Exposing Faulty Logic

Critical thinking is sorely lacking in our society, yet we seem to have an abundance of faulty logic. It permeates every subject - politics, religion, philosophy, and even science. "Facts" are often based on personal anecdotes, emotional appeal, or stretched analogies. And what's worse, it is nearly impossible to debate any issue with someone who does not see the faults in his own logic.

Faulty logic is so prevalent partly because it isn't often taught in school or at home. Ask most kids if they've ever learned about ad hoc arguments, false analogies or anecdotal evidence and you're likely to get nothing more than puzzled stares and head scratching.

Most people do not learn about the pitfalls of faulty logic until college, if ever. Yet these concepts are simple enough to be introduced to young kids. Here are examples of some common types of faulty logic you may hear when someone is arguing a point:

False Premise

"Americans love country music. It's the logical music choice for any 4th of July party!"

This argument makes the assumption that all Americans love country music. Some Americans like it and others do not. The conclusion that country music is the logical choice is faulty because it is based on the false premise that all Americans love country music.

False Analogy

"Mom and Pop's Online Rare Book Shop should have free shipping. Amazon.com offers free shipping and they are really successful."

A small, individually owned bookstore is not the same thing as a corporate giant. What works for Amazon.com could easily put Mom and Pop out of business. False analogies compare two things that are not similar enough to make a prediction about one based on the results of the other.

Circular Reasoning

"Starbucks coffee is popular because a lot of people really like it."

Popular means that a lot of people like something. You cannot prove your opinion by simply restating it. A logical proof would include facts beyond a definition of popular. You could say that Starbucks coffee is popular because it is routinely chosen in blind taste tests* or because its sales figures are higher than other coffee brands.*

*These are made-up examples, not facts.

Either/Or Fallacy

"I have to wake my daughter up every morning or she will be late for school."

Arguments like this assume that the options presented are the only options, when in fact they are not. The daughter could use an alarm clock, she could wake on her own, or she could get a pet rooster to wake her at dawn. Choosing to ignore the other options does not prove the point.

Appeal to the Wrong Authority

"My mechanic says I should wear magnetic jewelry to stop my joint pain."

A mechanic may be able to reassemble a car, but he is not a doctor. Experts receive specialized training in their field. People who have tried something themselves can have opinions, but they are not experts on the subject.

Post Hoc Fallacy

"I drank 10 glasses of water yesterday and when I woke up this morning the zit on my chin was gone! Water is the best way to clear up acne."

Post hoc, ergo propter hoc is Latin for "After this, therefore because of this." One thing that happens before another did not necessarily cause the second thing to happen. Even if an alarm clock rings every day just before dawn, it is not the reason the sun rises.

Emotional Appeal

"Look at these poor starving children. How can anyone say donating to our charity is not money well spent?"

Arguments that appeal to emotions cloud the issue by making people seem heartless if they disagree. In this example, the charity that claims to help starving children could be woefully mismanaged, in which case a donation to them would not be money well spent.

Anecdotal Evidence

"Orange juice is the healthiest drink ever known! My grandmother drank two glasses of orange juice every day and she lived to be 101."

The story may be true, but it doesn't prove anything. There could be any number of factors that affected the outcome. Also, the experience of only one person (or a small group of people) cannot logically be considered as the "typical" outcome. Until scientific research can back up an anecdotal claim, it is just a hypothesis.

Learning how to understand faulty logic makes it easier to see through illogical arguments. It is an important part of critical thinking, yet one that is sadly overlooked in our current society.


  1. Susan,
    This education is excellent. You are surely correct that most do not receive the fundamentals of logical debate, but make an attempt using many falacies which becomes very frustrating. Thanks.

    One correction if I may. Your definition of "Ad Hoc" is incorrect. Ad Hoc is something in and for itself. For the specific purpose, or situation at hand and for no other purpose: For instance, "A committee formed "ad hoc" to address the issue of salaries."

    Your description is a case of a "non-sequitur" (Latin: It does not follow). An inference or conclusion that does not follow from the premises or evidence. For instance, "You have to love your spouse, because I'm your boss."

    Here's a great place for readers to begin researching logical Fallacies:

    Cheers and great article.

  2. Thanks, Kenny! You are absolutely right. That was supposed to be "post hoc," not "ad hoc." (As you said, the post hoc fallacy is a type of non-sequitur.) I've corrected it in the article. Thanks for the catch! :-)

  3. One of the main reasons why I identify as agnostic and not atheist is because of the Either/Or Fallacy. I've always thought it was ironic that atheists take so much pride in being "rational" when they tend to make this very mistake quite often, pitting evolution against the creation story. Or having proof = it exists and no proof = doesn't exist. Just because you don't have proof of something doesn't mean that it isn't out there and for me, to believe that there could be another answer is what being an agnostic is about - possibilities.

  4. Technically, I consider myself to be an agnostic atheist. Agnostic (not knowing if gods exist) + atheist (not believing in god or gods).

    There is no way to know or prove any supernatural claims, whether they are that gods or unicorns exist. However, I've yet to find compelling evidence to make me forgo reason and believe that either gods or unicorns are anything other than man-made ideas.