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 one’s 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, one’s 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.