If logic was a sport, fallacies would be the fouls or errors. Fallacies violate the rules of logical thought, but often seem plausible or even convincing. If you want your arguments to be logical and well-reasoned, you have to make sure that they aren’t full of logical fallacies.
A fallacy is an illogical conclusion, but not necessarily a false statement. This is an important distinction, discussed further in section XI.
II. A Few Common Fallacies
There are thousands and thousands of logical fallacies, including many that don’t yet have a name. Most deal with very abstract points of logic, causality, and entailment. Here are just a few examples of relatively simple fallacies.
a. Appeal to Popular Opinion
In an argument, have you ever heard someone say “everyone knows” or “9 out of 10 Americans agree”? This is an appeal to popular opinion, and it’s a major logical fallacy. After all, the world is full of popular misconceptions. For example, most Americans believe that Columbus proved the world was round; but actually, this is wrong. That had already been proven thousands of years earlier by the Egyptians, and no educated person in Columbus’ time believed the world was flat.
An appeal to popular opinion is very different from an appeal to expert opinion. If 99 out of 100 geologists agree that earthquakes are caused by tectonic plates, then that’s almost certainly true, because the geologists are experts on the cause of earthquakes. However, the geologists are not experts on Korean history, so we shouldn’t appeal to their opinions on that subject. And the majority if people are not experts on anything other than their own lives and cultures, which means we should only trust popular opinion when those are the subjects at hand. Popular opinion is a fallacious argument; expert opinion is not.
b. Ad Hominem Attack
This is when you attack your opponent as a human being rather than dealing with their arguments. For example: “Einstein here says space-time is a continuum, but he’s a creepy little weirdo with awful hair, so he must be wrong!”
c. False Dichotomy (a.k.a. False Choice or False Binary)
Sometimes a person will present two possible options and argue that we need to choose between them. But this assumes that there is no third option, and that might not be true. For example:
“Either we suppress protesters violently, or there will be chaos in the streets.”
In most cases, such a choice is fallacious: there will be moderate, careful ways to keep the public safe from chaos without any need for violent suppression.
d. Non Sequitur
This is when you draw a conclusion that doesn’t follow logically from the evidence. Sometimes it’s very obvious: “I own a cat; therefore, I work as a computer programmer.” It’s easy to see that the evidence (the pet) doesn’t match the conclusion (the job). However, sometimes the non sequitur is quite subtle, as in the reductio ad Hitlerum.
e. Reductio ad Hitlerum
Despite its comical name, this is a real fallacy that you can see all the time in news media and political debate. A variety of non sequitur, it basically looks like this:
- Hitler did X.
- Therefore, X is evil.
On its surface, the reductio ad Hitlerum can look appealing, and it often persuades people. But think about it: Hitler did many horrible things, but not everything Hitler did was evil. Let’s try filling in the blanks:
- Hitler was a vegetarian.
- Therefore, vegetarianism is evil.
- Hitler had a moustache.
- Therefore, moustaches are evil.
- Hitler was a carbon-based life form.
- Therefore, carbon-based life forms are evil.
Clearly, this line of reasoning doesn’t work at all.
III. The Importance of Fallacies
Fallacies can be very persuasive in spite of being completely illogical. This is because human beings aren’t computers – we think in ways that are more emotional, intuitive, and creative, but less logical. Thus, we often overlook logical fallacies and engage in faulty reasoning as a result. But these failures, while inevitable, can also create problems, especially when we’re engaged in tasks like science and political deliberation, when we need to be as rational as possible and think things through logically. If we fail in our logic, then all our thinking could quickly go astray.
Fallacies, in short, are important because logic is important.
IV. How to Avoid Fallacies
There are hundreds of common logical fallacies out there, and they’re not always easy to spot. That’s why it’s important to get some formal training in rhetoric, logic, or philosophy if you want to argue without accidentally employing fallacies. There’s no step-by-step guide to avoiding all of them, but here are a few tips that you will learn along the way:
- Never try to deceive anyone. If you’re at least trying to make a logical argument, then you can be forgiven for accidentally including a few fallacies.
- Bear in mind that no one can avoid fallacies completely. Even the greatest philosophers of all time were guilty of bad reasoning now and again in their writing. So all you can do is try your best.
- Be skeptical! Try to read your argument with the eyes of a person who does not agree with you. What weaknesses will they find?
- Diagram or outline the steps in your argument. Then examine the gaps between the steps. Ask yourself whether step 2 really follows logically from step 1, and step 3 from step 2. Are there hidden assumptions in your argument that you weren’t aware of?
- Study the known fallacies! As we’ve seen, there are thousands of known logical fallacies, and this article can’t cover all of them. But you can improve your arguments significantly by doing your own research into the logical fallacies and trying to recognize them in your own writing.
V. When to Avoid Fallacies
Fallacies are most important in formal essays and argumentative writing. If logic matters, then it’s important to avoid fallacies. Of course, in many forms of writing, logic doesn’t matter so much. Clearly, fiction and poetry don’t have a logical structure, so fallacies don’t apply. In creative nonfiction, the lines are a little blurrier. You’re supposed to use good reasoning in creative nonfiction, but it doesn’t matter quite so much if you commit a few fallacies along the way. In short, you should be very careful about fallacies in formal writing; in creative nonfiction, you should try to avoid them as well, but you don’t need to worry about them quite so much.
VI. Related Terms (with examples)
People sometimes mistakenly use the word “fallacy” to mean “falsehood” or untrue statement. But a fallacy is not an untrue statement. It’s an illogical inference, but it could still be built out of fully true statements. For example:
- The sky is blue
- July 4th is Independence Day in America
- Therefore, the average human weighs about 135 pounds
All three of these statements are true. However, the “therefore” clearly doesn’t make sense, because statements 1-2 don’t prove statement 3. There are no falsehoods in this argument, but there is a fallacy: specifically, a non-sequitur.
Conversely, a falsehood does not imply a logical fallacy. Here’s a logical argument based on a falsehood:
- Abraham Lincoln was the 14th President of the United States
- James Buchanan was the 15th President of the United States
- Therefore, Abraham Lincoln was president before James Buchanan
This is a logically valid argument with no fallacies. However, premise #1 is a falsehood! Abraham Lincoln was actually the 16th president! If the first premise were true, then the argument would be correct – thus, it’s a logically valid argument. It just so happens, though, that the premise isn’t true, and therefore its conclusion is not true either.
A syllogism is a way of laying out logical deductions in three parts, and this often helps us see whether there are any fallacies involved. The 3-part argument above is an example of a syllogism (and not a very logical one). Here’s a syllogism that is logically sound:
- Cats are mammals
- All mammals are warm-blooded
- Therefore, cats are warm-blooded
Notice how the first two statements act together to prove the third statement. There are no fallacies or falsehoods in this syllogism.
VII. Examples of Fallacies in Philosophy
Many of Plato’s arguments have been deemed fallacious by later philosophers. For example, he bases many of his arguments on the premise that no object can contain opposite properties, e.g. hot and cold or big and small. But this is clearly a false dichotomy. After all, the Earth is very large by some standards (much bigger than us), but very small by other standards (much smaller than the sun). So the same object can have opposite properties given a different frame of reference.
Contemporary philosopher Dan Dennett has also been accused of deploying a false dichotomy in his book Breaking the Spell. In this book, Dennett argues against the belief in God by pointing out that many fundamentalist notions of God are scientifically and philosophically dubious. But Dennett does not take on more sophisticated theologies such as the works of Paul Tillich or Dietrich Bonhoeffer. Thus, he seems to be offering a false dichotomy between atheism and fundamentalism, without considering other possibilities for belief.
VIII. Examples of Fallacies in Popular Culture
Glenn Beck is infamous for his frequent use of reductio ad Hitlerum He frequently points out parallels between Democratic politics and the politics of Germany in the years 1919-1945, covering both Nazi Germany and the Weimar Republic. These parallels are often factually dubious, but even if they are factually accurate this is still a fallacious line of reasoning.
If you want to see ad hominem attacks in action, look no further than the comments on a YouTube video, especially one that deals with politics, religion, or sexuality. People will call each other by some pretty outlandish names on those comment threads, but they rarely engage with the substance of the other person’s argument.