ELI5: All the common "logical fallacies" that you see people referring to on Reddit.

https://www.reddit.com/r/explainlikeimfive/comments/npkc7/eli5_all_the_common_logical_fallacies_that_you/

created by [deleted] on 24/12/2011 at 22:49 UTC

1139 upvotes, 84 top-level comments (showing 25)

Red Herring, Straw man, ad hominem, etc. Basically, all the common ones.

Comments

Comment by Atersed at 24/12/2011 at 23:43 UTC*

1525 upvotes, 88 direct replies

There are loads. But some common ones:

**Ad hominem** To attack the person not the argument: "We should increase taxes", "Don't listen to him, he only showers once a week".

I've been getting a lot of replies about this one. An ad hominem only occurs if you ignore the argument and attack the person to undermine the argument. "It's hot outside, let's all go for ice-cream." "That's a bad idea. I'm diabetic, you moron" is not ad hominem. It's not a very nice response, but he still counters the argument with a reason. "Men are more likely to drink-drive, so all men should be banned from driving." "You're a massive idiot." still isn't really ad hominem; he is attacking the person, but it is more like an insult than a counter argument. "Board games are the root of all evil. If we ban them then crime will go down." "You are clearly uneducated and a fool, so this cannot be true." is an ad hominem fallacy. And now I've probably made everything more confusing.*

**Circular Reasoning** Where the reason relies on the conclusion being true. "God exists because the Bible says so; Bible is true since it's the word of God".

**Slippery slope** The assumption that accepting one thing will lead to increasing undesirable other things. "If we let the immigrants in then they will take our jobs, leaving us homeless and then our children will be forced to work as prostitutes for food. Is that what you want? Child prostitutes?"

**False Dilemma** Forcing or suggesting there are only two possible options in a situation, where really there are many. "Steve insulted my mother, so I had to either punch him or be forever known as a wuss"

**Tu quoque** Literally *you too* (I think). Basically saying that if you don't do it, why should I? "My doctor told me to lose weight, but what does he know? He's fatter than me!"

**Appeal to Authority** Where a statement by an irrelevant authoritative figure or group is used. ~~"Dr Steve says the vaccine causes cancer, so that vaccine must be banned."~~ "Tiger Woods says this 10 bladed razor is way better than a 3 bladed one. The 7 extra blades therefore clearly make a difference."

**Appeal to Popularity** Where if a sizeable group of people belief in something, the belief must be correct. "300,000 Indians eat rice every day, therefore it must be healthy."

**Appeal to Ignorance** Where you assume something is true because it hasn't been proven false. Your standard "I don't know, therefore aliens".

**Loaded Question** Asking a question that presumes a certain fact. "What's your opinion on the immigrants that are ruining our society?" assumes immigrants are ruining our society, and by answering it directly you agree with this statement.

**Straw Man** Misrepresent the argument to make it easier to knock down. "We should give free fruit to school kids", "Yeah, let's just give everyone free food. That would just lead to obesity and a greater deficit".

**Post Hoc (ergo propter hoc)** Claiming that because something happens after something else, the first caused the second. "I wore my green socks today, and then found out my wife was leaving me. I didn't know she hated them that badly."

**Gamblers' Fallacy** Believing that a deviation in a series of (independent) chance events will soon be met by a deviation the opposite way. "I've given birth to six boys. My next kid is definitely a girl!"

**Middle Ground** Saying that a compromise between two extreme position is the correct one, solely because it is in the middle. "Schools are being forced to teach both creationism and the theory of evolution. The truth must be somewhere in between; they should teach the theory of creatioevolutionism."

**Appeal to Emotion** Relying on manipulating emotions rather than a solid argument. "Look at this poor little dog. Look at it! He looks so miserable and depressed. We should take him home and look after him." or "Meth. Not even once.[1]"

1: http://i.imgur.com/vmfng.jpg

**"Fallacy" Fallacy** The fallacy you might use after reading this list. An argument contains a fallacy, therefore the conclusion is wrong. "The *Meth. Not even once.* campaign is just one massive appeal to emotion fallacy. Therefore there is no reason to stop doing meth."

I've probably forgotten a few.

Examples are meant to be exaggerated. In real life they are often more subtle, and the names aren't important as long as you recognise that there's something wrong.

Edit: Adding more fallacies that others have mentioned for a more complete list.

Edit: Added *Middle Ground*, fixed some grammar errors, formatting.

Comment by fubo at 25/12/2011 at 04:08 UTC*

93 upvotes, 4 direct replies

Most of the kinds of fallacies you'll hear about here are **informal fallacies.** An informal fallacy means that an argument sounds kind of like it should be okay, but the conclusion doesn't follow from the premises.

For instance, take **ad hominem:** "Hitler says that dogs are nice; but Hitler is an evil man; therefore dogs are not nice." If we were really naïve, we would believe that *everything* that an evil man thinks is wrong. But we're not that naïve. Just because a horrible person believes a statement doesn't mean that statement is wrong! Horrible people like to breathe air and eat food, too; not everything they say or do is counter to the truth believed by not-horrible people.

There are also **formal fallacies,** although these are more rare. A formal fallacy is something wrong with the structure of the argument; the premises don't actually connect up to each other.

For instance, there is **affirming the consequent:** "All Al-Qaeda members are Muslims; Ahmed is a Muslim; therefore Ahmed is an Al-Qaeda member." Formal fallacies are usually really easy to spot, because something is backwards or disconnected. But people do sometimes make them, when they are unclear on how different groups or categories relate to each other.

There are other fallacies, too. For instance, there are **probability fallacies,** sometimes called **fallacies of evidence.**

Suppose that someone has been murdered, and the DNA evidence shows that the murderer has blood type A. The detective says, "Aha! Jane has blood type A, so we should investigate Jane!" The video evidence shows the murderer wore a green coat; and when the detective looks in Jane's closet, sure enough, Jane owns a green coat. So the detective accuses Jane of committing the murder.

Is Jane the murderer? Probably not! A lot of people have blood type A, and a lot of people own green coats. The detective has committed the **prosecutor's fallacy[1].** There wasn't any reason given to single out Jane in the first place! There's lots of people with blood type A and green coats, after all. That's not enough evidence to single out one person! Before the detective goes investigating Jane's closet specifically, the detective should have evidence that specifically makes Jane a suspect. This fallacy is sometimes also called **privileging the hypothesis** — picking out one of many different possibilities that fit the data, and treating it as the only one worthy of further investigation.

1: http://en.wikipedia.org/wiki/Prosecutor%27s_fallacy

Another probability fallacy is called the **base rate fallacy.** Suppose you have a new scanner at the airport that detects terrorists. The scanner is 99% accurate; it's only wrong 1% of the time. When Sam goes through the scanner, alarms go off — the scanner says Sam is a terrorist! What's the chance that Sam really is a terrorist? The fallacy answer is that we can be 99% certain that Sam is a terrorist. But that's not right!

Suppose there are a million people who go through the airport, and 100 of them are terrorists. The scanner is 99% accurate, so it will miss one of the terrorists and catch 99 of them; that part is obvious. But what about the 999,900 non-terrorists? The scanner is 99% accurate ... which means that it will accuse 1% of those innocent people — or 9999 people! — of being terrorists. Out of a million people, the scanner goes off for 99 terrorists plus 9999 innocents, or a total of 10098 alarms.

So, given that Sam set off the terrorist scanner, the chance is only 99 out of 10098, or just under 1%, that Sam is a terrorist. Even though the scanner is "99% right", *when it goes off* it's only 1% right, because terrorists are so rare — the *base rate* of terrorism is very low. The scanner catches 99% of all actual terrorists; but only 1% of the people it catches are actually terrorists.

The base rate fallacy is like a probability version of affirming the consequent. Just because the scanner detects almost all terrorists, doesn't mean that almost everyone the scanner detects is a terrorist.

Comment by JoeBourgeois at 25/12/2011 at 11:24 UTC

12 upvotes, 4 direct replies

University rhetoric teacher here. Rather than memorize a long list of fallacies (which don't cover a large number of fallacious arguments anyway), it's much better to learn to unpack the logical warrants in an argument using Toulmin's[1] system of logic[2].

1: http://www.kimburleymurphy.com/Notes/Literature/toulmin_logic.htm

2: http://owlet.letu.edu/contenthtml/research/toulmin.html

Comment by [deleted] at 24/12/2011 at 23:17 UTC*

79 upvotes, 6 direct replies

[removed]

Comment by Jack-is at 25/12/2011 at 02:30 UTC

12 upvotes, 4 direct replies

The *ad hominem* fallacy is a very commonly cited one, so you must take care not to misidentify it. One common mistake has been made in this very thread:

http://www.reddit.com/r/explainlikeimfive/comments/npkc7/eli5_all_the_common_logical_fallacies_that_you/c3ayl4t

While it may have been rude of a realreactionary to call Reddit liberals dumbasses, that remark was not used as a premise in his argument, and is therefore not an *argumentum ad hominem.* If he had said, "Reddit liberals are dumbasses, so their idea that there's a fixed amount of wealth in the world is wrong," that would be an *ad hominem* fallacy.

It's important to remember that rudeness and name-calling are not, in and of themselves, always indicative of an *ad hominem* fallacy. I've seen quite a few lively debates ended because someone got a bit rude and the opposition took it as an excuse to stop, even though there were perfectly sound arguments right beside the superfluous rudeness.

http://plover.net/~bonds/adhominem.html

Comment by GrammarAnneFrank at 25/12/2011 at 07:08 UTC

10 upvotes, 1 direct replies

There's one really really **really** important distinction that needs to be made about **ad hominem**, because i see this used incorrectly all the time. An ad hominem follows the form "Jane is a shitty person, therefore Jane is wrong." That is, you are arguing that an argument is wrong due to some characteristic of the person making the argument. If Jane were to make an argument, and I said "Jane is a shitty person," that's not necessarily an ad hominem. It's just good old fashioned abuse. In this second example, I haven't actually addressed the argument at all. Further, I could say "Jane is a shitty person, and here's why she's wrong." That's still not an ad hominem, since I haven't said that Jane being a shitty person means her argument is wrong.

Comment by [deleted] at 25/12/2011 at 03:10 UTC

7 upvotes, 1 direct replies

Top 20 Logical Fallacies (by the skeptics guide) http://www.theskepticsguide.org/resources/logicalfallacies.aspx

Comment by BrickSalad at 25/12/2011 at 05:26 UTC

9 upvotes, 0 direct replies

*Strawman** To construct a weak imitation of your opponent's arguments that is easy to defeat. This is unique among the fallacies in that it is impossible *not* to commit to some minor degree unless you perfectly understand your opponent's arguments. An example of a strawman is if you responded "how snooty of you to suggest that everyone tries to fool each other with strawmen!"

*Red Herring** In a detective novel, a Red Herring is a clue that doesn't help you out but instead leads you down the wrong path. In other words, it's a distraction. So, for example, let's say we're having a debate about the health of school lunches (I think they're unhealthy, you do not) and you argue that what we really need is more physical education. Yes, more physical education will help with the health of our students, but that doesn't make the school lunches any more or less healthy.

These are probably the two most common ones you will see people using on Reddit.

Comment by tadrinth at 25/12/2011 at 01:39 UTC

4 upvotes, 1 direct replies

I'm not sure it's one of the common ones, but Argument from Fictional Evidence always drives me nuts.

Comment by [deleted] at 25/12/2011 at 03:10 UTC*

4 upvotes, 0 direct replies

This PDF[1] is the specification for Critical Thinking A level. Scroll down to page 17 (section 3.1.11a) and it lists a dozen or so of the most common fallacies with explanation as to why they are fallacies and examples.

1: http://store.aqa.org.uk/qual/gce/pdf/AQA-2770-W-SP-10.PDF

Or if you want to lose a whole evening, then there's the obligatory Wikipedia List of Fallacies.

Comment by GoGo-Gadget at 25/12/2011 at 04:55 UTC

3 upvotes, 1 direct replies

There is a cool story you can read that references many ones in a playful way. We read this for my 8th grade English class when we were learning the fallacies and I found it both amusing and helpful. Love is a Fallacy

Comment by mjbat7 at 26/12/2011 at 02:11 UTC

3 upvotes, 0 direct replies

I don't know the formal name of this fallacy, but I would call it a **pedagogical fallacy**, and it goes as follows:

Person 1: I've been counting cards at this table all night and there's a pretty high chance that I'll win in the next couple of hands.

Person 2: Probably not, that's the **Gamblers' Fallacy**

Person 1: Really? Damn, maybe I'm wrong...

In this example, Person 1 probably wasn't committing the **Gamblers' Fallacy**, but because Person 2 was able to reference a quasi familiar term or official sounding term, person 1 feels compelled to accept that the term has been applied correctly.

Comment by Ranestorm at 26/12/2011 at 02:19 UTC

3 upvotes, 0 direct replies

One of my favorites is the **Texas Sharpshooter Fallacy**, that is picking out entirely random bits of information and focusing solely on a similarity or two in order to prove a larger pattern.

The name comes from a story of a Texan who owned this big empty barn, and every day to blow off steam he would take his pistol and take some shots at the side of the barn in a random fashion. After a while the barn wall became full of holes and, by pure random chance, there were some places where there were more holes clustered more closely together than others. The Texan then goes back and paints targets around these random places, so it looks like he was actually a really good shot and there was some recognizable pattern to his shooting, when in reality he wasn't aiming for anything at all.

Comment by cinemagical414 at 26/12/2011 at 02:56 UTC

2 upvotes, 0 direct replies

I think this applies:

*Law of small numbers** - when random chance is mistaken for a statistically significant pattern due to too small a sample size

e.g.: Blaming a few seasons' worth of warmer weather on climate change. Saying a basketball player is "playing hot" after sinking several shots in a row. Continuing to play a slot machine because of winning a few consecutive times.

Comment by revcasy at 26/12/2011 at 03:27 UTC*

4 upvotes, 0 direct replies

*Fallacy of the Single Cause** is a fallacy of oversimplification. "Kids in poor neighborhoods don't do as well academically because the schools in poor neighborhoods are not as good. If we want kids in poor neighborhoods to do as well as other kids we should fix their schools."

It may be a fact that bad schools contribute to bad academic performance, but there are numerous additional causes (e.g. family instability, poor nutrition, absent parents, etc.). So, in this example fixing the schools is not going to completely fix the problem.

Comment by [deleted] at 26/12/2011 at 04:50 UTC

5 upvotes, 2 direct replies

**Argument from personal incredulity** The argument that's one's personal inability to accept or understand something means it can't be true. "I can't believe/understand that so it can't be true".

**Argument from personal credulity** The argument that because something sense to you, it must be true. "Christianity just makes sense to me".

**Continuum fallacy (Fallacy of the beard, Fallacy of the heap, Line-drawing fallacy)** The argument that because no discrete line can drawn between two things, they are essentially the same thing. You see this a lot in abortion debates. For example "If a foetus isn't a person, tell me exactly when does a foetus becomes a person?"

Comment by Amarkov at 24/12/2011 at 23:16 UTC

12 upvotes, 2 direct replies

Assume you're arguing to me that we should increase taxes on paper.

Red herring is when someone brings up a distracting point to derail an argument. For instance, it would be a red herring for me to say "well okay but I don't think we should kill puppies".

A strawman is an opinion you claim that someone holds that they actually don't. If I told you "well unlike you, I don't think that 100% tax rates are a good idea", that would be a strawman.

Ad hominem is attacking the person you're talking to rather than their argument. It would be ad hominem if I told you "yeah well you're cheating on your wife so shut up".

Comment by voodoochild1997 at 25/12/2011 at 03:52 UTC

25 upvotes, 5 direct replies

*No True Scotsman** fallacy would be used in a situation such as:

Two Scottish men are eating oatmeal. One adds butter, the other adds syrup. The one that added butter tells the other, "No TRUE Scotsman puts syrup in his oatmeal!"

Essentially, if you identify with a group, everyone in that group is exactly like you (even if they're not).

Christians use this when justifying things like a child dying because their parents opted for prayer instead of surgery and another Christian says "No TRUE Christian would have done that."

Comment by driscoll at 25/12/2011 at 05:58 UTC

3 upvotes, 0 direct replies

Thanks for this ELI5. I learned most of this in Comp I last spring but forgot nearly all of it.

Comment by [deleted] at 25/12/2011 at 07:46 UTC

3 upvotes, 0 direct replies

I often see the perfect solution fallacy, which is a form of the false dilemma.

"People will always die in fires, so why have any firemen at all?"

The implication is that all imperfect states are equally desirable. Really, if we cannot live in a world where no one dies from fires, we want the rate of deaths per year to be close to zero.

Comment by phixion at 25/12/2011 at 14:49 UTC

3 upvotes, 0 direct replies

One I run into all the time is the **Hypothesis contrary to fact** fallacy. That's where someone says something like "If Case-A would have happened then Case-B would surely happen." Basically accepting a hypothetical as true. I hear arguments like this all the time when discussing history with people.

Comment by [deleted] at 26/12/2011 at 01:36 UTC

3 upvotes, 0 direct replies

Is there enough interest here to make a sub reddit about Fallacies?

Leadership of all sorts have learned how to use fallacies as a weapon to scramble public debate.

One way to start holding leadership accountable is to identify when they are deliberately using fallacies in their public statements.

Comment by LeonardoFibonacci at 26/12/2011 at 03:02 UTC

3 upvotes, 0 direct replies

Also, people posting in this thread may want to be careful of the Fallacy Fallacy-- that is, just because someone's argument is fallacious, it doesn't NECESSARILY mean they're wrong.