Jacob E. Van Vleet - Informal Logical Fallacies: A Brief Guide

INFORMAL LOGICAL FALLACIES

A Brief Guide

Jacob E. Van Vleet

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The age of making distinctions is gone.

Soren Kierkegaard

I wrote this book over a period of five years while teaching logic and critical thinking courses to undergraduate students in the San Francisco Bay Area. I found that logic textbooks created for these classes are usually large and inaccessible to the average reader. Furthermore, most of these textbooks spend a great deal of time covering formal logic rather than informal logic.

Informal Logical Fallacies: A Brief Guide was designed as an accessible supplementary text for logic or critical thinking courses. This book introduces the reader to over forty informal logical fallacies. These fallacies are commonly found in the media today and are often used to propagate fear, blind faith, and submission. For this reason alone, it is important to become aware of informal logical fallacies. It is my sincere hope that this short guide will sharpen the critical thinking skills of all who read it.

Jacob E. Van Vleet
Berkeley, California
July 2010

The word fallacy comes from the Latin word fallacia, meaning trick, deceit, or fraud. A logical fallacy is an argument containing faulty reasoning. There are two types of logical fallacies: formal and informal. A formal logical fallacy is an argument that is flawed due to an error pertaining to the structure of the argument. An informal logical fallacy is an argument that is flawed due to an error pertaining to the content of the argument. This short guide is concerned with informal logical fallacies.

This book divides informal logical fallacies into five categories. First there are linguistic fallacies. These arguments are flawed due to a lack of clarity, as the use of vague or ambiguous terms severely weakens ones argument. Second, there are fallacies of omission. These arguments selectively leave out vital components or misrepresent certain positions in order to convince the listener of the correctness of the conclusion. For example, if certain options are left out of the equation, then the listener may assume that only the options presented are available. Third, there are fallacies of intrusion. These fallacies involve an incorporation of irrelevant material in order to persuade the listener to agree with a particular claim. For example, appeals to fear or pity may convince one to accept a conclusion when these appeals have little or nothing to do with the truth of the conclusion. Fourth, there are fallacies involving built-in assumptions. These arguments contain assumptions about tradition, nature, and other people. Fifth, there are causal fallacies. These arguments rest on a misunderstanding of cause and effect. For example, one might assume that simply because events occur sequentially they are causally related.

There are many kinds of logical fallacies within each of these five categories. Also, it is not uncommon to encounter certain fallacies that fit in more than one category. These will become clear as one reads through the explanations and examples in the following.

There are at least three main reasons for studying informal logical fallacies. First, by becoming aware of fallacies, one will be able to detect poor arguments. This is an invaluably helpful skill that will guide one through a world full of spin, propaganda, and lies.

Second, by studying informal logical fallacies, ones analytical capabilities will increase. This means that one will not only be able to recognize erroneous reasoning but will also be able to think more critically in general. The ability to think critically will help one in every aspect of life.

Finally, by studying informal logical fallacies, one can gain the confidence to challenge lazy assumptions and unquestioned beliefs. This confidence is necessary in order to think for oneself. Only by thinking for oneself will one be able to fully and authentically approach the most important religious, political, and ethical issues of today.

If you cant say it clearly, then you probably dont understand it yourself.

John Searle

This is also known as the whole-to-part fallacy. This argument states that because the whole has a certain characteristic, the parts that make up the whole must also have the same characteristic. In other words, the fallacy of division claims that the whole is always the same as its parts. For example:

1. The Dodgers have an excellent team this year. Therefore, we can safely conclude that every player on the team is excellent.

2. Republicans are in favor of immigration reform. Mr. Thomas is a staunch Republican. Therefore, Mr. Thomas must be in favor of immigration reform.

3. Kay lives in the wealthy part of town. She must be wealthy.

4. Berkeley is a very liberal city. Stan lives in Berkeley. He must be an extremely liberal person.

5. The cake tastes very sweet. All of its ingredients must be sweet.

It is clear that the parts or ingredients of a whole do not necessarily have the same characteristics as the whole itself. When one commits the fallacy of division, one erroneously uses the characteristics of the whole to define or categorize its constituents. Such an argument strays far from clarity, making assumptions about the parts without critically investigating them or considering them individually.

This fallacy is the opposite of the fallacy of division. It is sometimes referred to as the part-to-whole fallacy. The fallacy of composition involves an assumption that the characteristics of the parts are identical to the characteristics of the whole. In other words, the whole is assumed to be composed of identical parts. For example:

1. The woman who rear-ended me was Asian. All Asians must be terrible drivers.

2. Some living creatures exhibit signs of consciousness. Therefore, all living creatures must be conscious.

3. The cake recipe calls for salt. It must be a salty-tasting cake.

4. The terrorists who attacked us were Muslim. Therefore, all Muslims are terrorists.

5. My server at Sals Diner was extremely inefficient. The service at Sals is terrible and I will never go back.

If one ingredient of a recipe has a certain taste, this does not entail that the final product will taste like the ingredient. Likewise, simply because a member of a group or class is a certain way, this does not necessarily mean that the entire group or class is the same. Members of religions, political parties, and ethnic groups are all extremely diverse. However, due to this fallacy, stereotypical ways of thinking are common. We must be aware of stereotypes and other fallacies of composition.