Avoiding Logical Fallacies

Logic can go wrong in many ways. We’ve talked about building logical arguments. Now let’s consider how to avoid building illogical ones. The logical fallacies below can slip into your own and others’ arguments. Learn to identify them.

Distortions in Logic

• Ad hoc reasoning refers to making up dismissive excuses rather than truly engaging an idea. (The Latin words ad hoc mean “for this”—signifying “in this situation” or “making due with whatever is available.”)
  • Librarians argue that the plight of libraries should concern all citizens, but maybe they should listen to their own advice and “shhhhhh!”

    (Instead of engaging the claim, the response dismisses its importance.)

• Ambiguity refers to a statement that can be taken two different ways.
  • You can never have too much water in a nuclear power plant.

    (Does this mean we need to minimize or maximize the amount of water?)

• Bare assertions deny an opposing position by saying “that’s just the way it is.”
  • There will always be poor people, so there’s no point in helping them.

    (This claim dismisses opposition by saying poverty is just a fact of life.)

• Broad generalizations take some cases and apply them to every case. A similar fallacy is the hasty conclusion,which leaps over intervening steps of logic.
  • The news is full of cases of husbands abusing wives. All domestic violence is committed by men.

    (This claim generalizes from some spousal abuse to all domestic violence.)

• Circular reasoning uses its own premise for a conclusion. By starting with the conclusion, the argument has not actually proven anything. (This form is also called a tautology,which is Greek for “the same words.”)
  • During war, Republican presidents lead better than Democrats. When the United States faces a war, it should elect a Republican. That shows that Republicans make better wartime presidents.

    (In place of an argument, the same assertion is made three times.)

• Complex questions phrase an idea in a way that makes it impossible to counter.
  • When will your party stop destroying the country?

    (To answer the question would be to admit to destroying the country.)

• Correlation as causation wrongly asserts that because two things happen at the same time, they have a cause-effect relationship.
  • President Bush was reading to schoolchildren when the attacks of 9/11 took place. If he had been in Washington, the nation would have been safe.

    (This statement incorrectly assumes that the president’s location caused the 9/11 attacks.)

• False analogies compare situations to other situations that are not truly similar.
  • The presidential race is just like voting for the homecoming king; in the end, the winner gets a lot of credit but very little power.

    (This analogy does not accurately represent the process, in which the winner becomes arguably the most powerful person in the world.)

• False causes incorrectly identify the reason that something has happened.
  • Every time the economy worsens, the Fed lowers interest rates. If the Fed just kept rates high, the economy would be fine.

    (This claim swaps the cause and the effect. The worsening economy causes the Fed to lower interest rates, not the other way around.)

• False continuum refers to the idea that two things that are on the same spectrum are actually the same thing.
  • What is the difference between someone who constantly criticizes the government and someone committing treason? There is no difference.

    (This claim ignores the difference between free speech and treason.)

• False dichotomies simplify a complex situation into two extreme choices. This fallacy is also called either/or thinking.
  • Either we renew NASA’s funding at its former levels or the whole agency shuts down.

    (The agency can function on a reduced budget without shutting down.)

• Genetic fallacies assume that the origin of something is analogous to its current significance.
  • The Democratic Party stems from the Democratic-Republican Party of Jefferson in the early 1800s. As a result, Democrats are really Republicans.

    (This statement ignores the long evolution of both parties.)

• Inconsistent criteria occur when what is required in one case is not required in another.
  • Your candidate won’t back down because he is obstinate. Mine won’t back down because he is determined.

    (Both candidates won’t back down, so both should get the same praise or blame.)

• Non sequitur comes from the Latin phrase for “does not follow.”
  • My candidate has less than 6 percent body fat. If he can trim his own fat, he can trim government fat.

    (This statement does not follow. A person’s body fat percentage does not relate to his or her ability to balance governmental budgets.)

• No true Scotsman refers to discounting a counterexample rather than adjusting faulty criteria. It comes from a famous exchange:
  • All Scotsmen are brave. What about Andrew? He’s a coward, and he’s a Scotsman. Then Andrew is no true Scotsman, for all Scotsmen are brave.

    (Instead of changing the false assumption that all Scotsmen are brave, the person discounts the counterexample of cowardly Andrew.)

• Obfuscation uses confusing wording in order to prevent arguments.
  • It behooves all of us to ameliorate deleterious detriments.

    (This statement means “We should get rid of harmful influences,” an idea so obvious that it really doesn’t need to be stated.)

• Oversimplification involves stating a complex situation in simplistic terms.
  • To remove the national debt, the U.S. government can just print however many dollars it needs.

    (This oversimplification ignores the fact that such an act would catastrophically devalue the dollar.)

• Reductio ad absurdum, Latin for “reduce to absurdity,” breaks something down into such small pieces that it no longer makes any sense.
  • If we allow employees choice about when they work, some will decide to work every other minute.

    (This statement applies a reasonable principle to absurd specificity.)

• Slanted language uses unfair terms that skew the discussion.
  • Politicians are crooks, and we can’t allow crooks to make laws.

    (The language in this statement allows for no reasonable discussion.)

• Slippery slope reasoning says that one small change will lead to an unavoidable cascade of terrible consequences. People who use this fallacy may even use the phrase “slippery slope” in their argument.
  • If we grant legal status to illegal immigrants, we’ll have to pardon all illegal activity.

    (Immigration reform does not require pardoning all illegal activity.)

• Straw man reasoning creates a “dummy” argument for an opposing view and refutes it rather than dealing with the true argument of the opposition.
  • My political rival wants to destroy the country and put everyone in prison. I disagree. I think we should save the country and put everyone to work.

    (That a politician wants to destroy the country is a dummy argument.)

Misusing Evidence

• Appeals to hypocrisy say that one’s own guilt can be forgiven because of someone else’s guilt. The Latin term for this fallacy is tu quoque—literally “you, too!”
  • The previous administration spent well beyond the country’s means, so this administration can do the same thing.

    (Someone else’s bad behavior doesn’t justify one’s own bad behavior.)

• Appeals to ignorance say that something is false because no one has proved it, or that something is true because no one has disproved it.
  • Scientists have yet to find life beyond our planet, which proves that life does not exist elsewhere in the universe.

    (Absence of evidence is not evidence of absence.)

• Appeals to pity beg the audience to not make the arguer suffer.
  • I’ve worked hard on this proposal, so you have to accept it.

    (A proposal should be accepted on its own merits, not due to hard work.)

• Appeals to popular sentiment try to sell an idea by connecting it to something that is beloved.
  • For your grandma’s sake, buy Grandma Smith’s All-American Peanut Butter.

    (A sentimental name doesn’t make peanut butter worth buying.)

• Arguments from authority use someone’s position to indicate that something is worthy or unworthy. Often, this appeal uses paid celebrities who actually know little about the issue or product.
  • On my doctor show, I often prescribe Buffervyl, the all-star pain reliever.

    (An actor who plays a doctor is not a medical authority.)

• Arguments from consequence indicate that something must be true because if it were not, terrible things would result. Ignoring a threat does not remove it.
  • The world’s nuclear arsenal must be secure because a rogue nuke would be too horrible to imagine.

    (The horror of the idea does not preclude its possibility.)

• Arguments from incredulity state that something can’t be true because it is hard to believe.
  • The idea that a subatomic particle can be in two places at once is silly.

    (Actually, quantum physicists have proven this idea.)

• Attacks against the person criticize the individual rather than the person’s ideas. The Latin term for this is ad hominem, “to the person.”
  • We can’t agree on Senator Smith’s proposed tax cuts, but we can agree that he needs to get a haircut.

    (This ad hominem attack diverts attention from the real issue: taxes.)

• Bandwagoning argues for something because many other people like it.
  • All of your neighbors get the Times, and you should, too.

    (A stronger argument would focus on the value of the paper.)

• Half-truths distort the issue by telling only part of the story.
  • Every year, thousands of Americans are injured by power tools, so it is time to ban their use.

    (The thousands who are injured are a tiny fraction of the millions who use power tools safely and who rely on them to make a living.)

• Hypothesis contrary to fact forms an argument on the basis of something that didn’t happen. This fallacy is also called “if only” thinking.
  • If only my candidate had won, the economy would be fixed by now.

    (There is no way to prove or disprove what would have happened if the other candidate had won, so the argument is meaningless.)

• Impressing with numbers uses statistics to baffle the audience and into agreeing.
  • A full 64 percent of the 25 percent of Americans who favor an 80-20 split of public/private land in Alaska live at the 70th parallel.

    (The use of numbers baffles the audience into acceptance.)

• Misuse of humor uses a joke to cover up a serious issue.
  • One way to end world hunger would be to require everyone in the world to watch this documentary: They’ll lose their appetite forever.

    (World hunger is a serious problem that shouldn’t be dismissed with a joke.)

• Red herrings distract the audience by using something emotionally charged. This fallacy gets its name from an attempt to throw off scent hounds by dragging a smelly fish across one’s path.
  • The use of child soldiers in many conflicts across the globe is terrible, but not as terrible as seeing a person consumed by the Ebola virus.

    (The Ebola virus, a separate problem, should not be used to distract from the abhorrent use of child soldiers.)

• Threatening is saying that one should accept an argument “or else.”
  • Before you sign that petition, think about the consequences for your family.

    (Threats are never an acceptable form of persuasion.)