logical fallacies

begging the question

A logical fallacy that assumes that a statement is true when it actually requires proof. This tactic asks readers to agree that certain points are self-evident when in fact they are not. Example: "Unfair and shortsighted legislation that limits free trade is a threat to the American economy." Restrictions against free trade may or may not be unfair and shortsighted, but emotionally loaded language does not constitute proof. The statement begs the question because it assumes what it should be proving - that legislation that limits free trade is unfair and shortsighted.

misleading statistics

Definition: Although statistics are a powerful form of factual evidence, they can be misrepresented or distorted in an attempt to influence an audience. Example: Women will never be competent firefighters; after all, 50 percent of the women in the city's training program failed the exam. Tip: Here, the writer has neglected to mention that there were only two women in the program. Because this statistic is not based on a large enough sample it cannot be used as evidence to support the argument.

post hoc (also called false cause)

Definition: Assuming that because B comes after A, A caused B. Of course, sometimes one event really does cause another one that comes later - for example, if I register for a class, and my name later appears on the roll, it's true that the first event caused the one that came later. But sometimes two events that seem related in time aren't really related as cause and event. That is, correlation isn't the same thing as causation. Examples: "President Jones raised taxes, and then the rate of violent crime went up. Jones is responsible for the rise in crime." The increase in taxes might or might not be one factor in the rising crime rates, but the argument hasn't shown us that one cause the other. Tip: To avoid the post hoc fallacy, the arguer would need to give us some explanation of the process by which the tax increase is supposed to have produced higher crime rates. And that's what you should do to avoid committing this fallacy: if you say that A causes B, you should have something more to say about how A caused B than just that A came first and B came later.

appeal to ignorance

Definition: In the appeal to ignorance, the arguer basically says, "Look, there's no conclusive evidence on the issue at hand. Therefore, you should accept my conclusion on this issue." Example: "People have been trying for centuries to prove that God exists. But no one has yet been able to prove it. Therefore, God does not exist." Here's an opposing argument that commits the same fallacy: "People have been trying for years to prove that God does not exist. But no one has yet been able to prove it. Therefore, God exists." In each case, the arguer tries to use the lack of evidence as support for a positive claim about the truth of a conclusion. Tip: Look closely at arguments where you point out a lack of evidence and then draw a reasonable conclusion from that lack of evidence.

weak analogy

Definition: Many arguments rely on an analogy between two or more objects, ideas, or situations. If the two things that are being compared aren't really alike in the relevant respects, the analogy is a weak one, and the argument that relies on it commits the fallacy of weak analogy.Although analogies can help explain abstract or unclear ideas,they do not constitute proof. An argument based on an analogy frequently ignores important dissimilarities between the two things being compared. When this occurs, the argument is fallacious. Example: The overcrowded conditions in some parts of our city have forced people together like rats in a cage. Like rats, they will eventually turn on one another, fighting and killing until a balance is restored. It is therefore necessary that we vote to appropriate funds to build low-cost hosing. Tip: No evidence is offered to establish that people behave like rats under these or any other conditions. Just because two things have some characteristics in common, you should not assume they are alike in other respects.

appeal to authority

Definition: Often people will attempt to strengthen an argument with references to experts or famous people. These appeals are valid when the person referred to is an expert in the area being discussed. They are not valid, however, when the individuals cited have no expertise on the issue. Example: According to Diane Sawyer, interest rates will remain low during the next fiscal year. Tip: Although Diane Sawyer is a respected journalist, she is not an expert in business or finance. Therefore, her pronouncements about interest rates are not more than a personal opinion or, at best, an educated guess. There are two easy ways to avoid committing appeal to authority: first, make sure that the authorities you cite are experts on the subject you're discussing. Second, rather than just saying "Dr. Authority believes X, so we should believe it, too," try to explain the reasoning or evidence that the authority used to arrive at his or her opinion. That way, your readers have more to go on than a person's reputation. It also helps to choose authorities who are perceived as fairly neutral or reasonable, rather than people who will be perceived as biased.

straw man

Definition: One way of making our own arguments stronger is to anticipate and respond in advance to the arguments that an opponent might make. In the straw man fallacy, the arguer sets up a weak version of the opponent's position and tries to score points by knocking it down. But just as being able to knock down a straw man (like a scare crow) isn't very impressive, defeating a watered-down version of your opponent's argument isn't very impressive either. Example: "Feminists want to ban all pornography and punish everyone who looks at it! But such harsh measures are surely inappropriate, so the feminists are wrong: porn and its fans should be left in peace." The feminist argument is made weak by being overstated. In fact, most feminists do not propose an outright "ban" on porn or any punishment for those who merely view it or approve of it; often, they propose some restrictions on particular things like child porn, or propose to allow people who are hurt by porn to sue publishers and producers - not viewers - for damages. So the arguer hasn't really scored any points; he or she has just committed a fallacy. Tip: Be charitable to your opponents. State their arguments as strongly, accurately, and sympathetically as possible. If you can knock down even the best version of an opponent's argument, then you've really accomplished something.

appeal to pity

Definition: The appeal to pity takes place when an arguer tries to get people to accept a conclusion by making them feel sorry for someone. Example: "I know the exam is graded based on performance, but you should give me an A. my cat has been sick, my car broke down, and I've had a cold, so it was really hard for me to study!" The information the arguer has given might feel relevant and might even get the audience to consider the conclusion - but the information isn't logically relevant, and so the argument is fallacious. Tip: Make sure that you aren't simply trying to get your audience to agree with you by making them feel sorry for someone.

slippery slope

Definition: The arguer claims that a sort of chain reaction, usually ending in some dire consequence, will take place, but there's really not enough evidence for that assumption. The arguer asserts that if we take even one step onto the "slippery slope," we will end up sliding all the way to the bottom; he or she assumes we can't stop partway down the hill. Example: "Animal experimentation reduces our respect for life. If er don't respect life, we are likely to be more tolerant of violent acts like war and murder. Soon our society will become a battlefield in which everyone constantly fears for their lives. It will be the end of civilization. To prevent this terrible consequence, we should make animal experimentation illegal right now." Since animal experimentation has been legal for some time and civilization has not yet ended, it seems particularly clear that this chain of events won't necessarily take place. Even if we believe that experimenting on animals reduces respect for life, and loss of respect for life makes us more tolerant of violence, that may be the spot on the hillside at which things stop - we may not slide all the way down to the end of civilization. And so we have not yet been given sufficient reason to accept the arguer's conclusion that we must make animal experimentation illegal right now. Like post hoc, slippery slope can be a tricky fallacy to identify, since sometimes a chain of events really can be predicted to follow from a certain action. Here's an example that doesn't seem fallacious: "If I fail English I won't be able to graduate. If I don't graduate, I probably won't be able to get a good job, and I may very well end up doing temp work or flipping burgers for the next year." Tip: Check your argument for chains of consequences, where you say "if A, then B, and if B, then C," and so forth. Make sure these chains are reasonable.

missing the point

Definition: The premises of an argument do support a particular conclusion - but not the conclusion that the arguer actually draws. Example: "The seriousness of a punishment should match the seriousness of the crime. Right now, the punishment for drunk driving may simply be a fine, but drunk driving is a very serious crime that can kill innocent people. So the death penalty should be the punishment for drunk driving." The argument actually supports several conclusions - "The punishment for drunk driving should be very serious," in particular - but it doesn't support the claim that the death penalty, specifically, is warranted. Tip: Separate your premises from your conclusion. Looking at the premises, ask yourself what conclusion an objective person would reach after reading them. Looking at your conclusion, ask yourself what kind of evidence would be required to support such a conclusion, and then see if you've actually given that evidence. Missing the point often occurs when a sweeping or extreme conclusion is being drawn, so be especially careful if you know you're claiming something big.

ad populum

Definition: There are several versions of the ad populum fallacy, but what they all have in common is that in them, the arguer takes advantage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument. One of the most common versions is the bandwagon fallacy, in which the arguer tries to convince the audience to do or believe something because everyone else (supposedly) does. Example: "Gay marriages are just immoral. 70% of Americans think so!" While the opinion of most Americans might be relevant in determining what laws we should have, it certainly doesn't determine what is moral or immoral: there was a time where a substantial number of Americans were in favor of segregation, but their opinion was not evidence that segregation was moral. The arguer is trying to get us to agree with the conclusion by appealing to our desire to fit in with other Americans. Tip: Make sure that you aren't recommending that your readers believe your conclusion because everyone else believes it, all the cool people believe it, people will like you better if you believe it, and so forth. Keep in mind that the popular opinion is not always the right one.

non sequitur

Definition: This fallacy occurs when a statement does not logically follow from a previous statement. Example: Disarmament weakened the United States after World War I. Disarmament also weakened the United States after the Vietnam War. For this reason, the city's efforts to limit gun sales will weaken the United States. Tip: The historical effects of disarmament have nothing to do with current efforts to control the sale of guns. Therefore, the conclusion is non sequitur.

false dichotomy

Definition: This fallacy occurs when a writer suggests that only two alternatives exist even though there may be others. Example: We must choose between life and death, between intervention and genocide. No one can be neutral on this issue. Tip: An argument like this oversimplifies an issue and forces people to choose between extremes instead of exploring more moderate position.

red herring

Definition: This fallacy occurs when the focus of an argument is shifted to divert the audience from the actual issue. Example: The mayor has proposed building a new sports stadium. How can he even consider allocating millions of dollars to this scheme when so many professional athletes are being paid such high salaries? Tip: The focus of this argument should be the merits of the sports stadium. Instead, the writer shifts to the irrelevant issue of athletes' high salaries. Make sure that your evidence is directly related to the argument. Try laying your premises and conclusion out in an outline form. How many issues do you see being raised in your argument? Can you explain how each premise supports the conclusion?

equivocation

Definition: This fallacy occurs when the meaning of a key term changes at some point in an argument. Equivocation makes it seem as if a conclusion follows from premises when it actually does not. Example: "The organizer of the trip said that we were going to eat light, so I brought extra batteries." In Shakespeare's Julius Caesar, Marc Antony refers to the triumvirate as "honorable men." While Marc Antony initially convinces the audience that the men are "honorable," the definition of the word is changed and the meaning of "honorable" equates to lying, murderous and scandalous.

ad hominem and tu quoque

Definition: This fallacy tries to divert attention from the facts of an argument by attacking the motives or character of the person making the argument. Example: The public should not take seriously Dr. Mason's plan for improving county health services. He is a former alcoholic whose wife recently divorced him. Tip: This attack on Dr. Mason's character says nothing about the quality of his plan. Sometimes a connection exists between a person's private and public lives - for example, in a case of conflict of interest. However, no evidence of such a connection is presented here.

hasty generalization

Definition: making assumptions about a whole group or range of cases based on a sample that is inadequate (usually because it is atypical or too small). Stereotypes about people ("librarians are shy and smart," "wealthy people are just snobs") are a common example of the principle underlying hasty generalization. Example: "My roommate said her philosophy class was hard, and the one I'm in is hard, too. All philosophy classes must be hard!" Two people's experiences are, in this case, not enough on which to base a conclusion. Tip: Ask yourself what kind of "sample" you're using: Are you relying on the opinions or experiences of just a few people, or your own experience in just a few situations? If so, consider whether you need more evidence, or perhaps a less sweeping conclusion. (Notice that in the example, the more modest conclusion "Some philosophy classes are hard for some students" would not be a hasty generalization.)

fallacies

Illogical statements that may sound reasonable or true but are actually deceptive and dishonest. When careful readers detect them, such statements can turn even a sympathetic audience against your position.