- Explain common logical fallacies
- Differentiate between types of logical fallacies
A logical fallacy is a flaw in reasoning or a flawed structure that undermines the validity of an argument. A fallacious argument can make productive conversation impossible. Logical fallacies are often used by politicians and the media to fool people because they have the deceptive appearance of being reasonable—despite their exploitation of our emotional, intellectual, and psychological weaknesses. Having the ability to recognize fallacies in an argument is one way to reduce the likelihood of such occurrences in your own writing.
This videos walks you through techniques for evaluating an argument and looks at some common fallacies.
You can view the transcript for “Evaluating an Argument” here (opens in new window).
Some of the most common types of logical fallacies are discussed below. Read each one carefully, then try to come up with your own example of how you’ve seen that fallacy. First are some fallacies that misuse appeals to logos or attempt to manipulate the logic of an argument:
Fallacies related to logos
|Hasty generalization||jumping to conclusions based upon an unrepresentative sample or insufficient evidence.||“10 of the last 14 National Spelling Bee Champions have been Indian American. Indian Americans must all be great spellers!” OR Example: “Some teenagers in our community recently vandalized the park downtown. Teenagers are so irresponsible and destructive.”|
|Appeal to ignorance—true believer’s form||arguing along the lines that if an opponent can’t prove something isn’t the case, then it is reasonable to believe that it is the case; transfers the burden of proof away from the person making the claim (the proponent).||“You can’t prove that extraterrestrials haven’t visited earth, so it is reasonable to believe that they have visited earth.”|
|Appeal to ignorance—skeptic’s form||confusing absence of evidence with evidence of absence; assumes that if you cannot now prove something exists, then it is shown that it doesn’t exist.||“There’s no proof that starting classes later in the day will improve the performance of our high school students; therefore, this change in schedule will not work.”|
|Begging the question||circular argument because the premise is the same as the claim that you are trying to prove.||“This legislation is sinful because it is the wrong thing to do.”|
|False dilemma or false dichotomy||misuse of the either/or argument; presenting only two options when other choices exist||“Either we pass this ordinance or there will be rioting in the streets.” OR ” If you are not with us, you are against us.”|
|Post hoc ergo propter hoc||Latin phrase meaning “after this, therefore because of this”; confuses correlation with causation by concluding that an event preceding a second event must be the cause of that second event.||“My child was diagnosed with autism after receiving vaccinations. That is proof that vaccines are to blame.” OR “It rained just before the car died. The rain caused the car to break down.”|
|Non sequitur||Latin for “does not follow”; the conclusion cannot be inferred from the premises because there is a break in the logical connection between a claim and the premises that are meant to support it, either because a premise is untrue (or missing) or because the relationship between premises does not support the deduction stated in the claim.||“If she is a Radford student, she is a member of a sorority. She is a Radford student. Therefore she is a member of a sorority.” OR “I hear the rain falling outside my window; therefore, the sun is not shining.”|
|Smoke screen||avoiding the real issue or a tough question by introducing an unrelated topic as a distraction; sometimes called a red herring.||“My opponent says I am weak on crime, but I have been one of the most reliable participants in city council meetings.”|
|Straw man||pretending to criticize an opponent’s position but actually misrepresenting his or her view as simpler and/or more extreme than it is and therefore easier to refute than the original or actual position; unfairly undermines the credibility of claim, if not the source of claim.||“Senator Smith says we should cut back the Defense budget. His position is that we should let down our defenses and just trust our enemies not to attack us!”|
Fallacies related to pathos
See below for the most common fallacies that misuse appeals to pathos, or emotion.
|Appeal to fear||using scare tactics; emphasizing threats or exaggerating possible dangers.||“Without this additional insurance, you could find yourself broke and homeless.” OR “Elizabeth Smith doesn’t understand foreign policy. If you elect Elizabeth Smith as president, we will be attacked by terrorists.”|
|Appeal to guilt/appeal to pity||trying to evoke an emotional reaction that will cause the audience to behave sympathetically even if it means disregarding the issue at hand.||“I know I missed assignments, but if you fail me, I will lose my financial aid and have to drop out.”|
|Slippery Slope||making an unsupported or inadequately supported claim that “One thing inevitably leads to another.” This may be considered a fallacy of logos as well as pathos but is placed in this section because it often is used to evoke the emotion of fear.||“We can’t legalize marijuana; if we do, then the next thing you know people will be strung out on heroin.”|
|Bandwagon||The bandwagon fallacy is also sometimes called the “appeal to common belief” or “appeal to the masses” because it’s all about getting people to do or think something because “everyone else is doing it” or “everything else thinks this.”||“Everyone is getting tattoos in college, so you might as well do it too.”|
Fallacies related to ethos
Beyond lying about their own credentials, authors may employ a number of fallacies to lure you to their point of view. Some of the more common techniques appear in the chart below. When you recognize these fallacies being committed you should question the credibility of the speaker and the legitimacy of the argument.
|Ad Hominem||Attacking the person making an argument rather than the argument itself. Sometimes called name-calling or the personal-attack fallacy.||Of course that doctor advocates vaccination—he probably owns stock in a pharmaceutical company. OR Person 1: “I am for raising the minimum wage in our state.” Person 2: “She is for raising the minimum wage, but she is not even smart enough to run a business.”|
|False Authority||Relying on claims of expertise when the claimed expert (a) lacks adequate background/credentials in the relevant field, (b) departs in major ways from the consensus in the field, or (c) is biased, e.g., has a financial stake in the outcome.||Dr. X is an engineer, and he doesn’t believe in global warming.|
|Guilt by Association||Linking the person making an argument to an unpopular person or group.||My opponent is a card-carrying member of the K.K.K.|
The first step to avoiding logical fallacies in your own writing is learning how to identify them in other writing. You can find examples of logical fallacies on the news, on the internet, and on the street. Sometimes these fallacies are egregious and obvious (think about the headlines you see in the tabloids), but other times the logical issues are less obvious.
In the following exercises, consider the fallacies you have learned about in this section. Try to apply those definitions to the following scenarios. Choose the fallacy that most accurately describes what’s going on in each statement.
In this video example, a student was asked to find logical fallacies in advertisements. Watch to see which fallacies he identifies, and consider if you’ve encountered media making similar arguments.