Common Informal Fallacies
The term “fallacy” is used by some philosophers and rhetoricians only for particular types of errors in deductive and inductive arguments, but others expand the term to include more categories of errors in reasoning, as well as rhetorical (persuasive) techniques that lead to untrustworthy, unsound, and improbable conclusions. Following is a list of some common informal fallacies and examples of faulty reasoning. This list should help you to recognize weaknesses in logic when you encounter them in other people’s arguments and help you to avoid weak and fallacious reasoning in your own arguments and papers.
Most of the following definitions and examples of informal fallacies are from Chapter 5 of Navigating America: “Understanding Argument and Persuasion,” and more fallacies and examples can be found in that chapter. (Other examples and explanations were added after publication.) Some of the examples are somewhat tongue-in-cheek, but I hope that they will still help you understand the basic thought processes embodied in the fallacies.
The Anecdotal Evidence Fallacy occurs when a person ignores or minimizes evidence arrived at by objective and systematic research or scientific testing in favor of one or more personal stories that are unrepresentative. This is also called the confabulation fallacy.
Example: Smoking isn’t going to hurt me—my grandpa smoked three packs a day for sixty-five years and wasn’t sick a day in his life. He lived to be ninety.
Appeal to Authority is the fallacy of saying that simply because an authority supports something, it must be true—or if an authority attacks something, it must be untrue. Experts can disagree. Consider what happens in a trial when one side brings in expert testimony—the other side responds by bringing in experts of their own. You should consult genuine authorities, but you should also examine how they reached their opinions and see if there is consensus in a field. Sadly, some experts allow themselves to be bought, and they will make assertions based on what the people or corporations paying them want disseminated to the public, not what they really believe to be true. In some cases, the so-called “authority” isn’t really an expert in the pertinent field all. Some experts on logical fallacies list as a subcategory the Professor of Nothing fallacy, describing it as trying to add credibility to an argument by quoting a supposed authority who has the title of “professor” or “doctor,” while omitting to mention that the discipline in which the title was earned has little or nothing to do with the subject.
Example: Dr. Butz is a professor and a PhD; thus, he is obviously a highly-educated man, so we should believe him when he says that the Nazis didn’t deliberately exterminate millions of Jews. [Professor Butz is an associate professor of electrical engineering, not a historian.]
Appeal to Belief argues, either explicitly or implicitly, that because “most” people believe something to be true, it must therefore be true (this fallacy is sometimes employed even when the arguer is incorrect about “most” people believing something). It is related to the Appeal to Popularity fallacy.
Example: According to a Harris poll, 84% of people believe in miracles, so we should assume miracles really do occur—that many people can’t be wrong.
Appeal to Consequences is the fallacy that takes the form of saying we should accept conclusions that are psychologically comfortable to us and reject conclusions if they cause us psychological discomfort. We should always consider the consequences of an action, but we need to distinguish between consequences that we can prove to be logically relevant and those that might simply distress some of us.
Example: I don’t believe that human actions contribute to global warming—after all, what can I do about it? And I certainly don’t want to change my lifestyle dramatically. I like the way I live!
Appeal to Ignorance argues that if you cannot prove that something is false, it must be true, or if you cannot prove that something is true, it must be false.
Example: I believe in ghosts—no one has ever been able to prove they don’t exist.
Appeal to Intuition takes the form of believing that because an idea does not match our experience of how things work or how we believe they should work, then that idea is not true. (It also takes the from of believing that what "seems" true must be true.) Essentially, it argues that for something to be accepted as true, it must be similar to what we already believe to be true. Sometimes this fallacy is preceded with phrases like “Common sense tells us that . . . ” or “My gut feeling is that . . . ”
Example: That kid can’t sit still—he has Attention Deficit Hyperactivity Disorder; giving him stimulants can’t possibly help him. [In reality, stimulants are an effective method of treatment for ADHD.]
Appeal to Popularity argues that because most people have favorable emotions toward something, it must be good, or that because most people have unfavorable emotions against something, it must be bad. This fallacy has been used historically to support some pretty heinous actions, including slavery and genocide, and we still see it in operation around the world today. Think about the arguments made for and against some current controversial issues, and you’ll probably be able to come up with a number of examples.
Example: Most people think that it is fine to give up some rights and liberties if it could make us safer, so it is obviously the right course of action.
Begging the Question takes the conclusion of an argument and, instead of offering a genuine premise, simply rephrases the conclusion itself. No matter how strongly you feel about a subject, you should be able to see that a conclusion can’t be supported with itself—it must have distinct premises that aren’t rewordings of the conclusion. We tend to use circular reasoning when we are trying to defend principles that we are so emotionally sure of or have believed for so long and unquestioningly that we cannot conceive of their being false. It is also sometimes called the Vicious Circle.
Example: Gay marriage should not be legalized because marriage should be between a man and a woman.
Common Practice is when you justify something wrong by claiming that a lot of people engage in the same wrong. It dismisses all other relevant factors and asks the audience to accept that something wrong is just, reasonable, or at least excusable because a lot of people engage in the activity. This is an all-too-common justification for reprehensible behavior.
Example: I saved time by copying and pasting some paragraphs from sources I found on the Internet—lots of students do.
Confirmation Bias occurs when a person sees or accepts only the evidence that supports a desired conclusion. This is related to Tainted Sample.
Example: I know he really, really likes me. He said my new haircut looked OK, and he took me to a nice restaurant that didn’t cost me too much money, and he came over to my apartment and stayed over three hours watching the football game, and he said he’ll call me sometime soon. I’ve found Mr. Right!
False Cause, also called Questionable Cause, happens when someone claims that something that follows something else or occurs with it must be caused by it. Sometimes the two are related only coincidentally, or are both caused by something not yet identified. Superstitions, selective perceptions, and selective memory lead to many examples of the False Cause fallacy.
Example: I know that walking under a ladder causes bad luck—I once walked under a ladder, and five weeks later, I lost my wallet. I’m never going to walk under a ladder again.
An example that crops up frequently is when someone who engages in senseless, random violence is found to have liked video games depicting violence, and the playing of these games prior to the incident is then said to be the cause, and then the conclusion is reached that, in general, playing violence-themes video games causes violent behavior. This ignores the hundreds of thousands of people who play such games without ever engaging in violent behavior, and it also ignore the other factors in the life of the person who committed the violent act. This reasoning is related to confirmation bias and appeal to intuition. It is also the result of simply not looking at scientific research--this is all-too-common when people do not develop critical thinking habits and rely on trying to prove that what they already believe is true instead of trying to find out what actually is true.
A False Dilemma is produced when an arguer insists that there are only two possible options available, when there may be three or even more—or when the two choices are not mutually exclusive. It is also called False Dichotomy, the Black and White fallacy, and the Either-Or fallacy.
Example: Either we win the war in Vietnam, or all of Asia will fall to communism.
Invincible Ignorance is the fallacy of insisting on the legitimacy of a position in spite of overwhelming evidence against it. It is closely related to the Slothful Induction fallacy.
Example: Yes, I smoke in my house and in my car with my kids around, but that can’t possibly hurt them—I don’t care what those doctors say.
Shifting the Burden of Proof occurs when someone defends a proposition by demanding that a contrary proposition be proven instead of being able to present arguments in defense of the original proposition. This is related to Appeal to Ignorance and Slothful Induction.
Example: Ghosts exist. If you want to prove me wrong, then you'd better prove what else those eerie sounds that I heard in the graveyard are.
Slippery Slope arguments assert that a sequence of increasingly unacceptable events will inevitably follow from an action or event that may not itself seem undesirable or unreasonable at all, until the arguer takes us all the way to something no reasonable person would want to see occur. False Dilemma ignores middle grounds and alternatives. Slippery Slope acknowledges a middle ground, but moves you from one point at the beginning to an unpleasant extreme at the other end. A may be next to B, and B may be next to C, and so on, but that does not mean that accepting A will inevitably move you to Z.
Example: I could let pay your rent a day late this month without any problem, but next month you’ll want to pay me two days late, and the month after that, you could ask for three, and the next thing I know, you’re going to expect me to wait months for my money.
Slothful Induction is the fallacy of denying the logical conclusion of an inductive argument that presents strong evidence. This fallacy is committed when someone demands an unfairly high amount of evidence before accepting an idea. It is related to Invincible Ignorance and Shifting the Burden of Proof.
Example: I don’t accept what scientists say about climate change—after all, scientific theories are always changing. You can't depend on what scientists say because it may be different next year.
Straw Person fallacies occur when a person attacks an exaggerated, distorted, or false version of an opponent's argument because it is easier than dealing with the real points that the opponent makes. It would be a lot easier to defeat a person made of straw in a fight then a real person—especially a strong one.
Example: My opponent agrees with a federal vaccine advisory panel’s recommendation that all girls and women between the ages of eleven and twenty-six should receive a new vaccine that prevents most cases of cervical cancer. This cancer is related to sexual activity. Encouraging girls as young as eleven to engage in sex is incredibly irresponsible; my opponent is clearly not fit for office.
A Tainted Sample is produced when people collect evidence in a such a way that they are likely to find more evidence in support of their desired conclusions than against them, despite what thorough, objective evidence-gathering would find. This is related to Confirmation Bias.
Example: I can prove my point—I found this great web site that posted dozens of articles that all show that I am right!
Wishful Thinking is when a person accepts a claim as true or rejects it as false merely because he or she strongly wishes a certain conclusion or outcome is true. It is related to Invincible Ignorance and Slothful Induction.
Example: I cannot believe that Thomas Jefferson, one of our history’s greatest men, had slave mistress and had children by her. Some things are simply morally unimaginable and just can’t be true.
A Weak Analogy happens when an argument is based on an analogy that is so weak that the argument is too weak for the purpose to which it is put. For an argument from analogy to be effective, the things being compared should have strongly relevant similarities and no relevant dissimilarities.
Example: Before he married Priscilla, Elvis Presley was asked what he thought about marriage, and he responded with a question: "Why buy the whole cow when you can sneak under the fence?"