Logical fallacy #5: Post hoc ergo propter hoc ("After this, therefore because of this")

 

                                                 

We might think of this as the "superstition fallacy." It gets its name from a Latin phrase that translates as “after this, therefore because of this.” For example, I might think, “Every time I wear my lucky shoes, I have a great day!” Obviously, my shoes probably aren’t the reason my day goes well. But our minds are always seeking patterns...

 

Definition: Assuming that because B comes after A, A caused B. Of course, sometimes one event really does cause another one that comes later—for example, if I register for a class, and my name later appears on the roll, it’s true that the first event caused the one that came later. But sometimes two events that seem related in time aren’t really related as cause and event. That is, correlation isn’t the same thing as causation.

Examples: 

Angelys writes: I get that post hoc ergo propter hoc every time my dad and I finish washing our cars, because whenever we wash them, that same day it rains! That happens to us very often.

The argument here would be something like, "It rained because I washed my car." Or even, "I shouldn't wash my car because I don't want it to rain." Or the opposite: "If I want it to rain, I should wash my car."

Pennélope writes: I currently work at a retail store and the air conditioner doesn't work properly. It's never cold enough to wear a jacket, still, my first few weeks working, I brought my jacket everyday, just in case. I remember the one day I decided to leave it at home to wash it, I swear instead of arriving at the store that morning I was at the North Pole. It was extremely cold. I kept repeating myself: "Of course, the day I didn't bring my jacket the air conditioner decided to work at it's fullest capacity." 

The argument here, of course, would be something like: "Whether or not I bring my jacket determines how well the AC will work." When we put it like that, we can see the faulty logic clearly.

Both great examples!

Tip: To avoid the post hoc fallacy, the arguer would need to give us some explanation of the process by which the tax increase is supposed to have produced higher crime rates. And that’s what you should do to avoid committing this fallacy: If you say that A causes B, you should have something more to say about how A caused B than just that A came first and B came later.

 

(Credit: The Writing Center, University of North Carolina at Chapel Hill)

Logical fallacy #4: Ad populum

The ad populum fallacy can be summed up this way: 

“Come on, everybody’s doing it!”

The argument here is that you should do something simply because other people are. 

Definition: The Latin name of this fallacy means “to the people.” There are several versions of the ad populum fallacy, but what they all have in common is that in them, the arguer takes advantage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument. One of the most common versions is the bandwagon fallacy, in which the arguer tries to convince the audience to do or believe something because everyone else (supposedly) does.

 

Examples: Pennélope reminds us of "The famous 'mom saying': If everyone is throwing themselves from a precipice, will you do it too?" This saying points out the clear problem with this type of thinking. She also comments, "Just because everyone eats at McDonald's doesn't mean it's healthy for you." The argument here would something like, "You should eat at McDonalds--it must be good for you, because everyone eats there and they aren't dead of heart disease..."

 

Tip: Make sure that you aren’t recommending that your readers believe your conclusion because everyone else believes it, all the cool people believe it, people will like you better if you believe it, and so forth. Keep in mind that the popular opinion is not always the right one.

(Credit: The Writing Center, University of North Carolina at Chapel Hill) 

Writing Response due Monday, September 20, by midnight

Read Kate Murphy, “Do Your Friends Actually Like You?” https://www.nytimes.com/2016/08/07/opinion/sunday/do-your-friends-actually-like-you.html

Note that I also sent the reading via the chat.

Write 1 paragraph: What idea in this essay did you find most interesting, and why? Include a direct quote from the essay and your analysis of it in your response.

Logical fallacy #3: The sunk cost fallacy

 

Definition: The sunk cost fallacy describes our tendency to follow through on an endeavor if we have already invested time, effort, or money into it, whether or not the current costs outweigh the benefits. (https://thedecisionlab.com/biases/the-sunk-cost-fallacy/)

The basic argument that this fallacy contains is: “I already started this, so I might as well keep going.”

Example: Pennélope writes, "A few years ago, my mom bought me a pair of denim pants. The moment I saw them neatly folded and ready to be purchased, I fell in love. When I took them home and tried them on, they didn't fit or look as I wanted them to. Since my mom picked them up, I didn't want to upset her and make her go back to return them. So, I kept using them only to get the money's worth since I didn't fully like how they looked on me."

This is a great example of the sunk cost fallacy. Here the argument is, "Even though I don't really like these pants, because I already invested emotional energy and my mom invested actual money in these pants, I should wear them."

Below is an essay about the sunk cost fallacy that you might find interesting. It contains a number of examples.

"4 Tips for Avoiding the Sunk Cost Fallacy"

Writing response due Monday, September 13, by midnight

                                Lucy Grealy

Read: Lucy Grealy, "Mirrorings" (PDF posted to Moodle and sent via the chat)

Write: 1 paragraph answering the following question: Do you think Grealy’s essay would have been different if it were written by a man, or not? 

Explain your answer making direct reference to the text via a quotation or paraphrase. (A paraphrase is when you put something someone else has written in your own words, following their sentence or sentences closely. A paraphrase is about the same length as the original text.)

This essay has page numbers, so be sure to add the page number associated with your quote in parentheses.

Note that there are no wrong answers to this question.

Logical fallacy #2: The slippery slope

Definition: The arguer claims that a sort of chain reaction, usually ending in some dire consequence, will take place, but there’s really not enough evidence for that assumption. The arguer asserts that if we take even one step onto the “slippery slope,” we will end up sliding all the way to the bottom; he or she assumes we can’t stop partway down the hill. 

This is the typical definition of a slippery slope--that a particular event will start a chain of consequences leading to an undesirable result. A student asked if the slippery slope could lead to an imagined positive outcome. For example, I might get a good grade in one of my law classes and then imagine that I will graduate summa cum laude and get the best score on the bar exam and then become a famous attorney. I don't see why this type of thinking couldn't also be a slippery slope, because the positive consequences I imagine of my one good grade are also completely without evidence!

Tip: Check your argument for chains of consequences, where you say “if A, then B, and if B, then C,” and so forth. Make sure these chains are reasonable.

 

(Credit: Parts of the definition above, and the tip, are courtesy of the Writing Center, University of North Carolina at Chapel Hill.)

Here are a couple of examples, courtesy of a student in my other class: