Logical Fallacies

An anecdote, or personal narrative or testimony about something, can be an effective rhetorical technique. However, this fallacy occurs when the rhetor uses anecdotal evidence to argue against empirical evidence.

Example: Exercise has no effect on your health. My father lived to be 100 years old, and he never exercised in his life. The single example of the rhetor’s father does not counter the much more substantive evidence of exercise’s health benefits.

An anecdote, or personal narrative or testimony about something, can be an effective rhetorical technique. However, this fallacy occurs when the rhetor uses anecdotal evidence to argue against empirical evidence.

Example: Exercise has no effect on your health. My father lived to be 100 years old, and he never exercised in his life. The single example of the rhetor’s father does not counter the much more substantive evidence of exercise’s health benefits.

In this fallacy, also called the burden of proof fallacy, the rhetor argues that the burden is on the opponent to disprove the rhetor’s argument—in other words, the rhetor forces the opponent to “prove a negative,” which is impossible.

Example: No one has proven that Bigfoot doesn’t exist. Therefore, he must exist. Just because no one has proven Bigfoot doesn’t exist does not mean Bigfoot does exist.

In this fallacy, the rhetor attempts to persuade the audience with a form of “peer pressure” by arguing that most other people accept the argument.

Example: Ninety percent of Americans agree with my tax plan. Why don’t you? An argument’s popularity may be evidence of—but is not by itself proof of—the argument’s validity. Perhaps ninety percent of people are simply misinformed?

This fallacy represents a form of circular logic in which the rhetor bases the argument entirely on debatable premises. In other words, the rhetor assumes that the audience agrees with those premises, but the audience may not.

Example: BigBoy bicycles are the best bicycles on the market because they are better than all the rest! The conclusion that “BigBoy bicycles are the best bicycles on the market” assumes that the audience already agrees with the premise that “they are better than all the rest,” but the audience may not agree with that premise.

Analogies, which are comparisons between two things, are potentially effective rhetorical techniques. However, in the false analogy fallacy, the rhetor draws comparisons between two things that are too different to be properly compared—in other words, the rhetor compares “apples to oranges.”

Example: If we can make airplanes, why can’t we make flying cars? Cars are not the same as airplanes, and inventing flying cars would entail much different obstacles than inventing airplanes.

In this fallacy, also called post hoc, ergo propter hoc (Latin for “after this, therefore because of this”), the rhetor falsely assumes that because B happened after or at the same time as A, A must have caused B. The rhetor confuses correlation with causation—just because two things happen together does not mean that one directly causes the other.

Example: We shouldn’t elect people from Brownsville, because every time we do, a hurricane strikes the Gulf Coast. While electing people from Brownsville may correlate with the hurricanes, it does not cause the hurricanes.

In this fallacy, also called the either-or fallacy, the rhetor argues that there are only two possible stances toward an issue when there are actually more than two.

Example: Either you stand with us, or you stand with the enemy. It is possible to fit into neither of these categories—for example, someone could disagree with the actions of “us” while still opposing “the enemy.”

In this fallacy, the rhetor treats two incomparable things as if they were of equal magnitude.

Example: Sure, I plagiarized my paper. But he forgot to cite a quotation! Why aren’t you failing him? Plagiarizing an entire paper is much more severe than forgetting to cite a single quotation, and it therefore warrants a more severe punishment.

In this fallacy, the rhetor assumes that something is “overdue” to happen simply because it has not happened in a long time.

Example: Arkansas has not had a major earthquake in many years. Surely it will have one soon. The odds of an earthquake happening do not increase simply because there has not been one in a while.

In this form of an ad hominem fallacy, the rhetor attacks the opponent’s credibility by connecting the opponent to something or someone with whom the audience is likely to have negative associations.

Example: Senator Stephens’ college roommate was caught using illegal drugs and got kicked out of his dorm. Do you really trust the senator to make good decisions? The roommate’s behavior does not reflect on the senator’s character.

In this fallacy, which is the basis for stereotypes, the rhetor makes an assumption about a group based on a few examples.

Example: I avoid classes taught by young professors. Every young professor I’ve had has been horrible. The young professors encountered by the rhetor are not representative of all young professors.

 Hasty generalizations can also occur when the rhetor makes a conclusion based on too little data.

Example: In 63% of tests, babies were able to identify a C note from a G note. Therefore, babies must have perfect pitch. A success rate of 63% is not high enough to draw this conclusion. In addition, simply being able to distinguish between two different notes is not ample evidence of perfect pitch.

In this fallacy, which is Latin for “it does not follow,” the rhetor draws a conclusion based on irrelevant premises.

Example: Women are physically weaker than men. Therefore, they should not serve in the military. Not all positions in the military demand physical strength. Besides, the rhetor commits a hasty generalization when assuming that all women are physically weaker than men.

As the name implies, in this fallacy, the rhetor overlooks important nuances of an issue or omits potential weaknesses in the argument.

Example: All we need to do in order to pay off the national debt is print 20 trillion dollars in U.S. currency. This solution is too convenient; it overlooks the impracticality and consequences of printing 20 trillion dollars.

This fallacy is named after the red herring fish, whose stench is apparently so strong that it can lead hunting dogs astray. In the red herring, the rhetor attempts to change the subject in hopes that the audience will overlook or forget about a weakness in the rhetor’s argument.

Example: Ladies and gentlemen, I have been accused of blackmailing my opponent. Let me answer these charges by telling you about my service in the military. You’ll be interested to know that I received five distinguished awards for my outstanding service as an infantryman. I was also recognized by the president of the United States for my bravery and heroism. Now, does that sound like a man guilty of blackmail to you? The rhetor attempts to distract the audience from the blackmail charge by telling a long-winded story rather than addressing the charge directly.

In this fallacy, the rhetor argues that one thing will lead to another, which will then lead to another, and so on.

Example: If we cancel class on Friday, then soon students will want us to cancel on Thursday, then Wednesday. Eventually, there won’t even be a school day! Canceling class on one day will not necessarily lead to canceling class on Thursday, which undermines the rest of the rhetor’s argument.

In this fallacy, the rhetor misrepresents the opponent’s argument in order to more easily tear it down—the rhetor builds a “straw man” out of the opponent’s argument.

Example: Those who teach about world religions in school are trying to indoctrinate our children. Do you want your child to be brainwashed? Indoctrination and brainwashing are much easier for the rhetor to attack than teaching world religions, so the rhetor attempts to redefine the opponent’s argument as encouraging these things.

Latin for “you also,” in this type of ad hominem fallacy, the rhetor argues that the opponent’s argument is dismissible because of something the opponent did or said. It is often an attempt to accuse the opponent of hypocrisy.

Example: My opponent wants to increase your taxes, but she didn’t even pay taxes last year! Whether the opponent paid taxes last year does not affect the validity of her argument to raise taxes.