- For Teachers
"Classifying Logical Fallacies: Two Schemes Compared"
In logic and rhetoric, a fallacy is a deliberate or unintentional error in reasoning that results in wrong conclusions. Many logical fallacies exist, and they are all linked to each other because, in the end, they share the common root of faulty logic. The rhetoric textbook Acting on Words (AOW) by David Brundage and Michael Lahey tries to explain ten common logical fallacies and classifies them as either fallacies of oversimplification or fallacies of distortion. On the other hand, Gary N. Curtis, an ontologist, uses a tree diagram to try to link and explain different logical fallacies in his Fallacy Files.
Both AOW's and Curtis's classificatory schemes are useful, but each sometimes is better than the other when it comes to precision in pointing out relationships between particular fallacies or choosing terminology. This essay compares the two presentations of logical fallacies and elaborates on how each classification could be improved by taking some points from the other.
First, both classifications should be categorized taking each other into account. The main difference between the two classificatory schemes is that AOW's divides its ten logical fallacies into only two categories, while the Fallacy Files uses precise taxonomic relations of "parent fallacies" and subfallacies between particular fallacies. The Fallacy Files presents more logical fallacies than AOW, which presents only what the authors of the textbook consider to be the most common ones committed by university students. It is impractical to expect AOW to present less common fallacies, considering the book's specific purpose as a textbook. AOW's simple dichotomous division makes it very clear and easy, especially for first-year rhetoric students using the textbook at university, to understand and remember. The first category of common logical fallacies in AOW's presentation is fallacies of oversimplification. These fallacies all result from failing to see or acknowledge all the dimensions of a situation and thus wrongly reducing complex situations to simple conclusions.
The fallacies of oversimplification all have their equivalents in the Fallacy Files, with some differences in how they are classified and/or named. The six fallacies of oversimplification in AOW's presentation along with their equivalents from the Fallacy Files in brackets are: overgeneralizations (overgeneralities), either/or assumptions (black-or-white fallacies), false analogies (weak analogies), slippery slope assumptions (slippery slope fallacies), assumptions based on events that occurred one after the other or simultaneously (post hoc, ergo propter hoc and cum hoc, ergo propter hoc), and disconnected and circular statements (formal fallacies and circular argument fallacies).
The last fallacy of oversimplification in the list above includes disconnected statements. Disconnected statements are the results of flaws in the basic structure of a deductive argument; the Fallacy Files qualifies the family of disconnected statements as "formal fallacies" and gives examples of the many different kinds of formal fallacies. Examples of formal fallacies (in the terms of the Fallacy Files) are the probabilistic fallacy and the masked man fallacy. In the probabilistic fallacy, the inference that links an argument's premise to the argument's conclusion violates the laws of probability and thus makes the whole argument invalid. In the masked man fallacy, the basic conclusion of an argument becomes invalid when two identical designators in two different contexts in different premises are wrongly substituted for each other in the conclusion. In the Fallacy Files, formal fallacies are distinguished from informal fallacies. Informal fallacies result from something else than the fundamental structure of an argument: they are fallacies related to content. Apart from "disconnected statements", all of the other logical fallacies presented in AOW are informal. It may be that the authors of AOW, who have experience with university teaching, have found that the formal fallacies are not common in student errors. However, it would be good to at least point out the basic difference between formal fallacies and informal fallacies in AOW's description of "disconnected statements". Students should be conscious of the difference between the main deductive structure of an argument, which acts as a skeleton in a human body, and the other parts of an argument, which act as flesh and skin on the skeleton.
In the list of fallacies of oversimplification, AOW's presentation calls a fallacy involving a faulty analogy a "false analogy"while the Fallacy Files calls it a "weak analogy". The Fallacy Files's expositionof this fallacy notesthat while "false analogy" is the most common term, it is a misleading one. According to the Merriam-Webster dictionary, an analogy is a "resemblance in some particulars between things otherwise unlike" or a "comparison based on such resemblance” (Def. 2). If one sticks to this dictionary definition of "analogy", no analogy is "false" because, as will be shown in the example below, it is possible to find commonality between any two things. It should be noted that both the Fallacy Files and AOW also mention that, at some point, all analogies fall apart because each thing is ultimately unique. For instance, some attributes the actor James Dean and the three-toed sloth share are that they are both from the American continent, they are both biologically mammals, and they both have been photographed. Thus, the statement "James Dean had two eyes, just as the three-toed sloth does" does not contain a false analogy, even if the analogy is one that is inappropriate in most contexts. However, the main difference between James Dean and the three-toed sloth is that James Dean is human while the three-toed sloth is not human. Here, the association between James Dean and the three-toed sloth breaks down.