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Logical Errors

That Can Be Hard To Avoid

(and how to avoid them)

Page Index

1. Overview
2. Venerable (Latin) Logical Errors
   Argumentum ad baculum Argumentum ad hominem Argumentum ad populum Argumentum ex nihilo Non sequitur Petitio principi Post hoc ergo propter hoc Stare decisis Tu quoque
3. Less Venerable (English) Logical Errors
   Bad argument fallacy Bifurcation fallacy Correlation & causation fallacy Mistaken reversal fallacy Whataboutism Bothsidesism)

Overview

People tend to reason badly, so badly, that a great many logical errors have long established Latin names. Latin makes them venerable, of course, but they are still stupid.

• Naturally, when you catch yourself making a logical error you immediately rush to correct your reasoning, hoping it won’t end up having cost you too much money.
• If/when somebody else catches you making a logical error, you are acutely embarrassed and feel like an errant fool (unless you are a very difficult person and think you are right even when everybody knows you are wrong).
• If you catch your roommate making a logical error, you either (1) gleefully point it out and win the argument (unless it doesn’t make a difference to anything or (2) wait until you can giggle and gloat when he/she eventually stumbles over it.
• When you notice a politician making a logical error, you shout at the TV and rail against the pretty pass that such people have brought the republic to (and you vote for his/her opponent, unless that would make things even worse).
• When you notice a professor making a logical error —which we know almost never happens— you quietly close your laptop so nobody knows you were looking at this page. But you may want to drop the course.

Whatever the case, you need to know about common logical errors.

Here is an alphabetical list of such idiocies with venerable Latin names, followed by some for which I have not discovered common Latin names. (Readers of this page may also be interested in a page on Quick Essays on Social Theory, especially Interpreting Motivation.)

List I: Venerable Logical Errors (With Latin Names)

Argumentum ad baculum
If you keep saying it’s too hot to work, I’ll fire you and hire somebody else.
1. Argumentum ad baculum (“arguing at the cudgel”) = offering an inducement for agreeing and/or threatening negative consequences for disagreeing, without regard to the logical properties of the position taken.
   For example:
   • “Splitting infinitives is bad because people will think you are uneducated.”
   • “If you plead guilty, you’ll get a shorter sentence that if a jury finds you guilty.”
Argumentum ad hominem
It’s hard to take somebody seriously who’s covered with tattoos.
2. Argumentum ad hominem (“arguing at the person”) = attacking a person’s character or personal characteristics rather than his or her arguments.
   For example:
   • “I suppose somebody with his income would’t know about that.”
   • “It’s just like a man to say something like that.”
   • “He’s a frat boy; I wouldn’t trust him for a minute.”
Argumentum ad populum:
As you can see from its sales, the Harry Potter series is the greatest literary work ever.
3. Argumentum ad populum (“arguing to popular usage”) = arguing that because an opinion is widespread it must be true.
   For example:
   • “Everyone agrees that tax cuts make the world better.”
   • “Most people agree that high levels of student debt don’t really matter because high levels of inflation will quickly wipe them out.”
   
   Sometimes the “populum” is very restricted in order to get a majority within it, falsely suggesting statistical significance. For example:
   • “Two out of three students [in our survey of three] say that Jordan is the world’s most brilliant professor.”
Argumentum ex nihilo:
Your brother is guilty; he has no alibi.
4. Argumentum ex nihilo (= ex silencio) (“arguing from nothing, from silence”) = arguing that a proposition is right because it hasn’t been proven wrong. Sometimes summarized as “the absence of evidence is not evidence of absence.”
   For example:
   • “Nobody could prove to me that he didn’t steal the money; I think he did.”
   • “I say that the body in the tomb of the unknown soldier is my great uncle, and nobody has proved me wrong, so I must be right.”
   • If there had been a burglary, the dog would have barked, but he didn’t.
Non sequitur:
There’s a lot of traffic; people must all be going to church.
5. Non sequitur (“it does not follow”) = intriducing a statement that does not actually have anything to do with its premise (although one may be insinuated).
   For example:
   
   • “She is French and can’t be expected to understand.”
   • “Many visitors to the United States overstay their visas, so we need to build a wall along the Mexican border.”
Petitio principi:
People voted him into office because he was the most popular candidate.
6. Petitio principi “consulting the premise” = assuming as fact what one is trying to discover or demonstrate (= begging the question, or circular reasoning)
   For example:
   • “Athletes are drawn from the healthiest members of the student body. We encourage all students to participate in athletic programs, which can be the basis for their general health and well being. Indeed, studies have shown that athletes are generally healthier than the average of the student body.”
   • “The stock market indexes dropped today, as many investors bought and sold stock for lower prices than yesterday, which tended to put downward pressure on the market as a whole, which, historically, has usually lowered the indexes.”
   • “Defense spending accounts for a very large proportion of the budget because so much of the budget is spent on defense.”
   • “People join cults because they feel something is missing in their lives so this research will study cults to find out what it is that cults provide which causes people to join them.
Post hoc ergo propter hoc:
As soon as he was elected a wealthy donor bought him a mansion.
7. Post hoc ergo propter hoc “after that thing, therefore because of that thing” = arguing that what precedes must be the cause of what follows, even if no mechanism can be adduced by which they may be connected.
   For example:
   • “Immediately after Adelle Weinstein’s election to the Chicago city council, Germany invaded Czechoslovakia, so she must have been responsible.”
Stare decisis:
We can don’t have enough judges to retry a lot of cases just because of somebody inventing a better DNA test, so it’s better just to let the punishments play out.
8. Stare decisis (“to stand by what was decided”) = refusing to overturn an earlier decision because it already exists.
   In law this refers to a court refusing to overturn an earlier decision (called “settled law”), usually in the interest of stability, with occasional exceptions when the earlier decision is very, very clearly outdated or absurd. US Supreme Court justice Louis Brandeis wrote in 1932: “In most matters it is more important that the applicable rule of law be settled than that it be settled right.”
   For example:
   • “It has become clear that you did not kill the duke, but you have already been condemned to death for his murder, so we will execute you anyway.”
   
   In the realm of science or logic, stare decisis refers to sticking to a standing paradigm as long as possible, even in the face of evidence that it is almost certainly wrong. One legitimate reason to do so is that it works much of the time and there is no better paradigm (or no better paradigm in a given context). Another is financial commitment.
   For example:
   • “Glottochronology obviously does not produce a very accurate age estimate, but sometimes it is the best we have, and it is adequate for many purposes.”
   • “Although there are false negatives from rapid antigen tests, the error rate is low and the test is cheap.”
   • “The power-saving setting actually uses more power, but we will ignore that because we have already launched the advertising campaign.”
Tu quoque:
A lot of you also buy a little something for yourselves in order to clean out the budget by the end of fiscal year.
9. Tu quoque (“you’re another”) = arguing that the opponent does the same thing and therefore his or her criticism should be ignored. (In other words, “everybody does it.”)
   For example:
   • “Don’t say I’m drunk; it’s common for people to get a bit tipsy at happy hour; I’ve seen you really plastered in fact.”
   • “You can’t say I’m mean to my dog given how you treat your pig.”

List II: Less Venerable Logical Errors (Without Latin Names)

Bad argument falacy:
They couldn’t prove where the money went, so we think he is honest.
1. Bad argument fallacy = arguing that because an argument is flawed, its conclusion is therefore wrong or that because an argument against a conclusion is poorly made, the conclusion is therefore right
   For Example:
   • “It is wrong for you to blame inflation on the congress; therefore it is caused by the president.”
   • “It is wrong for you to blame inflation on the president; therefore there is no inflation.”
Bifurcation falacy:
Yes or no: Was she rich?
2. Bifurcation fallacy or False dichotomy = asking the listener to select between two options, one or both of which are in fact wrong or dangerously oversimplified, or when there are other logical possibilities or information is lacking. (This is a common idiocy in courts and Congressional hearings.)
   For example:
   • “Are they patriots or are they communists?”
   • “Is orange a kind of blue or is it a kind of pink?”
   • “Was the tornado caused by climate change or not?”
   • “Is China primarily an ally or a competitor?”
   • “Does financial aid go mostly to white students or to black students?”
   • “Do you or do you not agree that the senator is an errant fool? Yes or no!”
   • “If you don't support me, you are my enemy.”
   • “Give me liberty or give me death!”
Correlation & causation fallacy:
Students who take Latin never become juvenile delinquents, so Latin should be a school requirement.
3. Correlation & causation fallacy = arguing that phenomena that co-occur must therefore have a causal relationship in one direction or the other.
   For example:
   • “In our sample, taller students had higher grades, but further research is needed to determine whether growing taller makes people get smarter or whether smart people just tend to grow taller.
Mistaken reversal fallacy:
They never come in on Wednesday; I don’t see them so today must be Wednesday.
4. Mistaken reversal fallacy = arguing that “if A then B” means “if B then A.”
   For example: Premise: “If it is sunny, then they are playing baseball.” This says nothing about what they are doing when it is not sunny.
   • “It is sunny, therefore they are playing baseball. (A so therefore B. True statement.)
   • “If they are not playing baseball, then it is not sunny.” (Not B so therefore not A, True statement, called a contrapositive.)
   
   This does not mean:
   • (Mistaken Reversal = if B then A) “If they are playing baseball, then it is sunny.” (They may play baseball even when it is not sunny.)
   • (Mistaken Negation = if not A then not B) “If it is not sunny, then they are not playing baseball.” (They may play baseball even when it is not sunny.)
Bothsidesism:
There were good guys and bad guys, and both took some knocks, so there is no point in blaming anybody.
5. Whataboutism or Bothsidesism = arguing that the behavior of one party shold be unexamined because another party did something comparable or more extreme.
   For example:
   • “You can’t write me a parking ticket for staying half an hour too long when you didn’t write a ticket to the guy in front of me who was already parked when I got here!”
   • “So what if invading Russian troops killed a lot of Ukrainian civilians? After all, a lot of Russian soldiers died too. Both sides were murderous.”

Now you know.

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