Dr. Philip N. Howard
University of Washington
A fallacy is an error of reasoning. It can be used against you in an argument, but if you are familiar with them, you will be able to refute the fallacious argument. Likewise, if you are clever, you can use them to convince others. Some arguments contain fallacies of relevance when the premises of an argument are irrelevant to the conclusion. Other arguments contain fallacies of ambiguity when changeable wording in the propositions can suggest more than one meaning in an argument.
Fallacies of Logic
Correlation is not Causation (Post Hoc Ergo Propter Hoc)
When an event happens in close proximity to another event, it is sometimes easy to assume that the first event caused the second. Often, however, there is more than one cause. A common fallacy of this nature is when someone says, “John read this book page. Then John did this awful deed. This book, therefore, must have caused John to do the awful deed.” You may indeed be able to prove that the book caused John to act in a certain ways, but the proof is much more complex and multi-faceted than just noting that one occurred before the other in time. This fallacy can also be used in reverse, to falsely deny any connection between facts: “Student workloads have increased, and the dropout rate has also increased. However, students are also suffering more psychological damage before college. The increased workloads, then, must not be the real source of the problem.” The evidence here suggests that increased workloads are only part of the problem, but it doesn’t dismiss it as a factor in the higher dropout rates. This is the fallacy of false cause, and many of our superstitions stem from the use of this fallacy. "A black cat crossed Joe's path yesterday, and he died last night. The black cat caused Joe's death."
Begging the Question (Petito Principii)
This fallacy happens when the writer treats an arguable proposition as if it were a fact: “Because students are no longer concerned about receiving a broad range of knowledge in college, the university should not require courses outside a student’s major.” This fallacy usually occurs when a writer misreads his discourse community. In some communities, everyone would agree that students no longer want a broad range of knowledge. In most communities, though (such as our class), this assertion would be highly debatable.
time to come in the house now, Billy."
"Because I said so!"
"Because it's time, and I said so."
This fallacy can often take the form of complex questions such as "Have you given up cheating on exams?"
We often generalize in order to prove our points. This is not necessarily bad. We cannot always come up with an absolute, scientific answer (even scientists use generalization to prove their theorems), so we have to gather sufficient data and generalize from that data. These generalizations are only considered fallacies when the sample we take is too small. Using three people who enjoyed COM382 last year does not prove that most students enjoy COM382; you would need a larger sample to make that assertion responsibly. How large a sample you would need depends on your topic and its consequences. This fallacy can also be called a converse accident. That man is an alcoholic. Liquor should be banned."
Circular logic occurs when the reasons you use to support an opinion are simply a restatement of the opinion itself. For example: “To succeed in college, students need to effectively manage their time because success comes from a balance of work and social time.” Essentially this says, “Students need to balance their time because they need to balance their time.” Circular arguments are ineffective because they don’t provide any support for the author’s opinion; they only restate the opinion itself.
Creating a “Straw Man”
This occurs when the author acknowledges an unreasonable counterargument: “Some people might believe that students should spend their whole life studying and absorbing information, but I think that an important part of scholarship is applying that information to one’s own life.” Does anyone really think that students should only absorb information and never think about how to apply it? This fallacy creates the illusion of different opinions on a question at issue, which in turn forces the author to overlook the specific aspects of a topic where real differences of opinion exist. This fallacy can occur in places where an opposing position is only implied, such as an enthymeme. An enthymeme like “People should form their own opinions about their experiences because this will make their experiences more valuable” assumes that someone in the author’s discourse community might argue that people shouldn’t form their own opinions.
Irrelevant Conclusion (Non Sequitur or Ignoratio Elenchi)
This occurs through the (often accidental) omission of information needed to for the reader to make a connection between two ideas. For example, “The candy is a pretty color therefore it must taste good.” The connection between things that are pretty and things which taste good is missing in this argument. In a law court, in attempt to prove that the accused is guilty of theft, the prosecution may argue that theft is a horrible crime for anyone to commit.
Fallacy of Composition
Each part of this stereo weighs under one pound. This is a very light stereo.
Fallacy of Division
Purdue is a great engineering school. Mike went there; he must be a great engineer.
Fallacy of Ignorance (Argumentum ad Ignorantiam)
There is no proof that witches exist; therefore, they do not.
Fallacies of Emotion
Appeal to Tradition
“We've always done it this way. Why do we need to change now?” Discussions of education, especially changes in education, frequently rest on the appeal to tradition. Maybe the old way is better, but if the old way is better you must prove it by a systematic comparison of new versus old. Saying, “We've always done it this way, so this way must be the best way,” is using this emotional fallacy to support your point. This fallacy can also work in reverse, when an author evokes the appeal of the new. According to this thinking, new is always better.
Appeal to Pity (Argumentum ad Misericordiam)
"Your honor, how can the prosecution dare try to send this poor, defenseless child to jail for the murder of his father and mother. Have a heart; the boy is now an orphan."
Appeal to Force (Argumentum ad Bacculum)
"Pay back the loan and 10 % daily interest by Thursday, or be sure that you have you hospital insurance paid up."
Appeal to Popular Opinion (Argumentum ad Populum)
A parent's favorite fallacy: “If everyone else jumped off a cliff,” you may have heard your parents say, “would you join them?” It is also an advertiser's favorite fallacy—“A million users can't be wrong.” This fallacy says that because everyone else is doing it, it must be the best, right, or moral way. Like the appeal to tradition, this doesn't really argue the benefits or risks of a point. "Don't be left out! Buy your Chevette today!"
Fallacies of Authority
Killing the Messenger (Argumentum ad Hominem)
This fallacy disagrees with an argument by attacking the person who makes the argument. When political discussions become vehicles for attacking “feminists” or “conservatives,” they are usually guilty of killing the messenger. These discussions single out people who belong to a certain group or adhere to a certain ideology without ever examining the validity of the thought itself. This kind of fallacy can be done both by insulting someone or by misrepresenting their associations. An abusive example would be "Don't believe anything John says; he's a nerd." A circumstantial example would be "Of course he thinks fraternities are great. He's a Phi Delta."
Faulty Authority (Argumentum ad Vericundiam)
Can someone with a Ph.D. in history really give you good medical advice? Is a television news anchor qualified to give expert opinions on the First Amendment? Is a TV star or pro athlete a good person to ask about the best computer software, insurance, or automobile to buy? The fallacy of faulty authority is when we use someone whose name is familiar or whose credentials might seem relevant to validate an opinion beyond their expertise. It also applies to the staple of advertising, “studies show.” Which studies? Who did them? Faulty authority is often a matter of degrees. For example, as college students you have a certain authority on issues related to college.
This handout describes some of the most common argumentative fallacies and is adapted from http://www.uoregon.edu/~jshaiman/fall03/fallacies.pdf and http://owl.english.purdue.edu/handouts/general/gl_fallacies.html. For real detail on argumentative fallacies and the philosophy of logic, see http://www.nizkor.org/features/fallacies/