Logical Fallacies

The Straw Man fallacy is, to my mind at least, one of the most underhanded forms of illogical argument that someone can use. It is also one of the most common logical fallacies you are likely to encounter and fairly easy to spot. The name of this fallacy is believed to come from a time when military training dummies tended to be constructed from straw. Whilst these dummies looked superficially like a real enemy, they were very easy to put down, straw not really being known for its ability to fight back. A straw man argument works in much the same way. The person setting up the straw man will describe a position that sounds superficially like their opponent’s actual position, but which is much easier to put down. They then attack this argument, rather than the position their opponent actually holds, and claim victory when they are able to defeat it. An example might go like this:

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Barry: I think that the laws related to marijuana should be relaxed.
Steve: But if we allow unrestricted access to drugs then there will be chaos.

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In this example Steve may well be right that unrestricted access to drugs would be a bad thing, however this is not the argument that Barry is making. Rather than addressing the actual issue at hand, whether the laws related to the specific drug marijuana should be relaxed, Steve has created a straw man argument about unrestricted access to all drugs that is far easier for him to argue against and much harder for Barry to defend.

If I have a favourite logical fallacy then it has to be this one, and no there is nothing weird about having a favourite logical fallacy. Post-hoc ergo propter hoc is Latin for “after this, therefore because of this” and is the idea that because event two happened after event one then event two must have been caused by event one. Those of you who, like me, have worked in any kind of service industry, and especially if you work in IT, will probably recognise this one. I long ago lost count of the number of calls that I got from people who used this form of invalid logic.

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“One of your IT guys came out and changed the toner in our printer and now my monitor isn’t working, what have they done to it?”

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“I never had a problem sending emails until our new temp started. I can’t help but think that they are causing the problem somehow.”

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Because event one, the IT guy coming out the change the printer toner, happened before event two, the guy’s monitor ceasing to work, he comes to the mistaken conclusion that these two events must be casually related, the first causing the second, when in fact they are entirely separate events.

An Ad hominem argument, or “an argument against the man “, is where you target a failing or flaw in the person making the argument and claim that this means that their argument is wrong as well, or alternatively that just because the person has some favourable trait that their argument is also favourable. Here is an example of how this might work:

“We should not accept Steve’s argument in support of allowing gay marriage, he has just got divorced himself.”

Unable to defeat the argument directly, in this case an argument in favour of gay marriage, the focus is shifted onto the person making the argument, specifically Steve’s recent divorce, or alternatively onto some person or group that can be loosely connected to it and criticizes them rather than the argument directly. The most common form of the Ad hominem argument is to simply insult the person making the argument and claim that this insult invalidates their argument. Claiming, for example, that a politician has bad BO and thus his plan for cleaning up the environment must be wrong or that just because someone doesn’t have a job their argument for the existence of Big Foot is wrong by default are ad hominem arguments. That said however it is important to note that while most examples of ad hominem arguments do include some kind of insult it does not follow that just because an argument includes an insult it automatically becomes ad hominem. For example:

“Your mother was a hamster and your father smelt of elderberries and thus your argument is wrong.”

That would be ad hominem because the whole argument is based upon the insult of the person. However, if you were to say something like:

“You empty headed animal food trough wiper; your argument is wrong because it does not fit the evidence.”

That is not ad hominem as, while it includes an insult, the insult is not the basis of the argument. So basically, you can insult someone all you like and still remain logically valid as long as you don’t use those insults as the basis of your argument, which is awesome. Another form of ad hominem argument plays on the idea of guilt by association. An example might go like this.

“Barry’s suggestion to increase the number of buses available to help ease traffic congestion is interesting. But do you know who else was in favour of mass transportation? Hitler.”

Here no attempt is made to address the actual points of Barry’s bus service argument, instead the whole thing is tarred and feathered by relating it to something with negative connotations, in this case Hitler and his use of mass transportation during World War 2.

This form of fallacy involves making a pre-emptive strike to discredit your opponent, and therefore their argument, by saying something that will produce a biased response in your audience. This is a form of ad hominem fallacy as it tends to be directed at the person as a way of making their arguments seem less valid or trustworthy.

“Before we look at the evidence, I would like to remind people that my opponent was once investigated on suspicion of having committed fraud.”

“My policy will provide the best options for our children, only someone who hates children would disagree with it.”

“And now former Playboy Playmate and famous nose picker Jenny McCarthy will talk to us about the dangers of vaccination.”

Before a single point is raised or piece of evidence presented the audience is already encouraged to disregard anything the fallacy maker’s opponent is likely to say due to some negative aspect of themselves or the group they represent. Another subtler, and less intentional, form of this fallacy that you will probably come across might go something like this:

“Oh, that is my favourite film, what did you think of it?”

By saying that it is their favourite film they have biased the person they are talking to into giving a positive, or at least less negative, response in order to not hurt their feelings. Your stated opinion of the film is therefore much more likely to be based on not wanting to upset your friend than on the merits of the movie itself.

These are technically two separate fallacies and yet they are similar enough and stem from the same core mistake to be listed as one. An argument from ignorance is where you claim that a premise is true because it has not been proven false or alternatively false because it has not been shown to be true. A common example of this in relation to science is to claim that a specific field of scientific investigation, such as big bang cosmology or abiogenesis, is false because scientists do not currently understand every aspect of it. Alternatively, a proponent of the paranormal may claim that ghosts are real due to the fact the science has not proven them false. This later example often also results in the proponent wrongly trying to shift the burden of proof onto the skeptic.

An argument from personal incredulity on the other hand is, as the name implies, a more personal claim that something is false, or true, because you personally can’t think of an alternative. An example of this fallacy is often employed by UFO proponents.

“It didn’t look like any airplane I’ve ever seen so it must have been an alien spaceship.”

“I’ve no idea what it was I saw, but clearly they were using some form of trans-dimensional technology.”

In both these cases the person is using their own lack of knowledge about what they have actually seen in order to reach their conclusion. Now it is important to remember that with this fallacy you are not saying that the person committing the fallacy is ignorant in an insulting way. You are not implying that they are a fool or uneducated, but rather that they are using their lack of knowledge about the subject as the basis of their argument. We are all ignorant about something, it is not an insult to have this pointed out, it is how we learn after all.

Special Pleading is a form of fallacious argument that involves someone claiming that something (be it God, ESP, ghosts etc) is exempt from a generally accepted rule or principle but without producing any evidence or logical reason as to why this should be the case. A very common example of this comes from proponents of pseudoscientific or paranormal claims who state that their claim is somehow beyond the ability of science to accurately test. This means that when these claims are tested, and the results come back overwhelmingly negative, they can turn round and still claim to be correct and that it was the inability of science to accurately test their claim that produced the negative result, rather than their claim simply being false. It may also be suggested that ESP, for example, does not work in the presence of skeptics, which is why all skeptical investigations into such claims come back negative. This is a perfect example of special pleading.

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It is also Ad-Hoc reasoning, which basically means making up a reason for something after the fact. This is something that happens a lot when testing pseudoscientific and paranormal claims. A practitioner might claim to get accurate results nine times out of ten and yet when tested perform no better than would be expected by chance. Rather than admit that maybe they don’t have special powers they will usually invent an ad-hoc reason for why it didn’t work this time. The spirits don’t like being tested, their power doesn’t work if people who don’t believe in it are nearby, they were not feeling very well at the time, they can’t use their power unless it is to directly help someone. Anything but admit the truth that their powers are non-existent.

A False Dichotomy is where you reduce all possible options down to just two and then state that if you can show one option to be wrong then the other must be correct by default. This fallacy is often used as a way of shifting the focus away from the fact that you don’t actually have any evidence to support your side of the argument by exposing apparent weaknesses in your opponent’s argument and claiming these as evidence in your favour. It is known as a false dichotomy or false dilemma because it is never demonstrated that the two options being presented are the only ones possible.

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Let’s say we have two suspects in a murder investigation, Adam and Bob. We look at the evidence and see that it is not possible for Adam to have committed the crime and therefore conclude that this means the killer must have been Bob. This would be a false dichotomy, showing that Adam is not the killer is not the same thing as showing that Bob is. There is also no reason to believe that this issue has to be a two-horse race, or that the exclusion of one option automatically makes the other one correct. Maybe the real killer is Charlie?

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This logically fallacy is also sometimes referred to as the fallacy of the excluded middle. This is worth mentioning mainly in order to avoid confusion with the Law of Excluded Middle that we looked at earlier in this article. The fallacy applies when you are only offered two options when more actually exist, whereas the law of excluded middle applies when there are legitimately only two options, for example true or false, and it is impossible for the middle or third option to exist.

This fallacy it pretty much the opposite of a false dichotomy. Rather than focusing on the two extremes to the exclusion of other options this fallacy assumes that the answer must lie in between the two options or in a combination of the two. While there are times when this may indeed be the case, sometimes the truth really does lie at one of the extremes. For example, if person A believes person X is pregnant and person B believes person X is not pregnant the truth cannot be somewhere in-between these two choices, it is either one or the other. Perhaps a more realistic and nuanced example might involve different political parties and their approach to taxes. Party A says that dropping taxes by 30% is the way to solve a problem while Party B suggests raising them by 10% is the best thing to do. To conclude that the best solution therefore would be to drop taxes by 10%, thus putting the new tax rate midway between the levels proposed by both parties, is a fallacy and likely to result in neither party being able to accomplish their goals.

This is a favourite of conspiracy theorists of all stripes and involves throwing out so many arguments that your opponent is simply unable to respond to them all.[1] They can then claim victory even if their opponent was able to destroy all of the arguments that they were able to get to in the time available. This works because it generally takes far longer to explain why a claim is incorrect than it does to simply state the claim in the first place. It also gives the impression that the person using this form of argument is very well versed in the topic at hand when in fact they could simply be repeating talking points without any real understanding to back them up.

“For those who believe that JFK was assassinated by Lee Harvey Oswald I have these questions. Why did people hear shots from the Grassy Knoll? Why did Kennedy’s head go “back and to the left” if he was shot from behind? How was Oswald able to pull off three shots in such a short amount of time? How do you explain the “loss” of the arrest records related to the three “tramps”? And how about the trajectory of the “Magic Bullet”, do you really expect us to believe a single bullet could account for all the injuries?”

All of these points have answers, and yet to address them all takes time, and most likely more time than is available in the average debate. Even if you are able to conclusively explain why Kennedy’s head would move “back and to the left”, as done highly effectively on the MythBusters TV show, the conspiracy theorist can still hang onto the fact that you didn’t have time to cover the “Magic Bullet” issue and claim victory.

[1] This argument is also often referred to as the Gish Gallop, after creationist Duane Gish who employed it on many occasions.

The red herring fallacy involves the use of an argument that distracts from the actual point at hand. In the previous fallacy the loss of the “tramps” arrest records is a good example of a red herring. Though this does sound suspicious and makes it seem like the truth behind JFK’s assassination may lie elsewhere it does nothing to address the actual facts supporting Lee Harvey Oswald as the sole gunman responsible. It is a distraction designed to get people thinking about something other than the evidence at hand. If 9/11 was really caused by Islamic terrorists, then why did President George W Bush continue reading to school children after being told that the second tower of the World Trade Center had been hit? I don’t know why he did this, I am sure he had his reasons, but this line of reasoning does nothing to argue against the evidence that Islamic terrorists were responsible for the attack, it is a red herring designed to cast doubt as to who was actually behind the atrocity. And on the subject of casting doubt I feel I would be remiss if I did not mention the great example of a red herring argument created by Trey Parker and Matt Stone for the “Chef Aid” episode of the TV series South Park in which attorney Johnnie Cochran unleash his infamous “Chewbacca defence”. Here Cochran’s character deliberately attempts to distract the jury from the facts of the case[1] with this interesting line of reasoning.

Cochran: Ladies and gentlemen of this supposed jury, Chef's attorney would certainly want you to believe that his client wrote "Stinky Britches" ten years ago. And they make a good case. Hell, I almost felt pity myself! But, ladies and gentlemen of this supposed jury, I have one final thing I want you to consider. Ladies and gentlemen, this is Chewbacca. Chewbacca is a Wookiee from the planet Kashyyyk. But Chewbacca lives on the planet Endor. Now think about it; that does not make sense!

Gerald Broflovski: Dammit!

Chef: What?

Gerald: He's using the Chewbacca Defence!

Cochran: Why would a Wookiee, an eight-foot tall Wookiee, want to live on Endor, with a bunch of two-foot tall Ewoks? That does not make sense! But more important, you have to ask yourself: What does this have to do with this case? Nothing. Ladies and gentlemen, it has nothing to do with this case! It does not make sense! Look at me. I'm a lawyer defending a major record company, and I'm talkin' about Chewbacca! Does that make sense? Ladies and gentlemen, I am not making any sense! None of this makes sense! And so, you have to remember, when you're in that jury room deliberatin' and conjugatin' the Emancipation Proclamation, does it make sense? No! Ladies and gentlemen of this supposed jury, it does not make sense! If Chewbacca lives on Endor, you must acquit! The defence rests.

By obscuring the argument with irrelevant information, the strength of the case’s real facts are effectively weakened.

[1] In case you have not seen the episode, the character Chef has an old recording that shows that he wrote the hit song “Stinky Britches” and approaches a “major record company” requesting that he be credited as the composer. The record company responds by suing Chef for harassment and hiring Jonnie Cochran to defend them.

A Tautology, or circular reasoning or begging the question[1], is where the conclusion of the argument is also the premise of the argument. There are two slightly different ways in which something can be a tautology. The first is a statement that basically says A=B therefore A=B, for example someone might say that acupuncture works because it affects the flow of Qi energy. As acupuncture is claimed to be a way to manipulate Qi energy what is actually being said here is “manipulating Qi energy works because it manipulates Qi energy”. The other form of tautology is probably a bit easier to both spot and understand. Here someone makes an argument in which their early statements are evidence for their later statements and their later statements are the evidence for their earlier ones. It might go something like this:

Steve: How do you know the Great Leader is telling the truth?

Barry: Because he speaks for the Ancient Spirits.

Steve: How do you know he speaks for the Ancient Spirits?

Barry: Because the Great Leader tells us he does.

Steve: But how do you know the Great Leader is telling the truth?

And thus, the discussion repeats itself. Interestingly there are legitimate uses for this line of reasoning as well as a number of well accepted scientific theories that are basically tautologies. For example, gravity. Why do things fall down? Because of gravity. How do we know there is gravity? Because things fall down.[2] That’s a tautology and yet it is a legitimate one. Let me see if I can lay that out in a slightly clearer fashion. If it can be shown that A proves B and that B proves C and that C proves D and that, finally, D proves A then we can legitimately state that A proves D and by extension B proves A. Because of this, you should always carefully examine the individual steps involved in any argument that you believe to be a tautology. If the individual steps are valid then it is possible that the argument as a whole may be valid even though it appears circular in nature.

[1] A pet peeve of mine is when someone uses the term “begs the question” to mean “raises the question”. That is not what begging the question means people.

[2] Yes, ok I know there is more to it than that, but the basic point stands.

The No True Scotsman fallacy is a different form of circular argument. An argument is made and when a counter argument is offered it is rejected as not being a “true” example of what is being discussed. The original example for this is still one of the best.

Angus: All Scotsmen are brave.

Donald: But what about Dougal? He is a coward.

Angus: Ah but Dougal isn’t a true Scotsman

Here Angus is basically making being brave part of the definition of being a Scotsman. As Dougal is not brave then he is not a true Scotsman. The definition of “Scotsman” that Angus is using is circular in that the conclusion, that Scotsmen are brave, is included in the premise, that you can only be a Scotsman if you are brave.

The Argument from Final Consequences is basically an illogical line of reasoning that states that if the end result of a premise is undesirable then the premise itself must be false. Alternatively, if the end result is positive then the premise must be true. One example of this that I have come across numerous times myself is the Hitler/Evolution argument.

“Hitler was simply following the rules of evolution, survival of the fittest, when he killed all those Jews. Evolution? More like Evilution.”

The argument here is that the theory of evolution is wrong because Hitler used it to develop his master race and as an excuse to kill all the people, he found undesirable, such as Jews, gypsies and homosexuals. Now even if this was true, and the evidence seems to indicate that it is not[1], it would not be evidence that the theory of evolution was incorrect. The atomic bomb dropped on Hiroshima was a result of Einstein’s work and caused approximately 70,000 immediate deaths and an estimated 200,000 additional deaths due to radiation exposure. However, this horrific body count doesn’t mean that the equation E=MC2 is incorrect.

[1] Hitler’s views appear to have been based more upon the discredited ideas of eugenics and the well-known concepts of animal breeding than upon natural selection. In fact, On the Origin of Species was one of the books banned in Nazi Germany.

This fallacy follows nicely from the Argument from Final Consequences in that it takes the actual end result of an argument or action and compares it to an ideal and often unrealistic alternative. For example, someone might argue against giving money to a homeless person as it does nothing to address the nation’s homeless problem as a whole. Alternatively, a politician’s plan to help 10,000 unemployed people find work might be dismissed as it is unable to find all unemployed people jobs. Small, incremental attempts at improvement are mocked as they fall far short of a perfect solution. The person arguing against your positions does not need to come up with a better solution, they just need to point out that your solution is not perfect and then claim victory.

The Argument from Authority revolves around the idea that if the person or group making the claim are considered to be authoritative then the claim, they are making must be true. This is fallacious since just because someone happens to be a figure of authority it doesn’t mean they can’t be wrong. If the truth of your statement is based only on the fact that it comes from an authority figure rather than any actual evidence or logic, then your argument is on very shaky ground. Anyone who watches or reads the news on a regular basis will probably have come across this logical fallacy many times. Whenever you come across the statement “scientists say” or “experts claim” or “doctors recommend” then you are witnessing an argument from authority. Now this doesn’t automatically mean that what the news report is saying is wrong, but if this appeal to authority is all the evidence presented in support of a claim then that is a good reason to be skeptical about it.

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As with some other fallacies however there are times when the argument from authority can be a legitimate starting point from which to judge the validity of a claim. If a subject, such as the idea that the global climate is changing in part due to human causes, is said to have achieved a consensus within the scientific community then this means that the vast majority of scientists agree that the theory is correct, such as in this case where something like 97% of climate scientists agree that climate change is partly caused by humans. As such, a claim of scientific consensus can be a good jumping off point in arguing for the validity of a scientific theory. However, it is important to remember that the truth of the claim must always eventually come down to the legitimacy of the evidence and the logical reasoning.

This is a fairly simple one to understand. Just because an idea is popular does not mean that it is right. Homeopathy is a multi-million-pound industry and is used by many thousands of people and sold in countless shops all over the country. Should we therefore conclude that it works just because it is popular? No, it’s just water people.[1] Another example might be that nine out of ten people voted for X, therefore X is the best thing for the country; but just because X is popular does not mean that it is the best thing to do. However once again it is possible for an argument from popularity to be logically valid, in this case when the topic at hand is, well, popularity. If 90% of the people in your group vote to go to the pub and so you decide that the group should go to the pub this is a perfectly logical conclusion, it is the one supported by the most people in the group. However, if you conclude that therefore going to the pub is the best possible thing you can do you are once more committing a fallacy.

[1] It is worth mentioning that Boots chemists, the UK’s biggest high street chemist, are on record as saying that they know homeopathy does not work and that they sell it because it is popular.

This term is Latin for “Doesn’t Follow” and is used to describe an argument in which the conclusion does not follow from the premises put forward for it. Here’s one you may have come across.

“The fires in the Twin Towers did not get hot enough to melt steel; therefore, they were brought down by explosives as part of a government conspiracy to get the USA involved in a war with Iraq.”

Here we have a statement, the fires in the Twin Towers were not hot enough to melt steel, and that is correct, they weren’t.[1] But the conclusion that it was therefore all a government conspiracy simply does not follow from this argument, thus the logic is invalid.

[1] And of course, they didn’t need to be, they only needed to be hot enough to weaken the steel to the point that they could no longer support the weight above them, and they were more than hot enough to do that.

A slippery slope argument states that because you accept a milder form of the argument or proposition then you must also accept an extreme form of it as well. Not only is this not the case but also in many cases accepting the milder argument cannot even be logically argued to lead to acceptance of the more extreme form. It is also a form of the non sequitur fallacy, in that the conclusion doesn’t really follow from the premise. Slippery slope arguments often pop up in highly charged political debates.

“If you support a woman’s right to choose then clearly you must also be in favour of murdering disabled children.”

“By voting in favour of health care reforms you are lending your support for the government to form death panels to decide who gets to live and who should die.”

Ok technically this is not a logical fallacy; however, it is something that as a card carrying skeptic you are more than likely to come across. Quote mining is the practice of taking a quote from someone who does not support your position and putting it forward as an argument in favour of said position. Personally, I think this is one of the most dishonest forms of argument that you will come across, though I will accept that it is equally likely to be done as a result of ignorance as it is of malicious intent, as many people just copy and paste these things from websites. As such I always prefer to educate rather than reprimand when I encounter something like this. One of the best and in my experience most commonly encountered examples of this comes from Charles Darwin’s On the Origin of Species. The often-quoted section states:

“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.”

This is used to support the idea that even Darwin himself did not fully accept the theory of evolution by natural selection as valid and in fact believed it to be absurd. This quote is indeed accurate, but what makes it an example of quote mining is that it is used to support an argument that the author is not making and does not agree with. In this case this is very easy to see as in the very next sentence this quote continues:

“Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.”

It is very easy to find things people have said that seem to support almost any position imaginable when taken out of context. As such whenever you come across a quote it always pays, where ever possible, to look it up and read it in its original setting to see what the author actually meant by their statement. One thing to keep an eye out for that might help you identify when someone is quote mining are references. If someone is quote mining then more often than not, they will not reference the source of the quote as this would make it too easy for someone to check out what was actually said for themselves, and this is the last thing they want. If you see a quote that states who allegedly said it but has no mention of where it is from, well, then it pays to be skeptical.