What Is… a Logical Fallacy

Examples of logical fallacies, e.g. ad hominem, begging the question, red herring, straw man

In this series, I dig a little deeper into the meaning of psychology-related terms. This week we’re going to look at logical fallacies.

Logical fallacies are reasoning errors that people make quite commonly when making arguments. While such fallacies don’t necessarily mean that the conclusion is wrong, they’re a weak link in the argument, and they don’t actually do anything to support the conclusion that’s arrived at. These errors are easy to make, and it’s also easy to miss them when other people make them. Being aware of common logical fallacies can help to strengthen your own arguments and make it easier to evaluate others’ arguments.

In this post, when I use the term argument, I’m not referring to people having disagreements and shouting at each other (isn’t that what Twitter is for?); rather, I’m referring to logical arguments, which involve establishing a set of premises and reasoning one’s way to a conclusion.

There are a lot of different logical fallacies that have been identified, and now we’ll take a look at a few of them.

Ad hominem and tu quoque

Ad hominem means against the person, while tu quoque means you too. These arguments involve suggesting that because someone is a bad person, has done bad things, or is hypocritical, their arguments must be wrong. Their arguments may well be wrong, but this is a logical fallacy because criticism of the person is used as a replacement for actually challenging the arguments they’re making.

An example of tu quoque would be if I argued that binge drinking is harmful, and someone called bullshit on that because I’ve binge drank. The fact that I’ve done stupid things in the past does not, in and of itself, mean that the conclusion that binge drinking is harmful is incorrect.

A post on the blog of the American Philosophical Association offers a pure gold example of an ad hominem argument in an interview on Fox News. In it, host Lauren Green interviews Reza Aslan, a religious studies scholar, about his book Zealot: The Life and Time of Jesus of Nazareth. She didn’t seem to have read the book at all, and instead of talking about the book’s actual content, she kept harping about the fact that he was a Muslim, and therefore he shouldn’t be writing about the topic and the book must be fundamentally flawed.

Ad populum

Argumentum ad populum (appeal to the people) is the argument that other people think so, therefore it must be true, or that most people like something, and therefore it must be good. The fact that everyone else is jumping off a cliff does not make for a sound argument as to why you should follow them.

Appeal to improper authority

Appealing to improper authority (argumentum ad verecundium) involves supporting one’s argument by using the opinion of an authority related to something they have no expertise in. Someone with a Ph.D. in history has no reason to have expertise in physics, so if I’m soliciting their opinion on quantum physics and presenting them as an expert because of their Ph.D., then I’m making an appeal to improper authority.

Appeal to ignorance

I would be appealing to ignorance if I pointed out that there’s a lack of evidence regarding a certain issue (e.g. the existence of purple people eaters) and concluded that because of this, you should believe what I have to say about purple people eaters living in the next galaxy over.

A variation of this is the shifting the burden of proof fallacy. When I claim that purple people eaters exist, let’s say you respond that they don’t. I tell you to prove it, which you can’t, because it’s very hard to prove a negative. I then say, “Ha! You can’t prove I’m wrong, so I must be right!” I’ve made my nonsensical claim, but then I’ve shifted the burden of proof over to you to disprove it rather than actually proving it myself.

Appeal to nature

Appealing to nature is the argument that something is “natural”, therefore it must be good/safe. There are plenty of substances in nature that will kill you.

You definitely don’t want to eat blowfish, even if it’s organic, non-GMO, and wild rather than farmed, unless it’s been prepared by someone who knows how to cut out those botulinum toxin-containing natural bits so that you don’t die.

Appeal to tradition

Appeal to tradition is the argument that people have always done A or always believed B, therefore A is correct or B is true. The fact that people have been shaking hands for a very long time doesn’t make for a sound argument that we should be continuing to share germs.

Begging the question

Begging the question (petitio principii) involves skipping over a dubious premise that is assumed to be true. In this way, the person making the argument can slide in controversial bits without proving them and focus on the easier bits.

For example, if I say that euthanasia involves murder and murder is wrong, and therefore euthanasia is wrong, I’ve made the leap from euthanasia to murder and just carried right on along without addressing the question of whether or not euthanasia is murder. That’s a really important piece to have just skimmed over in my argument.

Related to this is circular reasoning, in which each step of an argument relies on the previous step being true, without ever establishing that any particular step is independently true. One example of this is the line of reasoning that God exists because the Bible says God exists, and the Bible is the Word of God, so God exists. Again, the use of this fallacy doesn’t speak to whether the conclusion is true or false. Even if God does exist, circular reasoning would still not be a logical argument to arrive at that conclusion.

Complex question

Complex questions demand a yes or no answer in such a way that, regardless of the answer, answering the question indicates some agreement with an assumption the question is based on.

If I were to ask you if you were high on cocaine when you punched your neighbour, even if you were to answer no, it suggests that you agree that you punched your neighbour.

Equivocation

A lot of words have multiple definitions. Equivocation involves making an argument that incorporates multiple meanings of a word and then suggesting that because something fits meaning A of a word, it also fits meaning B.

For example, the word “right” can be used to refer to something being correct, morally good, or a basic entitlement (as in human rights). If I’m not clear on how I’m using the different senses of the word, I might conclude that something is a right (as in a human right) because it is right (as in correct or morally good).

Similarly, something could be green in colour or green in the sense of being environmentally friendly, but that doesn’t support the argument that something is environmentally friendly because it is green in colour.

Fallacy of reification

The fallacy of reification of treating a word or idea as being equivalent to the actual things that they represent.

I would commit this fallacy if I were to argue that if we can stop people from talking about racism, then racism will cease to exist. Racism is a concrete word that refers to a social phenomenon, but that doesn’t mean that the word and the social phenomenon are fundamentally the same thing.

False analogies

I love a good analogy, as they can help to show parallels between different things. However, just because scenario A and scenario B have similarities with respect to characteristic X, that doesn’t mean that they share characteristic Y.

False analogies present scenario B as being like scenario A, when they actually have nothing to do with each other. An example of this is Hoyle’s fallacy, also known as the junkyard tornado fallacy. In his book The Intelligent Universe, astronomer Fred Hoyle wrote: “The chance that higher life forms might have emerged in this way is comparable to the chance that a tornado sweeping through a junkyard might assemble a Boeing 747 from the materials therein.” The “in this way” bit referred to abiogenesis, the biological concept that life can arise naturally from non-living material (Hoyle was a proponent of panspermia, a fringe theory I’d never heard of before, but gotta love that word). Even if abiogenesis is not a real thing, logically, this particular argument is nonsense.

False dichotomy

False dichotomies involve presenting something as being either one way or another, when in reality, there are multiple other options.

For example, let’s say that I was to argue that mental illness is not all biological, therefore it must be all environmental. That’s a false dichotomy, as there’s all kinds of middle ground between that either/or that’s getting left out.

Hasty generalizations

This fallacy involves making generalizations about a group based on a small or non-representative sample.

For example, if I knew two people who had COVID and had very mild symptoms, I would be making a hasty generalization if I were to argue that this meant that everyone who gets COVID only has mild symptoms.

Moral equivalence

The moral equivalence fallacy involves putting minor actions on a moral par with major atrocities. The argument that mask mandates during the COVID pandemic are abhorrent because they’re the moral equivalent of the Nazis forcing Jews to wear badges with the Star of David is an example of this. Even if you disagree with mask mandates, those are two very different things.

No true Scotsman

This is the argument that no one who is truly X would do action Y, therefore someone who has done action Y can’t be X. It then becomes unfalsifiable.

If no true Scotsman would wear undies under his kilt, and anyone who wears undies under his kilt is automatically not truly a Scotsman, then it’s impossible to establish the existence of a Scotsman who does wear undies & kilt.

Non sequitur

Non sequitur means does not follow. This involves making a leap to something not supported by previous statements, with a few steps missing along the way. This is like saying A=B and B=C, therefore A=D. Huh? Where the heck did D come from?

Post hoc (false cause)

Post hoc is short for the Latin phrase “post hoc, ergo propter hoc,” which means “after this, therefore because of this.” This logical fallacy involves assuming that because B happened after A, then B must have happened because of A (that’s where the “false cause” part comes in).

The sun rose this morning. I received an email five minutes later, but the sun did not in any way cause whoever it was to send me that email at that time.

Red herring

Red herring arguments involve going off on a tangent that distracts from the actual issue. Politicians use red herrings all the time.

When you tell someone that you’re feeling depressed, and they tell you that there are starving children in Africa, so you shouldn’t be depressed, that’s a red herring. Yes, there are starving children in Africa, but that’s just a distraction that’s not relevant to you being depressed.

Slippery slope

This involves making a chain of conclusions (A will cause B, then B will cause C, then C will cause D, through to Y causing Z) and suggesting that performing A will inevitably lead to Z. Just because a slippery slope exists doesn’t necessarily mean that people will always end up at the bottom of it. And if there are weaknesses in the chain of conclusions, the supposed endpoint Z may have nothing at all to do with first step A.

It’s not identifying that A could lead to Z that’s a fallacy; it’s assuming that A will inevitably lead to Z, and therefore one must never do A if one wants to prevent Z.

Straw man

The straw man fallacy involves misrepresenting an opponent’s position to try to make one’s own position look stronger. Meanwhile, strong arguments that an opponent would more likely to make are not addressed.

This is one of the logical fallacies that comens up a lot in politics. I tend to notice this more in the right-wing American media, not because they necessarily do it more, but because it’s easier for me to recognize that the “leftist” arguments that they’re countering are not actually arguments that anyone is making. For example, in 2021, hosts on the American network Fox News were repeating the idea circulating on social media that Joe Biden’s climate change plan would mean that everyone would have to cut their red meat intake by 90%.

Regardless of the merits or lack thereof in the climate change plan, Biden wasn’t actually saying people would need to stop eating red meat (source: Politifact). Red meat was the straw man that commentators were choosing to use to shoot down the plan rather than addressing what Biden was actually proposing.

I also notice this in creationist arguments. Again, this isn’t because only creationists do this, but because I’m more likely to recognize that they’re trying to refute arguments that no one is actually making. For example, some creationists will suggest that people who believe in the theory of evolution are arguing that humans evolved from birds, dinosaurs, fish, or what have you. Evolution suggests no such thing (this article addresses that misconception), and challenging an argument that your opponents aren’t actually making doesn’t do anything to support your position.


I’m a proud geek and love this kind of thing. Are there any of these logical fallacies that you tend to notice people making a lot?

Sources

The Psychology Corner: Insights into psychology and psychological tests

The Psychology Corner has an overview of terms covered in the What Is… series, along with a collection of scientifically validated psychological tests.

26 thoughts on “What Is… a Logical Fallacy”

  1. Thanks again for the post. Here is what hit me most “Argumentum ad populum (appeal to the people) is the argument that other people think so, therefore it must be true.” It feels like this is a description of the snowball effect for stigma against mental health progress. There is a critical mass that believes people with mental illness are dangerous or not to be trusted. This belief is magnified by the fact that so many people have this belief so others must also find it to be true. Is this a proper depiction of the term?

    1. I think that extends into the idea of socialization, where we learn about the world from the people around us. If we grow up regularly being exposed to other people’s negative ideas about certain groups, like mentally ill people, it’s hard not to absorb that, whether consciously or unconsciously.

  2. Twitter is a logical fallacy goldmine. I fall into ad hominem too often, feeling entitled because I consider the people I’m insulting to be horrid. I usually end up going back and deleting what I said.

    What wasn’t there is perhaps not a logical fallacy per se, but something I’ve noticed often afflicts me and others: I call it the “smartest person in the room” fallacy. I think it grows out of arrogance, so probably not in this category, but the end result of being wrong fits 😏

      1. It makes me uglier and I don’t even notice it happening. Imma try and stick to words, even as the thrill of hurling insults at politicians beckons 😉

  3. I love this post! Have never heard of tu quoque and some of the others. Saved this post for learning.

    A thought experiment: is there a fallacy that describes over reliance on another fallacy. Eg, a flat-earther may reference to the ad populism fallacy in their argument – “just because everyone says the earth is round does not make it so”. Would that be equivalent to a post hoc fallacy? Or ONLY if they follow with, “…therefore, the earth is flat.”?

    This is so fun!

  4. Great post. The logical fallacy I notice a lot lately is moral equivalence. (Not that I knew the term until reading this post 🙂 How anyone can think that asking people to be vaccinated in any way equates forcing people to wear Stars of David is beyond me.

  5. I also find “moral equivalence” a lot these days, as someone mentioned above. I’m getting a little tired of hearing store owners enforcing mask mandates referred to as “Gestapo,” when the Gestapo were killing thousands of people a day and largely responsible for the murders of six million Jews and five million non-Jewish people in Nazi Germany. This is in no way morally equivalent to asking a customer to please wear a mask.

    On the “appeal to nature” I have heard a lot of people allude to this in defending the legalization of marijuana as opposed to drugs that are “chemically synthesized in laboratories.” I doubt that appeal was of much help to Socrates as he drank the poison hemlock. Not to mention, if people loved marijuana so much because it’s “natural,” electronic vape devices wouldn’t be as popular as they are.

    Great to see all of these on one page. I’m going to have to bookmark it!

      1. I think part of this stems from lack of awareness as to who the “Gestapo” actually were. Not to mention, Marjorie Greene recently used the non-word “Gespacho” when she meant “Gestapo” which further validates the lack of awareness.

        But I don’t think all of it stems from being uninformed. Some people actually relate things like mask mandates to intense governmental oppression. It’s also interesting that the people calling “Gestapo!” invariably lean to the Right, as did Hitler’s Gestapo, and that they think of the people oppressing them as coming from the Left. Now that I recall, I wrote a column about this (I think you read it). It’s a perfect smokescreen for a Fascist agenda to call “Fascism” on somebody else.

        1. I heard that about Marjorie Greene – that was pretty funny. And that’s a very good point about it being Right-leaning people who are calling Gestapo, all while they’re leaning hard into book-banning.

          1. Exactly. On a related note, it’s beginning to bug me that I named my protagonist Winston Greene’s mother “Marjorie” in EDEN IN BABYLON, though of course when that came about around 2012 or so, this new Marjorie Greene was an unknown. I had been thinking about Marjorie Greene who was President of the American Philosophical Association back in the 70’s.

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