PHIL 1500 - Critical Thinking
Unit 3: Diagraming Arguments
Dr. Donald Nute

Unit 3: Analogical Argument

Using Analogies

Analogies are comparisons of one item with or two others. Analogies are used in three different ways.

1. Analogies are used in descriptions: "Breakfast without orange juice is like a day without sunshine."

2. In explanations: "Electrons in an atom are like planets in a solar system, and the nucleus is like the sun the planets orbit."

3. In arguments: "My last car was a Honda. It gave me good gas mileage. I just bought a new Honda. It will probably give me good gas mileage, too."

We will be studying the use of analogies in arguments. Unlike deductively valid arguments, the premises of an analogical argument do not guarantee the truth of the conclusion. They only make it more likely.

Analyzing Analogical Arguments

Like all arguments, an analogical argument offers a reason to accept some conclusion. An analogical argument involves a comparison between two or more persons, objects, situations, etc. An analogical argument has a form something like the following.

a, b, c and x all have the attributes P, Q, and R. a, b, and c also have the attribute S. So x probably has the attribute S as well.

The conclusion of this argument is, of course, that x probably has the attribute S. We call x the target subject or the target entity and we call S the target attribute in the argument. Here x is being compared with a, b, and c. We call the collection a, b, and c the comparison set in the argument. The premise of the argument is that the target subject and everything in the comparison set share the attributes P, Q, and R. We call P, Q, and R the comparison attributes in the argument. So we could rephrase the form of an analogical argument like this.

The target subject shares the comparison attributes with the members of the comparison set. But the members of the comparison set also have the target attribute. So since the target subject is like the members of the comparison set in these other ways, the target subject probably has the target attribute as well.

The first step in evaluating an analogical argument is to determine the target subject, the target attributes, the comparison set, and the comparison attributes for the argument. It is usually easiest to do this if we first determine the conclusion of the argument. The target subject of the argument is the logical subject of the conclusion, which is usually also the grammatical subject. The target attribute is usually given in the grammatical predicate of the conclusion. The comparison set then contains the things that the target subject is being compared with in the argument. And the comparison attributes are those attributes named in the premise of the argument. The premise assumes that we already agree that the target subject and the members of the comparison set all have the comparison attributes.

Here's a concrete example of an analogical argument.

John Grisham's novels The Firm, The Pelican Brief, and A Time to Kill were all made into block-buster movies. They will probably make a block-buster movies out of his latest novel, The Testament.

The conclusion of this argument is that The Testament will become a block-buster movie. The logical subject of the conclusion, and the target subject of the argument, is The Testament. (Note that in this case the target subject is not the grammatical subject.) The target attribute of the argument, is to be a block-buster movie. In the argument, The Testament is compared with The Firm, The Pelican Brief, and A Time to Kill. These three books comprise the comparison set of the argument. And the premise is that all four of these books, both the books in the comparison set and The Testament, are novels by John Grisham. So being a novel by John Grisham is the comparison attribute.

Evaluating Analogical Arguments

Here are some criteria we can use in evaluating the relative strength of analogical arguments.

The larger the comparison set, the stronger the argument. The more things we can name that are like the target subject that also have the target attribute, the more convincing our argument will be. For example, if we can name several other John Grisham novels that became block-buster movies, the more probable it will be that his latest novel will also become a block-buster movie. If we change our premise to "John Grisham's novels The Firm, The Pelican Brief, A Time to Kill, The Client, The Chamber, and Rainmaker were all made into block-buster movies.", this strengthens the argument.
The more comparison attributes, the stronger the argument. The more ways we know the target subject is like the members of the comparison set, the more probable it will be that it is also like the members of the comparison set in having the target attribute. If we change our premise to "John Grisham's novels The Firm, The Pelican Brief, A Time to Kill, The Client, The Chamber, and Rainmaker were all made into block-buster movies", this strengthens the argument.
The more differences there are between the members of the comparison set, the stronger the argument. Suppose the members of the comparison set are quite different except that they all have the comparison attributes. Then any ways the target subject may be different from the members of the comparison set are less likely to be important in determining whether the target subject will share the target attribute with the members of the comparison set. If we change our premise to "John Grisham's novels The Firm, The Pelican Brief, and A Time to Kill were all made into block-buster movies. The first was about organized crime, the second was about a conspiracy within the government, and the third was about a poor southern African-American who killed the man who raped his daughter.", this strengthens the argument. The Testament will not be exactly like Grisham's other novels that were made into block-buster movies. The more variety there is in the stories in those other novels, the less important it will be for our conclusion that the story in the latest novel is different from those in the earlier books.
The stronger the target attribute, the weaker the argument. A strong target attribute means that the conclusion is making a strong claim. The stronger claim we make in our conclusion in any argument, the stronger evidence we need to support our claim. So if the premises are the same, then they support a weaker conclusion better than a stronger one. In our example, the claim that The Testament will become a block-buster movie is a pretty strong claim. We could weaken it if we just claimed that The Testament will become a movie. By weakening the target attribute, and thus the conclusion, we would produce a stronger argument.
Disanalogies weaken an analogical argument. A disanalogy is a way that the target subject is different from the members of the comparison set. Disanalogies are most damaging when the difference is one that is particularly relevant to the comparison attribute. For example, suppose that someone were to point out that The Firm, The Pelican Brief, and A Time to Kill were all best-sellers, but that The Testament was not selling well. How well a book sells is certainly relevant to the decision whether to make a movie of it. So this would be an important disanalogy between the Grisham novels in the comparison set and The Testament. Looking for disanalogies is an important part of evaluating an analogical argument. Of course, no two things are exactly alike and it will always be possible to find some ways that the target subject is different from the members of the comparison set in an analogical argument. For example, it might turn out that there was a picture of the author on the back of all four of these novels, and that Grisham was wearing a coat and tie in the photo on The Firm, The Pelican Brief, and A Time to Kill, but he was wearing a sweater in the photo on The Testament. But this is hardly relevant to whether the book will be made into a movie and does not weaken the argument.
The more relevant the comparison attributes are to the target attribute, the stronger the argument. And of course, the less relevant the comparison attributes are, the weaker the argument. If we change our premise to "The novels The Firm, The Pelican Brief, A Time to Kill were all sold at Barnes and Noble, and they were all made into block-buster movies", this weakens the argument. A large book seller like Barnes and Noble tries to carry the broadest selection of books possible. That they carry a particular book is not very relevant to whether that book is made into a movie. For example, they certainly carry Webster's New Collegiate Dictionary and Windows 98 for Idiots, but it's pretty unlikely either of these will be made into a movie! That all the books mentioned in the premise of our analogical argument were written by the same author seems much more relevant when we think about whether another book will be made into a movie.

The Fallacy of False Analogy

We say that someone commits the fallacy of false analogy when they make a weak analogical argument of a particular sort. The kind of analogical argument that is usually identified as a false analogy is one where there is a glaring disanalogy between the target subject and the members of the comparison set. Here is an example.

It is cruel to encourage the suffering of unwanted and abandoned puppies and kittens. That is why we spay or neuter our pets. But surely people are more important than pets, and the suffering of an unwanted and abandoned child is far worse than the suffering of a dog or cat. If we sterilize our pets to prevent suffering, then we can surely do no less for the poor and homeless.

This argument is disturbing and distasteful. It is also a false analogy - an extremely weak argument. But what makes it so weak? First, let's analyze the argument. The target subject is poor and homeless people and the comparison set is pets. The comparison attribute is that both poor and homeless people and pets may produce offspring that suffer because they are unwanted and abandoned. The target attribute is that we should sterilize to prevent this suffering. But the problem with the argument is that there is a glaring disanalogy between pets and people. People, whether or not they are poor or homeless, are autonomous agents with certain rights. We do not have the moral authority to make certain choices for them. But we have not only the authority but the responsibility to make these same choices for our pets. These differences are highly relevant to the question whether we can prescribe sterilization for these two groups. Dogs and cats do not understand the consequences of their sexual behavior; they are incapable of making choices based on the consequences of their actions. People do and can. We do not take away the autonomy of a dog or a cat when we make a choice for it that it is incapable of making. We do take away the autonomy of a person if we forcibly sterilize him or her. Thus we have phrases like, "we're comparing apples and oranges." That means any argument based on the comparison would be a false analogy.

Using Analogies to Criticize Arguments

One important ways analogical arguments are used is to respond to other arguments. We often try to show that an argument is a bad argument by showing that is resembles another argument that everyone would agree is a bad argument. The resemblance will normally be in the form of the argument. Let's take an example. Here's the original argument, a case of affirming the consequent.

If Jones had robbed the liquor store, he would have run from the police. Jones ran from the police. So he probably robbed the liquor store.

Faced with an argument like this, we might try to persuade the person who made it that their conclusion is not supported by their premise by giving an example of another case of affirming the consequent where the premises seem reasonable but the conclusion is clearly absurd. Here is an example.

That doesn't follow. That's like saying, "If Jones took birth control pills, he wouldn't be pregnant. Jones isn't pregnant. So he probably takes birth control pills."

The response is an analogical argument. The target subject is the argument about Jones running from the police. The comparison set consists just of the argument about Jones and the birth control pills. The comparison attribute is that these two arguments have the same form. The target attribute is that the premise of the argument does not support the conclusion.

Exercises

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