Friday, July 24, 2015

Common Logical Fallacies

1. Anecdotal Evidence
Using a personal story or isolated example as evidence, commonly used to dismiss statistics. An anecdote is a good way to prove a possibility, but cannot prove a probability.


Example: "This very expensive GLOBAL WARMING bullshit has got to stop. Our planet is freezing, record low temps, and our GW scientists are stuck in ice." ––Donald Trump, in a tweet.

Reality: ". . . global warming means that the globe--i.e., the whole planet, not just where you live--is steadily increasing in temperature, on average. The fact that it is very cold in one small part of the world for a short period of time does not disprove a long-term global trend." ––Emily Atkin, from "Yes, It's Cold. Global Warming Is Still Real", on, Jan 8, 2015

2. An Appeal to Emotion
This is when someone tries to force an emotional reaction, in place of a logical argument. These tactics can focus on fear, hate, guilt, or even pity.

Example: "You don't know how lucky you are to have such a wonderful school here. Think of the children in Africa who can't go to school, because it's not safe."

Reality: Regardless of the situation in some parts of Africa or elsewhere, it doesn't mean we should automatically be happy with our school.

Another common example is when someone shows you a photo or video clip that makes you angry, scared, or sad, but you don't know who's in the photo or video, where they're from, when it was made, or why the people were doing what they were doing. The images make you react without having all the facts.

NOTE: Just because an argument is emotional, doesn't mean it's illogical. If you do something wrong and your parents lecture you about why it was wrong, and make you feel guilty - that's not illogical. That's reality. The problem is when people use these kinds of tactics while being dishonest, in order to manipulate you.

3. Begging the Question (It means taking for granted)
This is when you base your argument on an assumption that may be false.

Example: Apples are healthy because they grow on trees.

Reality: Chinaberry tree fruit also grows on trees, but is poisonous. If you want to prove apples are healthy, you'll need a better argument.

4. Evading the Question (to evade means run from)
Some questions are hard to answer, and so people avoid answering in a number of ways. This is common with politicians. Some simply smile and walk away. Some openly refuse to answer, saying it's none of your business (and sometimes, they're right). The most deceptive, and successful, will choose a new question, and answer that.

Example: "Shouldn't minorities be allowed to purchase homes in white neighbourhoods?"

The politician answers: "Homeowners have a right to protect the value of their property."

Reality: This politician has ignored the rights of minorities, instead pandering to a common fear of white suburban voters (and a corrupt system that devalues homes in minority neighbourhoods), which has been an ongoing issue in America for over a hundred years now.

5. Ad Hominem Attack
This is another way to evade the question, by attacking and insulting the questioner. It asks the question, "Why should anyone ever listen to you?"

This includes name calling, but can be more psychological:

Frank Sinatra on Robert Redford: “Well at least he has found his true love – what a pity he can’t marry himself.”

Examples: "A doctor tells her patient to lose weight, and the patient thinks: “If my doctor really believed that, she wouldn’t be so fat.” A movie aficionado pans [skips] the latest Tom Cruise flick because Cruise is a Scientologist. A home­owner ignores a neighbor’s advice on lawn care because the neighbor is a ... you name it: Democrat, ­Re­publican, Christian or atheist." from "Character Attacks: How to Properly Apply the Ad Hominem", Scientific American, June/July 2008

6. Guilt by Association
This is a special kind of Ad Hominem, when you discredit one person for being friends with someone else who is scandalous.

Example: Many republicans criticized Barack Obama for befriending Bill Ayers, who at one time committed acts of terrorism in the US. Sarah Palin claimed he was, "palling around with terrorists."

Reality: Bill Ayers coordinated a series of bombings in Chicago, as an anti-Vietnam War protest in the 1960's and 70's (When Obama was a teen, living in Hawaii). Ayers was never imprisoned, due to the FBI's illegal methods of investigation. Since then, Mr. Ayers stopped these acts of terrorism, dedicating his life to teaching. He became a professor at the University of Illinois at Chicago, and was Chicago's citizen of the year in 1997. Besides all this, he was in fact, not a close friend to Obama.

7. Ad Populum
When you direct your insult at a large group of people, it becomes Ad Populum, in other words discrimination (also called a Hasty or Sweeping Generalization). This includes any insults aimed at minorities, ethnicities, religions, skin colour, men, women, children, the elderly, the disabled, etc.

 8. A Non Sequitur:
"When a train of thought proceeds from A to B and back again to Q." ––Bill Griffith
A non sequitur seeks to draw a conclusion from two facts that have no logical connection. Ad hominems, besides evading the questions, are also non sequiturs.

Example: "He's the most popular student, he should be the school president."

Reality: Popularity does not ensure competence. While charisma is an important attribute, it is not the only important attribute, whether in politics or elsewhere, so it doesn't make him the obvious choice.

Non Sequiturs can be really funny when obvious:

But, non sequiturs can be especially difficult to spot, because they often feel right.

Example: "Penelope Cruz uses L’Oreal hair colour.  I should use it, too, so my hair will look as good as hers."

Reality: Using this product is no guarantee your hair will look like Cruz's, especially when you have different genes.

9. Post Hoc, Ergo Propter Hoc (False Causation)

"OBSERVATION: I have never been in a bad mood and near a beach ball at the same time. Causation? Correlation? Or fate?" - Demetri Martin

This is a non sequitur of events. Scientists get headaches over this one, constantly repeating, "correlation does not equal causation."

Example: Someone eats an ice cream cone on a cold day and gets a sore throat the next day. His mother says, "You shouldn't have eaten that ice cream!"

Reality: Hey, maybe the cold ice cream did upset his throat. Or, maybe it's a virus he picked up at work, or when he bought that cantaloupe at the supermarket which someone else had sneezed on.

Also, every good-luck charm is a post hoc fallacy.

10. Oversimplification
This is when you simplify an argument to such a degree that crucial facts are missing.

Example: "The Titanic is a film about an elderly survivor who recounts her tale of how a poor boy once nailed her in the backseat of a car."

Reality: The story is about more than that. Note, oversimplification may not be true, but it makes for good humour.

11. False Dichotomy (The Black & White Fallacy)
This is a special kind of oversimplification, when you twist an argument down to two options, when in fact there are more alternatives. False dichotomies can take an either-or form:

Example: "You're either with the president, or you're against him.
Reality: You could be neutral to the president, neither for nor against.

They can also take an if-then format:

Example: "If I work harder at my singing, I should win the contest!
Reality: You might win, but you just don't know until you hear the competitors.

Sometimes someone will make it three options, instead of two:

Example: C.S. Lewis once said Jesus was either the Son of God, a liar, or a madman. There are no other options.
Reality: This argument hinges on the accuracy of what we know about Jesus from the Bible. Assuming the Bible is 100% accurate Begs the Question.

12. The Middle Ground Fallacy
This is a special false dichotomy where, instead of insisting there are only 2 (or three) options, one argues that the only true answer between two opposing viewpoints must be a compromise.

Example: Molly says that vaccinations cause autism in children, while her scientifically well-read friend Heather says this was proven false. Their friend Jennifer suggests a compromise that vaccinations might cause autism, but only sometimes.

Reality: While the jury is still out on the true cause/s of autism, statistics show no significance between the disease and vaccinations, whatsoever. There's no logical basis for a compromise here.

13.  Argumentum Ad Ignoratum
This is when you make an argument based on ignorance. Since the opposition doesn't have an answer or solution, your answer must be right.

Example: UFO's exist because no one's proven they don't. Also, Ghost don't exist because no one has proven they do.

Reality: Lack of proof is not proof.

14. The Bandwagon
This is when you accept the practices of a group as both normal and ethical. Anything unaccepted by the majority, must therefore be unethical.

Example: Slavery was considered acceptable for hundreds of years simply because, hey, everybody's doing it.

15. The Trick Question
This is a logic trap, meant to trick the opposition into saying something foolish. It's a "gotcha" question.

Example: "So, have you stopped beating your wife?"
If you say yes: You just admitted to beating your wife.
If you say no: You're still beating your wife.
In Reality: Hopefully, you've never beaten anyone, especially your wife.

Another Example: "How do you spell HIV?"
You answer: "H-I-V."
The Trick Question: "Are you positive?"

16. Burden of Proof Reversal
Normally, when someone makes a bold claim, such as a cure for cancer, the burden is on them to prove it. When this person tries to shift that burden to the skeptics, it's illogical.

Example: Bill says he has an invisible friend whose pixie dust cures cancer and reverses aging. Since you can't see this friend, you can't deny it, even though Bill doesn't look any younger, and he still has cancer.

17. Slippery Slope
This fallacy, a kind of fear tactic, states that if we allow one thing to happen, it will automatically lead to other things we don't want.

Example: Some claim that if same-sex marriage is legalized, it will lead to polygamy, as well as marrying family members, animals, and even cars. Others have claimed that, if marijuana were legalized, it would become a gateway drug, increasing abuse of cocaine, meth, and heroin. In American politics, some people advocated a "domino theory" that if we allowed one country, like Vietnam, to become communist, that many more would follow. Today, it's still used to defend America's 2nd amendment, the right to own guns. People say if gun owners needed to pass background checks, or wait a week before buying a gun, it's a slippery slope towards gun confiscation and an Orwellian dystopia.

18. Personal Incredulity
This is when someone refuses to believe an argument because they don't understand it, or find it hard to believe.

Example: Some people still refuse to accept the evolutionary principles that mutated apes into humans, because we look so different.

19. The Gambler's Fallacy
This is the belief that good and bad luck come in "runs".

Example: "The ball has just landed on red at the roulette table 6 times in a row! There's no possible way it could happen a 7th time! What are the odds of that?"

Reality: While the odds of predicting 7 hits on red may be slim, if you spin that wheel again, the odds are still 50/50 of it landing on red, just like the first time you spun the wheel.

20. The No True Scotsman Fallacy
This is when you change your argument with additional stipulations, when you realize you've lost the debate (Note, the name of this fallacy is an Ad Populum attack on the Scottish).

Example: Angus says, "No Scotsman puts sugar in his porridge."
                 His friend Lachlin says, "Hey, I put sugar in my porridge."
                 Angus retorts, "No true Scotsman puts sugar in his porridge."

21. An Appeal to Nature
This is when someone uses nature as an ideal to justify some things, while vilifying others. If something is unnatural, it must be bad.

Example: Some people warn against modern medicine, saying "natural alternatives" are better, even though they're not scientifically tested. Some people say marijuana is safe because it's a natural drug. Some reject homosexuality saying it's not natural. Every time I hear this I think of lions eating gazelles, and sharks eating seals, and wonder where the ethics is in that.

22. An Appeal to Authority
This is when you quote a well respected person, or people, as evidence for your thesis. This is a common argument, and often perfectly reasonable. But, there are five dangers.

      1. Your authority could be wrong. I'm sure someone once quoted pope Urban VIII in saying the
          earth was the center of the universe. And why was this pope wrong? Because astronomy was
          outside his field of expertise. It makes perfect sense to quote an expert in his/her field, like
          Einstein with physics, but start quoting him on other topics, like genetics or medicine, and his
          authority quickly fades - plus you'll find there's not much material to quote.

     2. The authority may have since changed his/her mind. It does no good to quote someone who
         later claims he/she was wrong.

     3. You may have misunderstood the quote. You thought it meant something else. A common
         example is when people quote Picasso, who said, "Art is a lie that tells the truth," and call him a

     4. You may be quoting your authority out of context. The quote you found may support your
         argument, but check to see if this expert didn't say still more that refutes it. This is especially
         common with quotes on DVD boxes.

Example: The DVD for Live Free or Die Hard quotes the New York Daily News as saying, "Hysterically...entertaining."

The Full Quote: "The action in this fast-paced, hysterically overproduced and surprisingly entertaining film is as realistic as a Road Runner cartoon."

     5. The authority might lose his/her reputation. Many famous people fall from grace due to
         scandal. I'm sure Bill Cosby gave lots of great advice to young comedians, and even parents,
         but who cares? The guy's a rapist, and now that it's publicly known, no one's ever going to listen
         to him again. This is a risk you run anytime you use someone's fame and reputation as an

23. The Straw Man Fallacy
Sometimes someone will take a quote out of context in order to attack an argument. It's a kind of deception. You change your opponent's argument to make it easier to beat. Republicans loved to use this quote, which made Barack Obama seem anti-business.

Example: "If you've got a business––you didn't build that. Somebody else made that happen."

The Full Quote: "If you were successful, somebody along the line gave you some help. There was a great teacher somewhere in your life. Somebody helped to create this unbelievable American system that we have that allowed you to thrive. Somebody invested in roads and bridges. If you've got a business––you didn't build that. Somebody else made that happen. The Internet didn't get invented on its own. Government research created the Internet so that all the companies could make money off the Internet."
"The point is, is that when we succeed, we succeed because of our individual initiative, but also because we do things together. There are some things, just like fighting fires, we don't do on our own."

In the full quote, we see that Mr. Obama was really arguing that everyone has a responsibility to give back to the community, through taxes, charity, etc.

24. An Appeal to the Highest Authority
Finally, some people like to think they know exactly what God is thinking, and will use it in an argument.

Example: "God's still up there. The arrogance of people to think that we, human beings, would be able to change what HE is doing in the climate is to me outrageous" ––James Inhofe, US Senator from Oklahoma, and chairman of the Senate Environment Committee, on why he doesn't believe in climate change.

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