you think the premises are true.

There is one more way that an argument might be weak. Cogent arguments are arguments where the premises, if they were true, would make the conclusion likely to be true. But even at their best, these arguments can’t guarantee their conclusion. So there can be cases where an argument is cogent, it has all true premises, but the conclusion still turns out to be false. This is a defeated argument in our terminology.

So an argument can weak one of these ways:

• 1. It is ill-formed.

  2. You think one or more of the premises are false.

  3. You suspend judgment about one or more of the premises.

  4. The argument is defeated.

An argument can be weak for more than one of these reasons too. It might be ill-formed and have false premises, for example.

Here’s an argument that is weak because it is ill-formed.

1. Some of the people coming across the southern border of the United States are illegal immigrants.

2. Some illegal immigrants in the United States engage in criminal activities.

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3. Therefore, the United States needs a fence or wall to prevent illegal immigrants from entering the country.

These premises happen to be true, but is the argument valid? No, the premises, if they were true do not guarantee the conclusion to be true. Is the argument cogent? No, the premises, even if they were true, don’t make the conclusion likely to be true. So the argument is ill-formed. Hence, it is weak.

Here’s another argument that is weak because it is ill-formed:

1. If high schools include sex education into their curriculum, then the teenage pregnancy rate will be comparatively low.

2. The teenage pregnancy rate in Canadian high schools is comparatively low.

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3. Therefore, Canadian high schools must have sex education as part of their curriculum.

This is neither valid, nor cogent. So it is ill-formed. It has the fallacious structure Affirming the Consequent. So, because it is ill-formed, it is weak.

Here’s an argument that is valid, but it is weak for Elaine because of the premises. Her friend Jeffrey does yoga:

1. All people that do yoga are in shape.

2. Jeffrey does yoga.

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3. Therefore, Jeffrey is in shape.

Although the argument has a valid structure, it is weak for Elaine because she does not think premise 1 is true. There are lots of people, in her experience, who do yoga but they are not in shape. She thinks the first premise is false, so the argument is weak.

We’ve also seen that suspending judgment about a premise also makes an argument weak. Elaine considers this argument:

1. If we allow recreational drugs to be bought and sold legally, then more people will do more recreational drugs.

2. If more people do recreational drugs, then more people will commit violent crimes.

3. Colorado allows some recreational drugs to be bought and sold legally.

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4. Therefore, Colorado will have more violent crimes.

Elaine is suspicious about 1. She thinks that a lot of people who want to recreational drugs already do them and mere legalization isn’t going to significantly change the percentage of people who are curious. And she’s not sure about 2 because she thinks that if the drugs are made legal, then a lot of the incentives and black market conditions that contribute to crimes surrounding drugs will be removed. So she doesn’t feel like she has enough information to decide whether the premises are true or false. So the argument is valid, but it is weak for Elaine because she suspends judgement about one or more premises.

And cogent arguments are sometimes weak, even when they have true premises, because they are defeated by a person’s total evidence. Matt goes to a nice restaurant and orders dinner, then he thinks to himself:

1. The vast majority of meat used in American restaurants is produced by inhumane factory factory farming.

2. This steak was used in an American restaurant.

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3. Therefore, this steak was produced by inhumane factory farming.

He feels pretty sure about the truth of 1. Big consumers like McDonald’s and Burger King help make the “majority” claim in 1 true. And 2 is obviously true. But Matt has some important background information. The restaurant is known to use meat from alternative sources; they advertise on their menu that their beef is “sustainably grown,” and “morally raised.” And he doesn’t have any serious reason to think that they are lying. So he thinks that the conclusion is false in this case. This restaurant is one of the ones in the minority left out in premise 1.

Our larger project here has been to recognize and evaluate arguments. We are evaluating them, most generally, into strong and weak categories. Strong arguments, roughly, are ones that give good reasons and employ good logic to support their conclusions, so you should accept them. More specifically, we can now group arguments into:

1) Deductively strong arguments. These arguments are valid, they have true premises, and you should accept their conclusions.

2) Inductively strong arguments. These arguments are cogent, they have true premises, and they are not defeated, so you should accept their conclusions.

3) Weak arguments. These arguments are either ill-formed, they have a premises or premises that are false, 3) they have a premises or premises that you suspend judgment on becasue you're not sure whether they are true or false, or 4) the argument is defeated, in the specific sense defined above.