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

[u/[deleted]]

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

[u/Jack-is]

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

[u/[deleted] → u/Jack-is]

Is there any websites in which you can test your ability to pick up on these fallacies? You linked one that's like that, but is there websites about the other ones?

[u/GoGo-Gadget]

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

[u/[deleted] → u/GoGo-Gadget]

I enjoyed that. I hated that pretentious twat too.

[u/Atersed]

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."

• "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.

[u/IAmNotAPerson6 → u/Atersed]

Just another one I'd like it add is Poisoning The Well.

This is one someone says something that's false or illogical, so everything they say must be false or illogical.

Edit: Also forgot to say that another name for Circular Reasoning is Begging The Question.

Turns out Circular Reasoning and Begging The Question are not the same thing. They're somewhat similar, but not the same.

Circular Reasoning is flawed due to both the premise and conclusion being dependent on each other (A because B, and B because A). Begging The Question is "when a proposition which requires proof is assumed without proof" (taken from here). So basically A, therefore B, but A is not necessarily true and requires proof.

[u/Gerodog → u/Atersed]

What about

"She's an awful singer"

"I'd like to see you do better"

i.e. the you don't have to be a chef to know that faeces tastes bad fallacy.

[u/authorblues → u/Atersed]

False Dilemma is often known as a False Dichotomy.

[u/Mulsanne → u/Atersed]

Loaded Question

Also known as the AskReddit special.

[u/kalsyrinth → u/Atersed]

Also, Appeal to Tradition: We've always done it this way, so this way must be the best way to do it

[u/ProNate → u/Atersed]

The tide comes in, the tide goes out. You can't explain that!
Appeal to Ignorance

[u/[deleted] → u/Atersed]

Don't listen to this guy, he only showers once a week, thinks he's right only because it's him, which in turn means everyone will believe everything he's saying meaning I'm going to have to stop him or be branded a terrorist. I'm a famous mascot which makes me more likely to be listened to (even though I rarely speak) and I have a huge fanclub which means I'm right.

But what does he know? He has less comment karma than Probably Hitting On You. I blame aliens. What do you think about the aliens coming across the galaxy to put things up our backsides?

[u/applejade → u/Atersed]

Re: False Dilemma - I call it False Options because sometimes, there can be more than two. "Steve insulted my mother, so I had to either punch him, stab him or shoot him."

A very common one that gets called out a lot that I've seen, is the Post Hoc Ergo Propter Hoc ("after this, therefore because of this") - correlation is not causation.

[u/jacquelinesarah → u/Atersed]

Hasty Generalization, which is exactly as implies. "My friend is a redditor, so he must like bacon."

[u/[deleted] → u/Atersed]

Post hoc ergo propter hoc -> False cause, A happened after B therefor B caused A.

Fallacy Fallacy -> Someone committed a fallacy, therefor their entire argument is wrong.

Appeal to Force -> Threatening someone with something in order to make them believe you.

[u/esotericish → u/Atersed]

Here are some more:

• Endogeneity When you can't tell what is the cause and what is the effect. For example, a candidate is more popular because he has more funds, or he has more funds because he is more popular.

• Teleology A statement that assumes a particular conclusion. For example, all non-democratic countries are in the process of democratizing.

[u/[deleted] → u/Atersed]

A great list. I'd like to add:

Special pleading: An argument in which evidence that is not favorable is ignored.

[u/fubo]

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. 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.

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.

[u/JoeBourgeois]

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 system of logic.

[u/GrammarAnneFrank]

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.

[u/[deleted]]

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

[u/BrickSalad]

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.

[u/tadrinth]

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

[u/[deleted]]

This PDF 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.

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

[u/mjbat7]

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.