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Fallacies and BiasesFallacies and Biases

how NOT to think logically

George Matthews

2020

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How logical are we really?How logical are we really?

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We may all be capable of listening toreason but...


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We get fooled by fallacies.


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Fallacies are bad argumentsthat can look good if we arenot paying attention.


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Our thinking gets short-circuited by cognitive biases.


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Our thinking gets short-circuited by cognitive biases.

Cognitive biases are "bugs"in our mental operatingsystems that convince usthat we know what just isn'tso.


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Types of fallaciesTypes of fallacies

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Fallacies of relevanceFallacies of relevance

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Rely on irrelevant information to push the argument along.

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Fallacies of ambiguityFallacies of ambiguity

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Depend on multiple meanings of key terms to fool us.

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Fallacies of presumptionFallacies of presumption

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Rely on hidden assumptions to establish their conclusions.

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Rely on hidden assumptions to establish their conclusions.

NOTE: fallacies are typically invalid arguments that rely on tricks to close the gap betweenpremises and conclusions.

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Types of cognitive biasesTypes of cognitive biases

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Hot biasesHot biases

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Motivated irrationality: ways in which our thinking goes off the rails whenits results would con�ict with what we want.

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Cold biasesCold biases

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Unmotivated irrationality: mistakes in reasoning that are by-products ofthe way our minds are built.

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Unmotivated irrationality: mistakes in reasoning that are by-products ofthe way our minds are built.

NOTE: cognitive biases are the result of the complexity of our mental "software" and the factthat our reasoning minds are not entirely separate from our emotional and perceptual minds.

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fallacies offallacies ofrelevancerelevance

fallacies offallacies ofambiguityambiguity

fallacies offallacies ofpresumptionpresumption

hot biaseshot biases

cold biasescold biases

Jump to conclusions based on inadequateevidence.

Appeal to irrelevant details.

Rely on our tendency to see lots of connectionseven when they are not as strong as they seem.


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Stephanie is a scientist and she says that vaccinescause autism.

Thus vaccines are not as safe as the doctors aretelling us.

Appeal to authorityAppeal to authority

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Stephanie is a scientist and she says that vaccinescause autism.

Thus vaccines are not as safe as the doctors aretelling us.

While we often have no choice but to rely on experts,simply appealing to their expertise is never a good idea.Instead we should see what their claims are really based on,otherwise we still have no real reason to believe what theytell us.

Appeal to authorityAppeal to authority

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My trainer has me on a strict diet and says that myhealth will be better if I lose some weight.

But I saw him binge eating ice cream the other day,so I guess his advice is worthless.

Ad hominemAd hominem

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My trainer has me on a strict diet and says that myhealth will be better if I lose some weight.

But I saw him binge eating ice cream the other day,so I guess his advice is worthless.

Even if we might attack someone for not "praticing whatthey preach," that is really irrelevant in that the sameargument might have been uttered by someone else.

Ad hominemAd hominem

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Segregation laws were once popular in the Americansouth, they were democratically enacted.

Therefore segregation was acceptable.

Popular appealPopular appeal

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Segregation laws were once popular in the Americansouth, they were democratically enacted.

Therefore segregation was acceptable.

The majority of course might be wrong, no matter hownumerous they are. This is why democratic societies arenot only based on the principle that the majority gets todecide but instead we all have rights that protect us fromthe majority.

Popular appealPopular appeal

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Matthews, either I pass this class or you might endup having an unfortunate "accident."

Ha! I knew you would realize my work was betterthan you �rst said it was.

Appeal to forceAppeal to force

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Matthews, either I pass this class or you might endup having an unfortunate "accident."

Ha! I knew you would realize my work was betterthan you �rst said it was.

Threats might be effective as a way of getting people to dowhat you want, but they don't really provide us with anyreasons for belief.

Appeal to forceAppeal to force

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If evolution is correct then we are all related to allother organisms on the planet.

I refuse to admit that I am related to cockroaches inany way.

Therefore evolution must be wrong.

Appeal to consequencesAppeal to consequences

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If evolution is correct then we are all related to allother organisms on the planet.

I refuse to admit that I am related to cockroaches inany way.

Therefore evolution must be wrong.

While we may not like the consequences of a theory, if theevidence really supports it, we'll just have to get used tothem.

Appeal to consequencesAppeal to consequences

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Women should not be allowed into combat positionsin the military, since, after all, women are not asaggressive as men are.

Naturalistic fallacyNaturalistic fallacy

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Women should not be allowed into combat positionsin the military, since, after all, women are not asaggressive as men are.

There are a couple of problems with this argument, �rst notall men and women �t the general pattern. Second itignores the distinction between the way things are bynature and what we decide based on moral concepts likewho deserves and owes what.

Naturalistic fallacyNaturalistic fallacy

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This study was funded by a large pharmaceuticalcompany, so we can dismiss it as propagandaintended only to serve the interests of thecorporation's stockholders.

Genetic fallacyGenetic fallacy

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This study was funded by a large pharmaceuticalcompany, so we can dismiss it as propagandaintended only to serve the interests of thecorporation's stockholders.

This fallacy is a generalization of the last one -- it appeals tothe origins of something to determine the basic nature ofthat thing. Like other fallacies of relevance this argumentmistakes the messenger for the message -- isn't what is saiddecisive, not who says it?

Genetic fallacyGenetic fallacy

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Why do you keep saying that I am guilty ofcommitting a crime, when there are importantbusiness decisions that need to be made in runningthis company?

Red herringRed herring

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Why do you keep saying that I am guilty ofcommitting a crime, when there are importantbusiness decisions that need to be made in runningthis company?

This is less of a formal argument style and more of adebating tactic. Diverting attention from the topic at handdoesn't settle it one way or the other.

Red herringRed herring

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I oppose taxation because it involves taking moneyfrom me unwillingly and that is the same thing astheft!

Weak analogyWeak analogy

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I oppose taxation because it involves taking moneyfrom me unwillingly and that is the same thing astheft!

Analogies can help us illuminate obscure or abstractconcepts, but they can also mislead us since they only go sofar. We may wonder in this case about any relevantdifferences between taxation and theft.

Weak analogyWeak analogy

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Rely on shifting and playing around with themeanings of words.

Some terms are vague, and some have multipleand con�icting meanings.

Rely on our tendency to see lots of connectionseven when they are not as strong as they seem.


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Religion depends on faith in God.

Science depends on faith in observation and data-analysis.

Therefore science is not really very different fromreligious belief.

EquivocationEquivocation

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Religion depends on faith in God.

Science depends on faith in observation and data-analysis.

Therefore science is not really very different fromreligious belief.

This argument overlooks important differences betweenthe meaning of "faith" in these two contexts. Science isbased on public evidence, religion is not.

EquivocationEquivocation

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My opponent in this debate has stated that shedoesn't believe in the Biblical creation story.

But that amounts to saying that there is no meaningat all in life, which is ridiculous.

Straw personStraw person

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My opponent in this debate has stated that shedoesn't believe in the Biblical creation story.

But that amounts to saying that there is no meaningat all in life, which is ridiculous.

This is a debating trick that fails to address the topic athand in the interest of scoring points with the audience.

Straw personStraw person

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There are studies that show that vaccines are linkedwith autism.

So parents should have the right to opt out ofchildhood vaccination.

Cherry pickingCherry picking

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There are studies that show that vaccines are linkedwith autism.

So parents should have the right to opt out ofchildhood vaccination.

There is likely to be "evidence" for just about anything thatwe want if we look hard enough and ignore any evidence tothe contrary. But the question is what the evidence as awhole shows. Even a broken clock is right twice a day.

Cherry pickingCherry picking

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The government is trying to control us.

Fallacy of misplaced concretenessFallacy of misplaced concreteness

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The government is trying to control us.

People often talk about such abstract entities as "thegovernment," "the media," or "society" as if they wereconcrete things that could attempt to control us or doother nefarious things. In reality governments, the mediaand society are collections of particular individuals. Theymight coordinate their efforts, but then most groups aremade of individuals with different ideas and interests --good old "of�ce politics." Reality is much messier thansimple abstract nouns like these suggest.

Fallacy of misplaced concretenessFallacy of misplaced concreteness

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Rest on implied but unacknowledgedassumptions.

Stretch the evidence too far.

Depend on our willingness to �ll in the blanksand rely on mental shortcuts.


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There is no evidence linking asbestos to cancer.

Mere assertionMere assertion

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There is no evidence linking asbestos to cancer.

This is not even really an argument, but a simple statementoffered without evidence. It may seem like just statingsomething without argument would fail to convinceanyone, and yet there is nothing like repeating a simplestatement enough to get it stuck in people's heads.

Mere assertionMere assertion

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I know that ghosts exist because I have seen themwith my own eyes.

Begging the questionBegging the question

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I know that ghosts exist because I have seen themwith my own eyes.

While many people trust eyewitness testimony, thequestion here is how someone might know that what theysaw really was a ghost. This would require accepting theassumption that ghosts do exist, but isn't that what theargument is claiming to prove?

Begging the questionBegging the question

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There is no proof that the CIA did not assassinateKennedy and then cover it up.

That's why I think that they did.

Appeal to ignoranceAppeal to ignorance

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There is no proof that the CIA did not assassinateKennedy and then cover it up.

That's why I think that they did.

Conspiracy theories often rely on appeals to ignorance likethis. They shift the "burden of proof" to someone opposingtheir viewpoint without providing suf�cient evidence toprove their claims to be correct.

Appeal to ignoranceAppeal to ignorance

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Either you are on the reservation or you are off thereservation.

False dilemmaFalse dilemma

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Either you are on the reservation or you are off thereservation.

This is a quote from Richard Nixon, who in the last days ofhis presidency, believed that everyone who was notcompletely on his side was completely against him. Thereare, of course other options. Also known as the "black orwhite fallacy."

False dilemmaFalse dilemma

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Three Democrats I spoke with are opposed toabortion.

Thus all Democrats are opposed to abortion.

Hasty generalizationHasty generalization

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Three Democrats I spoke with are opposed toabortion.

Thus all Democrats are opposed to abortion.

This is clearly too small a sample size to provide evidencefor a claim about millions of people. Reliance on "anecdotalevidence" is another variety of this fallacy in that anecdotesreport individual cases that may or may not show a generalpattern.

Hasty generalizationHasty generalization

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If we allow human cloning, we'll end up with adystopian future like in the movie "The Island" whereclones are made just for "spare parts" and have norights of their own.

Slippery slopeSlippery slope

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If we allow human cloning, we'll end up with adystopian future like in the movie "The Island" whereclones are made just for "spare parts" and have norights of their own.

Alarmist claims about what will happen are hard to avoidsince we do tend to think of worst case scenarios. In thiscase, since a clone is nothing but an arti�cially producedtwin, raising a clone for its parts would be illegal andimmoral.

Slippery slopeSlippery slope

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When the coach yells at us for losing badly, we playbetter the next game.

When he praises us after a great win, we don't do sowell the next game.

SO negative reinforcement works, and positivereinforcement doesn't.

False causeFalse cause

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When the coach yells at us for losing badly, we playbetter the next game.

When he praises us after a great win, we don't do sowell the next game.

SO negative reinforcement works, and positivereinforcement doesn't.

Isn't a better explanation here that after playing eitherbetter or worse than average, the team typically returns totheir average performace?

False causeFalse cause

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You must be mentally ill if you commit a massmurder.

This is because only mentally ill people would dosuch a thing.

Circular reasoningCircular reasoning

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You must be mentally ill if you commit a massmurder.

This is because only mentally ill people would dosuch a thing.

Which explains which according to this argument: doesmental illness explain mass-murder or does mass murderprove mental illness? In either case no evidence is herepresented.

Circular reasoningCircular reasoning

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Also known as "motivated irrationality."

Result from the fact that our emotional andpersonal lives in�uence what we want to accept.

What we want can in�uence what we are willingand able to see.


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Wherever I look I see more evidence that theuniverse is governed by a malicious demon. Justconsider the evidence of epidemics and hurricanes!

Con�rmation biasCon�rmation bias

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Wherever I look I see more evidence that theuniverse is governed by a malicious demon. Justconsider the evidence of epidemics and hurricanes!

The problem here lies in not taking into account all of theavailable evidence. Good explanations of the data are notfound by looking only at evidence that appears to con�rmone's hypothesis.

Con�rmation biasCon�rmation bias

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Why did we torture those prisoners? Well the leadersassured us that it was for a greater good andeveryone else seemed to be going along with thattoo.

Group thinkGroup think

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Why did we torture those prisoners? Well the leadersassured us that it was for a greater good andeveryone else seemed to be going along with thattoo.

We often forget that we are fundamentally social beingsheavily invested in what (we think) others think of us. Onerotten apple can spoil the whole barrel.

Group thinkGroup think

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We really can have endless economic growth andprotect the enivornment at the same time!

Wishful thinkingWishful thinking

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We really can have endless economic growth andprotect the enivornment at the same time!

The old saying, "If it sounds too good to be true, it probablyis" applies here.

Wishful thinkingWishful thinking

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Also known as "unmotivated irrationality."

Result from "bugs" in our mental operatingsystems.

The mental shortcuts that we rely on don'talways work so well in certain contexts.


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This T-shirt is only 100 dollars! That is such a bargaincompared to the one selling for 1000 dollars youshowed me �rst!

Anchoring effectsAnchoring effects

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This T-shirt is only 100 dollars! That is such a bargaincompared to the one selling for 1000 dollars youshowed me �rst!

Even if nobody would pay such an outrageous price for a T-shirt just asking for such a price at the beginning ofnegotiations raises what we might later come to accept as afair price. This re�ects a bias towards information thatcomes �rst, regardless of its independent believability.

Anchoring effectsAnchoring effects

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If I happen to be rude to someone at the store, it isbecause I am stressed out by work pressure, but ifyou are it is because you are a jerk.

The fundamental attribution errorThe fundamental attribution error

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If I happen to be rude to someone at the store, it isbecause I am stressed out by work pressure, but ifyou are it is because you are a jerk.

When we account for our own behavior we have a (realistic)sense of the large in�uence of external in�uences, butwhen we asses other people's behavior we tend tooveremphasize their "internal" causes, how bad decisionsre�ect their true feelings and intentions.

The fundamental attribution errorThe fundamental attribution error

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I just heard the news about a terrorist hijacking aplane, so rather than �y to Florida I will drive.

The availability heuristicThe availability heuristic

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I just heard the news about a terrorist hijacking aplane, so rather than �y to Florida I will drive.

A heuristic is a "rule of thumb" that might work in somecontexts but fails in others. In this case even if a terroristicattack sticks out in one's mind, since it is dramatic, it is farmore likely that you will get hurt or killed in a car wreck.What is available to the mind is not always the same as whatis really more likely.

The availability heuristicThe availability heuristic

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Logical FallaciesLogical Fallacies

Logical FallaciesLogical Fallacies

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https://www.youtube.com/watch?v=4CtofTCXcYI

12 Cognitive Biases12 Cognitive Biases

12 Cognitive Biases Explained - How to Think Better and Mo12 Cognitive Biases Explained - How to Think Better and Mo……

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https://www.youtube.com/watch?v=wEwGBIr_RIw

Find out moreFind out more

Your Logical Fallacy Is: A well designed website with good examples of a varietyof fallacies.

Your Bias Is: By the creators of Your Logical Fallacy Is, this site is devoted tosome important cognitive biases.

Logically Fallacious: a comprehensive list of hundereds of types of fallacies andbiases.

Fallacies: The Internet Encyclopedia page on logical fallacies has anothercomprehensive list.

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https://yourlogicalfallacyis.com/

https://yourbias.is/

https://www.logicallyfallacious.com/tools/lp/Bo/LogicalFallacies

https://www.iep.utm.edu/fallacy/

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