Logical Fallacies 101

School is supposed to teach us to think critically. Sadly, I think it usually misses the mark. I often hear people, who are probably quite bright and well-educated, make logical fallacies. Logical fallacies are flaws in reasoning. The problem is that on the surface, they seem to make sense! It’s only when you stop and think about it a bit more that you realize it’s a logical fallacy. I’ll give these people I hear the benefit of the doubt – they probably haven’t learned about logical fallacies before. It’s easier to recognize yourself or someone else committing a logical fallacy if you are at least aware of their existence. I’m not perfect and I probably still make these logical fallacies from time to time, but alas, awareness is the first step!

Consider this blog post a guide to the Logical Fallacies 101 course you never got in school. I really like the descriptions and (FREE) poster on this website: https://yourlogicalfallacyis.com/. I love it so much that I printed and laminated the poster and it is now sitting in my living room ;). I will be using their descriptions and general examples of common logical fallacies and then I will also offer a physiotherapy-specific example. I’d like to give PT-specific examples because it seems like people can understand it from an everyday point of view (e.g. correlation doesn’t equal causation – eating ice cream doesn’t cause people to wear t-shirts and shorts) but then completely forget about that in their PT world (e.g. person got better after treatment, therefore treatment must have caused person to get better).

thou-shalt not commit logical fallacies2

Many thanks to Praneeth Ellanti who helped me think of some PT-specific examples when I got stuck :). Check out his blog here: http://physiotheory.com/

Logical Fallacy
Description
General Example
PT-specific Example
Strawman
Misrepresenting someone’s argument to make it easier to attack.
By exaggerating, misrepresenting, or just completely fabricating someone’s argument, it’s much easier to present your own position as being reasonable, but this kind of dishonesty serves to undermine rational debate.
After Will said that we should put more money into health and education, Warren responded by saying that he was surprised that Will hates our country so much that he wants to leave it defenceless by cutting military spending.
Will says that the effects of manual therapy are probably more related to neurophysiological changes rather than changes in how a joint glides. Warren responds by saying that he is surprised that Will thinks manual therapy is useless.
Slippery Slope
Asserting that if we allow A to happen, then Z will consequently happen too, therefore A should not happen.
The problem with this reasoning is that it avoids engaging with the issue at hand, and instead shifts attention to adeline extreme hypotheticals. The merits of the original argument are then tainted by unsubstantiated conjecture.
Colin Closet asserts that if we allow same-sex couples to marry, then the next thing we know we’ll be allowing people to marry their parents, their cars and even monkeys.
Colin asserts that if the foot is overpronated, that will lead to excessive internal rotation of the tibia, causing internal rotation of the femur, which will cause the hip to drop, causing the contralateral shoulder to drop due to pulling on the posterior oblique sling, which finally will cause shoulder pain. (see this picture for example)
Special Pleading
Moving the goalposts or making up exceptions when a claim is shown to be false.
Humans are funny creatures and have a foolish aversion to being wrong. Rather than appreciate the benefits of being able to change one’s mind through better understanding, many will invent ways to cling to old beliefs.
Edward Johns claimed to be psychic, but when his ‘abilities’ were tested under proper scientific conditions, they magically disappeared. Edward explained this saying that one had to have faith in his abilities for them to work.
Edward Johns claimed to be able to move cerebrospinal fluid by mobilizing the bones of the skull. When the validity and biological plausibility of these claims were tested under proper scientific conditions, these claims were disproven. Edward explained that science has not advanced enough to be able to detect what he can feel.
Black-or-white
Where two alternative states are presented as the only possibilities, when in fact more possibilities exist.
Also known as the false dilemma, this insidious tactic has the appearance of forming a logical argument, but under close scrutiny it becomes evident that there are more possibilities than the either/or choice that is presented.
Whilst rallying support for his plan to fundamentally undermine citizens’ rights, the Supreme Leader told the people they were other on his side, or on the side of the enemy.
This person has an acute injury so they should be treated from a biomechanics perspective rather than a pain science perspective.
False Cause
Presuming that a real or perceived relationship between things means that one is the cause of the other.
Many people confuse correlation (things happening together or in sequence) for causation (that one thing actually causes the other to happen). Sometimes correlation is coincidental, or it may be attributable to a common cause.
Pointing to a fancy chart, Roger shows how temperatures have been rising over the past few centuries, whilst at the same time the number of pirates have been decreasing; thus pirates cool the world and global warming is a hoax.
Roger says that his patient felt better after a few treatment sessions with him so the treatment must have caused the patient to feel better.

(What other causes might there have been, even outside of non-specific effects? Think natural history, regression to the mean, clinician and patient bias)
Ad Hominem
Attacking your opponent’s character or personal traits in an attempt to undermine their argument.
Ad hominem attacks can take the form of overtly attacking somebody, or casting doubt on their character. The result of an ad him attack can be to undermine someone without actually engaging with the substance of their argument.
After Sally presents an eloquent and compelling case for a more equitable taxation system, Sam asks the audience whether we should believe anything from a woman who isn’t married, was once arrested, and smells a bit weird.
After Sally presents an eloquent and compelling case for alternative mechanisms of exercise in reducing pain, Sam asks the audience whether we should believe anything from a woman who doesn’t have her FCAMPT.
Bandwagon
Appealing to popularity or the fact that many people do something as an attempted form of validation.
The flaw in this argument is that the popularity of an idea has absolutely no bearing on its validity. If it did, then the Earth would have made itself flat for most of history to accommodate this popular belief.
Shamus pointed a drunken finger at Sean and asked him to explain how so many people could believe in leprechauns if they’re only a silly old superstition. Sean, however, had had a few too many Guinness himself and fell off his chair.
Shamus asked Sean to explain how he can think that there’s no such thing as good/ideal posture if so many other clinicians believe that there is.
Begging the Question
A circular argument in which the conclusion is included in the premise.
This logically incoherent argument often arises in situations where people have an assumption that is very ingrained, and therefore taken in their minds as a given. Circular reasoning is bad mostly because it’s not very good.
The word of Zorbo the Great is flawless and perfect. We know this because it says so in The Great and Infallible Book of Zorbo’s Best and Most Truest Things that are Definitely True and Should Not Ever Be Questioned.
I broke down the scar tissue/fascia/adhesions using my soft tissue techniques and they felt better after so the scar tissue/fascia/adhesions must have been causing the problem.
Appeal to Authority
Saying that because an authority thinks something, it must therefore be true.
It’s important to note that this fallacy should not be used to dismiss the claims or experts, or scientific consensus. Appeals to authority are not valid arguments, but nor is it reasonable to disregard the claims of experts who have a demonstrated depth of knowledge unless one has a similar level of understanding
Not able to defend his position that evolution ‘isn’t true’ Bob says that he knows a scientist who also questions evolution (an presumably isn’t herself a primate).
Not able to defend his position that shortened hip flexors cause gluteal inhibition, Bob says that it’s what his professors at school told him.
Appeal to nature
Making the argument that because something is ‘natural’ it is therefore valid, justified, inevitable, good, or ideal.
Many ‘natural’ things are also considered ‘good’, and this can bias our thinking; but naturalness itself doesn’t make something good or bad. For instance murder could be seen as very natural, that doesn’t mean it’s justifiable.
The medicine man rolled into town on his bandwagon offering various natural remedies, such as very special plain water. He said that it was only natural that people should be wary of ‘artificial’ medicines like antibiotics.
This ointment is made of natural ingredients only so it’s better than Voltaren.
Composition/division
Assuming that what’s true about one part of something has to be applied to all, or other, parts of it.
Often when something is true for the part it does also apply to the whole, but because this isn’t always the case it can’t be presumed to be true. We must show evidence for why a consistency will exist
Daniel was a precocious child and had a liking for logic. He reasoned that atoms are invisible, and that he was made of atoms and therefore invisible too. Unfortunately, despite his thinky skills, he lost the game of hide and go seek.
Spinal flexion under loading (especially when not trained), can lead to low back injuries. Therefore, spinal flexion is bad and should always be avoided.
Anecdotal
Using personal experience or an isolated example instead of a valid argument, especially to dismiss statistics.
It’s often much easier for people to believe someone’s testimony as opposed to understanding variation across a continuum. Scientific and statistical measures are almost always more accurate than individual perceptions and experiences.

Jason said that that was all cool and everything, but his grandfather smoked, like, 30 cigarettes a day and lived until 97 – so don’t believe everything you read about meta analyses of sound studies showing proven causal relationships.
Jason said that he knows he can reliably perform motion palpation and that joints do get stuck because he can feel it and make it change with his mobilizations/manipulations. Jason says to forget all the studies that show poor reliability (see this post for references) and poor validity (your SAL glide is probably more of a A glide if anything)
Appeal to Emotion
Manipulating an emotional response in place of a valid or compelling argument.
Appeals to emotion include appeals to fear, envy, hatred, pity, guilt, and more. Though a valid, and reasoned, argument may sometimes have an emotional aspect, one must be careful that emotion doesn’t obscure or replace reason.
Luke didn’t want to eat his sheep’s brains with chopped liver and brussel sprouts, but his father told him to think about the poor, starving children in a third world country who weren’t fortunate enough to have any food at all.
Luke warned his colleague not to hunch over while working on his laptop or else he may end up like the Hunchback of Notre Dame.
Tu Quoque
Avoiding having to engage with criticism by turning it back on the accuser – answering criticism with criticism.
Literally translating as ‘you too’, this fallacy is commonly employed as an effective red herring because it takes the heat off the accused having to defend themselves and shifts the focus back onto the accuser themselves
Nicole identified that Hannah had committed a logical fallacy, but instead of addressing the substance of her claim, Hannah accused Nicole of committing a fallacy earlier on in the conversation.
Nicole was talking about the potential dangers of repetitive lumbar flexion, quoting Stuart McGill’s work. Instead of addressing the repetitive flexion and low back concern, Hannah accused Nicole of appealing to authority.
Burden of Proof
Saying that the burden of proof lies not with the person making the claim, but with someone else to disprove.
The burden of proof lies with someone who is making a claim, and is not upon anyone else to disprove. The inability, or disinclination, to disprove a claim does not make it valid (however we must always go by the best available evidence).
Bertrand declares that a teapot is, at this very moment, in orbit around the Sun between the Earth and Mars, and that because no one can prove him wrong his claim is therefore a valid one.
Bertrand declares that he is manipulating his patient’s liver to fix his back pain, and that because no one can prove him wrong his claim is therefore a valid one.
The Texas Sharpshooter
Cherry-picking data clusters to suit an argument, or finding a pattern to fit a presumption.
This ‘false cause’ fallacy is coined after a marksman shooting at barns and then painting a bullseye target around the spot where the most bullet holes appear. Clusters naturally appear by chance, and don’t necessarily indicate causation.
The makes of Sugarette Candy Drinks point to research showing that of the five countries where Sugarette drinks sell the most units, three of them are in the top ten healthiest countries on Earth, therefore Sugarette drinks are healthy.
Picking all the acupuncture studies from the east (which are more likely to be positive and to be published) when rationalizing the use of acupuncture.
The Fallacy Fallacy
Presuming a claim to be necessarily wrong because a fallacy has been committed.
It is entirely possible to make a claim that is false yet argue with logical coherency for that claim, just as is possible to make a claim that is true and justify it with various fallacies and poor arguments.
Recognizing that Amanda had committed a fallacy in arguing that we should eat healthy food because a nutritionist said it was popular, Alyse said we should therefore eat bacon double cheeseburgers every day.
Recognizing that Amanda had committed a fallacy in arguing that we should do manual therapy because everyone in private practice does it, Alyse said we should therefore never do manual therapy.
Personal Incredulity
Saying that because one finds something difficult to understand, it’s therefore not true.
Subjects such as biological evolution via the process of natural selection require a good amount of understanding before one is able to properly grasp them; this fallacy is usually used in place of that understanding.
Kirk drew a picture of a fish and a human and with effusive disdain asked Richard if he really thought we were stupid enough to believe that a fish somehow turned into a human through just, like, random things happening over time
Richard suggested to Kirk to try eccentric hamstring strengthening exercises to reduce the tightness in his hamstrings. Kirk scoffed at the suggestion, asking Richard how contracting a muscle could make it feel any looser.
Genetic
Judging something good or bad on the basis of where it comes from, or from whom it comes from.
To appeal to prejudices surrounding something’s origin is another red herring fallacy. This fallacy has the same function as an ad hominem, but applies instead to perceptions surrounding something’s source or context.
Accused on the 6 o’clock news of corruption and taking bribes, the senator said that we should all be very wary of things we hear in the media, because we all know how very unreliable the media can be.
Alex said this journal article must be great since it is from a journal with a high impact factor.

(I think the point with this is that we should be critical of what we read, regardless of the source)
Middle Ground
Saying that a compromise, or middle point, between two extremes must be the truth.
Much of the time the truth does indeed lie between two extreme points, but this can bias our thinking; sometimes a thing is simply untrue and a compromise of it is also untrue. Half way between truth and a lie is still a lie.
Holly said that vaccinations caused autism in children, but her scientifically well-read friend Caleb said that this claim had been debunked and proven false. Their friend Alice offered a compromise that vaccinations cause some autism.
Holly said that poor timing of TA activation causes LBP in adults, but her scientifically well-read friend Caleb said that this cannot be true since studies have found improvements in LBP with TA training without corresponding improvements in TA activation timing (1). Their friend Alice offered a compromise that poor timing of TA activation causes LBP in some adults.

Phew, this was harder than I thought it would be! Can you think of any more logical fallacies? I’d love to hear about them. Feel free to call me out on it if you ever catch me making a logical fallacy ;).

References

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4 comments to this article

  1. PTStudent

    on April 9, 2016 at 5:34 pm - Reply

    I’ve really enjoyed reading your blog posts so far. This one in particular with the PT specific logical fallacies holds true in so many ways. I’m still in my 1st year of PT and it’s been an interesting ride so far…but I really want to learn how to better focus my thinking through a BPS lens, taking current principles of modern pain science into consideration. Would you suggest applying to be a PSD Mentee through the CPA? I’m kind of unsure as to how it would align with my role as a student because I’m still in the phase where I’m trying to learn all the information I can, not so much change my day-to-day thinking in clinical practice.

    • VeeWong

      on April 10, 2016 at 5:45 pm - Reply

      Thanks for checking out my blog – I’m glad you’ve been enjoying it so far! That’s great that you’re starting to think about this stuff now. I haven’t gone through the mentorship program yet (I’ve applied to be a mentee for this year) but I think that it’d be worth applying even if you’re a student. When I was a student, I had a couple of informal mentors and I found that really helpful when trying to understand how what I was learning in school fit in with the science behind pain (because let’s face it, sometimes there’s incongruence). I think a mentor can be helpful in providing guidance, or even an ear to listen, on how to integrate all the information you’re learning. What you get out of it as a student would be different from what you get out of it as a clinician but I think it’d be worthwhile either way. It might also be useful for when you’re on your clinical placements! That being said, I think they did say students are welcome to apply, though preference will be given to practicing PTs.

      Hope that’s helpful! Feel free to email me at veronica@veewong.com if you have any more questions :).

  2. Brian Cho

    on May 8, 2016 at 11:30 pm - Reply

    Hey Vee!

    I just wanted to say that this is a fantastic post! I’ll be sharing it as required reading to many of my colleagues :)!

    • VeeWong

      on May 9, 2016 at 8:51 am - Reply

      Thanks Brian! I’m glad you enjoyed it 🙂

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