A Quick List of Common Fallacies

1.         Ad Hominem

Attacking the speaker instead of the message.  “Senator Pinko’s ideas on crime are wrong, because he’s a Democrat.”

2.         Equivocation

Where words change meaning from premise to conclusion.  You know what equivocation is, because every dirty joke you’ve ever heard uses it.

For instance,

Premise:

 

I want to see your peacock, cock, cock.  Your peacock, cock.

Conclusion: Gee, Katy Perry must really like birds. [1]

3.         Exclusivity

Exclusivity is an option-limiting fallacy, where people falsely believe that either one option or the other must occur, without realizing both can, or some unstated third option.  For instance, young folks often think that if they don’t get in to ______ school, their lives will be ruined.  They don’t realize that both can occur until the loan bill comes due.

4.         Absence of Evidence

I like to call this the Apple Juice argument:

Why do I only drink apple juice in the mornings?  Because OJ will break into your hotel room and rob you of sports memorabilia at gunpoint.

When I’m teaching, I always laugh and forget why I was making fun of OJ Simpson and have to look back at my notes.  The absence of evidence fallacy is “We couldn’t find enough evidence to convict OJ of murder, so he must not have done it.”  Stated more broadly, just because you have no evidence something is true does not mean it’s false.

5.         Composition

Whole to part: The characteristics of the group are falsely assigned to each member of the group.  American colleges now are 60% female, so each American college student is 60% female.  LGBTQIAXRA is going to have to add a couple more letters.

Part to whole: The characteristics of the individual are falsely assigned to the group.

 

The Rock is often concerned with whether people can smell what he’s cooking, so the WWE must be a nasal health organization.  Or a restaurant.

6.         Circular Reasoning

This is a perennial favorite among logic neophytes.  They all love to find circular reasoning in everything.  It’s actually pretty rare, and blatantly obvious when it occurs.  The best examples, like most other real world logic, come from rap music.

 

“I’m hot because I’m fly.”  Mims.

P: I’m attractive.
C: I’m attractive.

7.         Absolute numbers vs. percentages

Any link between absolute numbers and percentages is suspect.  A larger percentage of a smaller number can still be smaller than a smaller percentage of a larger number; 10% of 1000 is larger than 90% of 100.

8.         Statistical fallacies

Biased sampling and control group issues come up from time to time.  Imagine a study that purports to show that most Americans support a full-scale legalization of marijuana that was solely conducted in Northern California and Boulder.   The sample must be representative of the population it claims.

It also can’t contain any loaded questions, or those that force an assumption on the answerer.  The classic example is “have you stopped beating your wife?”  Oooh!  Double bind.

9.         Correlation vs. causation

Correlation does not imply causation.  Hospitals are full of sick people, so if you go to the hospital you will become sick.

10.       Categorical fallacies

The most common of all, categorical fallacies are anything where the scope changes categories.  These will often manifest in either past/present/future time changes – what happened vs. what will happen – or shifts in probability or prescriptive nature, like can happen vs. should happen vs. will happen.

It is currently noon where I am.  I could make a categorical fallacy argument based on that:

P: The sun is currently out where I am.
C: The sun will always continue to be out where I am.

11.       S/N or Transitive Fallacies

Assuming a sufficient condition is necessary, or vice versa, or incorrectly chaining transitive conditionals.

[1] Note this is an identical equivocal conclusion to that we could have reached from “I Kissed A Girl.”

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3 Comments on “A Quick List of Common Fallacies”

  1. Great post. I do a lesson on logical fallacies with my college freshmen. I just might use this in class sometime!

    • logicate says:

      feel free. make sure to load it up with as much pop music examples as possible. you can also lie to them and tell them you’ll give out extra credit if they sing along with the choruses. works every time.

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