4 Fallacies - ZipWits

wonky thinking; defective reasoning

Fallacies are attempts at inference, but defective one way or another. They contain an error in reasoning, often in the connection of cause and effect. For example, our team is sure to win since I’m wearing my lucky cap.

Goals

Describe in general terms what makes an argument defective
Explain the influence of emotions on validity
Recognize instances of a variety of fallacies and non-fallacy
Describe what makes an analogy weak or strong

Influence by Emotion

A fallacy is a defective argument, meaning it has an error in reasoning.

A formal fallacy has a defect in its logical structure. That is, the form of the argument does not fit one of the deductive patterns.
An informal fallacy has no recognizable deductive form; it can only be detected by examining the content of the argument, for instance to find that the premises are not relevant to the conclusion.

In fallacies of emotional influence, the premises are not relevant to the conclusion.

In an effective argument, the premises support the conclusion.
In fallacies of emotional influence, the arguer uses some sort of emotional appeal to make them appear relevant.

In an appeal to emotion, the desire for esteem or avoid sorrow is reason for a belief or action.

Esteem may be desire for flattery, popularity, pride, sense of inclusion, or other personal affirmation.
Sorrow can be the wish to avoid confusion, threat, disgust, or other feelings of discomfort, but emotion is not relevant to whether the proposition is true or false

Appeal to fear: the desire to avoid likely harm or discomfort is reason for a belief or action.

This variety of emotional appeal uses threat to cause a reluctant person to do something. • In this neighbourhood we give expensive treats for Halloween. It is still cheaper than removing rotten eggs or spray paint.
The coerced party acts out of fear of harm rather than out of reasoned persuasion. • My cousin signed the contract without understanding all the legal jargon, but not wanting to feel awkward asking what this word or that means.

In an appeal to pity, feeling sorry for the suffering of others is reason for a belief or action.

The job should go to Logan. Logan is a single parent with a couple kids to care for and was recently robbed.
Listen, I didn’t mean to make you cry, but you have lots of toys at home. No, not again. Okay, just the teddy bear, okay?

In appeal to praise, the desire for the approval of others or acknowledgement of self-regard (vanity).

You work long and hard and deserve a little fun in the sun. Book now for our bonus vacation package.
You’re smart. When smart people shop, they shop at our store.

In appeal to inclusion, the desire to not be left out of a group is reason to act or believe as others do.

Folk Rock has to be the purest form of musical ballad. Just listen to the applause from the audience.
I have to have cranberry sauce at Thanksgiving because that’s what all my relatives serve. It’s like I would be celebrating a different holiday than everyone else.

In appeal to spite, the desire for revenge is reason to support a belief or course of action.

I see your shoelace is untied and she might trip, but I won’t tell you. You poke fun at others. It would be nice to see you get a little comeuppance.
I see no reason to help your cousin move his furniture to his new apartment. When I moved last week and asked for help, he seemed to ‘discover’ that he had to work.

A personal attack finds fault with a person as a basis for rejecting his or her belief.

Mikey has a lava lamp and Mikey’s a dweeb, so no thanks, I’m not going to have a lava lamp in my room.
No, the album isn’t great. Nobody but an idiot would listen to her music.

Circumstantial: claims the other person is motivated by a bias or hidden agenda.

You want us to outlaw plastic shopping bags as bad for the environment. But isn’t it true you have relatives who work for a pulp mill that makes paper bags.
Logan argues that the fairest kind of income tax is a ﬂat tax: everybody pays the same amount. But Logan is a billionaire and stands to save millions of dollars if a ﬂat tax is enacted, so we can’t take Logan’s argument seriously.

You Too (Tu Quoque) claims the other person is a hypocrite who fails to practice what he or she preaches.

Dad, I don’t see how you can ask me to not smoke. You and mom both said that you smoked when you were young. Maybe I will quite later on, like you did.
The ambassador’s complaint about poverty in our nation is ridiculous since twice as many people are below the poverty level in his own country.

What do you think?

We all want to feel good, or at least not bad. So why isn’t an emotional argument valid?
Commercials show us sad children living in poverty and ask for money. Is that a humanitarian cause or appeal to pity — or can it be a bit valid and a bit wonky?

Influence by Imitation

In these fallacies, the character of others is taken as sufficient reason for belief or action.

The status of the messenger rather than the merits of the message justifies the conclusion.
We are influenced to be like them or do like them.

In appeal to authority, regard for the person making an endorsement is the reason for belief.

A claim is considered true because of who says it is, such as celebrity endorsement of a product. The celebrity is a perceived expert.
Just as personal attack rejects a claim because the person making it is reviled, appeal to authority accepts the claim because the person making it is revered.

It is a fallacy because regard for the arguer is not reason to accept or reject the argument.

The perceived authority or witness might not be qualified, might have a bias, a motivation to distort the truth, or might not able to perceive or recall the facts.
There is a motivation to believe like them in order to be like them.

Belief is based on that which is outside the expertise of the person making the endorsement.

Brand X is a smart choice in toothpaste because Einstein used it.
The best view I ever heard on this was told to me by a simple, honest woodcutter. He stared reflectively in the sky, then looked at me with quiet eyes. “Although poor myself,” he said, “I always reckoned that deficit spending by the government could stimulate the economy.

Two wrongs make a right: that others do or would do wrong is reason for us to act likewise.

Hey, that van just cut right in front of us. Speed up and cut him off. He needs to know what it is like. Dangerous drivers need to be taught a lesson.
The cashier wouldn’t say anything if I overpaid, so if the cashier charges too little I’ll keep it.

‘Two wrongs’ thinking is: if one mistake is made, another can cancel it out.

She pinched me, so I pulled her hair.
The library keeps calling me in their fundraising campaign. I’ve asked them repeatedly to stop. If they don’t stop, I will rip pages out of books before I return them. I’ll make sure that they’re the pages with important plot points.

This fallacy does not include, however, retribution and preemptive strike.

Punching a mugger or shouting to break up a fight.
A naval blockade to prevent nuclear hostilities.

Appeal to tradition is to do as we’ve always done is reason to continue to do so.

This fallacy supposes something is good or right because it is familiar. • Stovetop hot cereal – old-fashioned goodness just like grandma used to make.
If something fits with historical practice, then it is considered true or appropriate. • No, son, you are not having a car. I never had an automobile, my father never had one, and nor did his father before him. Yet we always got where we were going.

Age of a belief or practice may make it more familiar, but that alone does not make it correct.

A long-held false belief that the world is flat — false.
Ancient practice of blood-letting to reduce fever — also false.

Appeal to novelty: being new or newer is reason to believe that it is true or good.

Brand X soft drink – new, improved package, same great taste.
Ya gotta have the latest smartphone. The ‘chameleon’ covering takes on the colour of what it touches. Same functionality as our previous model, but with the latest, must-have covering.

Another version (“non-anticipation”) argues that since an idea is not already part of current wisdom is reason to reject the idea.

If salt is as harmful as claimed, it would have been banned from food long ago.
We don’t need email. Telegrams were good enough when my grandfather ran the company.

What do you think?

Celebrity endorsement is big business. What makes people so likely to purchase products endorsed by sports stars?
When politicians try to persuade voters, is that exercising influence by imitation? My political party can make your life better, so vote for us.

Presuming a Premise

The fallacies in this group take a premise for granted rather than proving it.

Each of these fallacies uses a logical operator to distract from the apparent falsehood of a proposition.
In a false dichotomy, that operator is OR. That one option is undesirable is reason to chose its only apparent alternative.

False dichotomy presents two options as if they were the only ones available, one of which is undesirable, so the best choice is the alternative preferred by the arguer.

The fallacy has the form of a disjunctive syllogism: A or B; not A; therefore, B. • Either you are part of the solution or you are part of the problem.
It is a fallacy because these choices might not be the actual options or they might not be the only options. • They can send a man to the moon, so why can’t they cure the common cold?

This is also known as the either-or fallacy and black-and-white thinking. The fallacy is intended to limit choice; it leaves out relevant alternatives.

Use Brand X deodorant or risk perspiration odour. Nobody wants to smell like a pig, so use brand X.
There are two types of people in this world: the rich and poor. Do you want to get rich, or are you happy to be poor?

In the fallacy of appeal to ignorance, the absence of proof to the contrary is reason for a belief.

This has the form of a disjunctive syllogism: A or not A; not not A; therefore, A.
It is a fallacy because it counts lack of proof as proof to the contrary.

In appeal to ignorance, whatever hasn’t been proved false must be true, and vice-versa.

We know no life exists on other planets because every attempt to establish their existence has failed.
There is no conclusive study that says taking vitamins actually improves a person’s health. Therefore, we can conclude that vitamins are simply a waste of money.

Generally, whoever wishes change has the burden to supply reasons for change. There are a couple special cases, however.

If qualified investigators search for something and fail to find it, then this may imply that there is nothing to be found.
Furthermore, a person not proven guilty is considered innocent.

Slippery slope: claim that an option will lead to an undesirable result is reason to act otherwise.

Don’t donate to any charity or before long they will all be after your money.
Slow down a bit. If you are too efficient, the boss will soon expect more from all of us.

Slippery slope holds that an action will inevitably lead to a certain result, that result is undesirable, so do not take the initial action.

This similar to hypothetical syllogism: if P, then Q; if Q, then R; R is undesirable, so do not do P.
If you spray to get rid of mosquitos, the dragonflies and frogs will starve, then the snakes and owl that live on them and soon the whole local ecosystem will fall apart.

But Slippery Slope is a fallacy since the chain of events is unlikely and is presumed, not proven.

I am against lowering the drinking age from 21 to 18. This will only lead further demands to lower it to 16. Then it will be 14. Before we know it our newborns will be suckled on wine rather than mother’s milk.
If we ban smoking, people will turn to soft drugs, then move on to hard drugs and the crime rate will go up; so to prevent crime we should allow smoking.

What do you think?

“Try it, what have you got to lose?” If said in a medical context, would that be an instance of appeal to ignorance?
Are online messages by officials an exception to slippery slope? For instance, could the following be argued validly? “Even though his postings are offensive to just about everybody, we cannot remove them or eventually we will be throwing out everyone’s freedom of speech because somebody objects.”

Presuming the Conclusion

In fallacies that presume the conclusion, the premises might provide some support but not enough to believe the conclusion.

Begging the question is a fallacy in which the conclusion restates one of the premises.

The conclusion is the proposition to be proven. In fallacies in this group, the conclusion is presumed in the premises,
The conclusion is hidden in the premises usually in synonyms or paraphrase.

It is a fallacy because the reasons or evidence are not independent of the claim; the conclusion just restates a premise which is presumed.

The reason there is such a big demand for the latest technology gadgets is because everybody wants them.
Telepathy cannot exist since the direct transfer of thought between individuals is impossible.

In a complex (or ‘loaded’) question, the conclusion is presumed within a question.

Where did you hide jewels you stole? — Even answering “nowhere” presumes that you stole the jewels, but just did not hide them.
Timmy, do you want to put your toys away in the box or on the shelf? Would you prefer to take your nap now or after your cocoa? — Timmy is merely told to ‘put away your toys’ and ‘take a nap’ even though he seems to have a choice in the matters.

The question implies a hidden ‘yes’ response, so this is a type of begging the question.

The classic loaded question is: are you still beating your wife?
Similar is: are you in favour of the horrible budget that the mayor proposes?

Respond to a complex question by answering its component questions separately.

Why did you make your husband alter his will in your favour? How did you put poison in his coffee without attracting attention?
I see you aced that last test. In fact, you’re doing well in all subjects this term. Have you stopped cheating on exams?

The fallacy of suppressed evidence leaves out what would lead to a different conclusion.

Let’s get a bulldog puppy for the kids. They are ugly-cute and nobody around here already has one. — This is a one-sided assessment since bulldogs are not especially good around children, difficult to train, and have habits of drooling and breaking wind.
This ad says that we can buy a Brand X cell phone for only $99. That sounds like a great bargain. For less than $100 we can make all the phone calls we want!

Suppressed evidence allows only the facts that support the conclusion.

Let’s not vacation in Port Spindrift. Think of the heat, the mosquitoes, and the crowds. [I need not mention, on the other hand, the sunshine, low costs, excellent food, and variety of entertainment.]
Opening an iced-tea franchise in China is a great idea. They have the population for lots of customers. They already like tea and it can get hot in many regions of China. [However, they already have an established market for the product, communist party regulations oppose foreign investment, and iced-tea might not meet cultural acceptance.]

If deliberate, the suppression is one-sided and omits evidence to the contrary.

Port Spindrift has schools, jobs, shopping, recreation facilities, and reasonable housing costs. It is clearly a great family town. [Oh, forgot to mention frequent public service strikes, traffic congestion, pollution, and the high crime rate.]
I’m not going to get married. There would be all that extra responsibility, not to mention the loss of my freedom. Think of the costs of raising children and putting them through school. Then there are the increased insurance premiums. [Fails to consider the merits of marriage.]

In a balanced assessment, by comparison, the evidence is reason for a belief or action.

This is a process of inferring a conclusion by weighing reasons for (pro) and against (con) to reach a decision based on the greater body of evidence.
Suppressed evidence is a fallacy, while a balanced assessment is a method of induction.

What do you think?

“This little gem is only 10 years young, but the odometer reading is very low, so it is surely in good shape.” What evidence might the used-car sales rep be suppressing?
Some people say “that begs the question” — meaning the discussion raises a question. What is the difference between “begging the question” and “that begs the question”?

Evading the Issue

Straw-man presumes to refute an opposing belief by refuting a misconstrued version of it.

You think cloning in the biology lab isn’t a problem. Suppose you were cloned, like a toy soldier. Would your clone have rights. Could he or she claim your property? These are deep problems best avoided. [Distorts the original argument about the cloning of frogs by extending it to the cloning of humans.]
You want a guaranteed income for every adult — half of minimum wage. No. Any society with unrestricted access to funds loses its work ethic goes only for immediate gratification. If people lose their incentive to work, who will do the essential jobs? [Changes the topic of guaranteed income into an argument abut work ethic.]

Straw-man sets up a different version of the argument, one that is easier to attack.

Distort the original argument, refute the distorted version, claim the original position is refuted.
This is a fallacy because rejection of a distorted version of a position does refute the original position.

Runaway-train is a version of straw-man that goes to extremes.

You agreed to allow a bingo hall in the town because people should have the choice to gamble if they so wish. I’m now proposing to have gaming machines on every street corner for precisely the same reasons.
The opposition wants to lower the highway speed limit by 10% in order to save lives. But why stop there — why not lower it 50% or more and save more lives?

Missing the point draws a conclusion different from the one logically implied by the premises.

Members of the jury, clearly the defendant is guilty. He has been in and out of trouble. As a youth he was suspended for truancy, as a teen he was ticketed for speeding, and as an adult he has had his taxes audited. Now he stands here guilty of murder. [The issue is whether the accused is guilty of murder; the argument ignores this and proves that the accused had some concerns growing up.]
Nuclear power plants generate electricity, but electricity can be dangerous no matter where it comes from. Every year people are accidentally electrocuted. Most accidents are the result of carelessness and could easily be avoided by using common sense. So no, nuclear power isn’t dangerous. [Makes a connection that being careful can reduce the number of electrical accidents, but misses the issue of whether nuclear power is dangerous.]

The evidence implies one conclusion, but the arguer draws a conclusion not implied by the premises. Also known as “ignoring the issue.”

Most car accidents occur within 50 kilometres of one’s home. Apparently, it is more dangerous to drive close to home than far away from home. [Missing the point that most people live and work within 50 km of home.]
She is suffering from amnesia and has no recollection of events. We can only conclude that she did not commit the burglary last week ago, as she has been accused of doing. [Missing the point that not remembering does not exclude having committed the crime.]

Changing the subject (a.k.a ‘red herring’) is a pretence of refuting by diverting attention.

Is nursing a worthwhile career? Believe me, we not only work as hard as anyone else, but harder. The hours are long, the demands are many, and you have to keep current with medical changes. [Which changes the subject: it may be hard work, but is it worthwhile?]
What have I done to improve security? I am committed to protecting our great nation, which is more than my predecessor managed. When I came into office, the cupboards were bare and I had to restock all the supplies. [Changes the subject from what you will do to what the previous administration may or may not have done.]

Changing the subject responds by diverting attention from the evidence and, in doing so, claims to have defeated the other person’s argument.

You think too much television is the reason kids can’t read and write? I don’t agree. Many of today’s TV shows are excellent. On reality shows, people to use their wits. Sit-coms give comedy relief from everyday stress. Drama programs add a sense of excitement and adventure. Today’s television is great.
She have masterminded the crime. I have proved beyond a shadow of doubt that she was not even in the country at the robbery. [The client may have ordered the crime before leaving or arranged it by telephone.]

What do you think?

How does the following response evade the issue? “Why do we have more crime in this region? Because we keep statistics. We have the best statistics. We keep more statistics on crime than any other region. If you don’t keep records, you don’t find crime. It only looks like we have more crime because we keep such great records. I say, keep fewer stats.”
Politicians are notorious for evading the issue, especially in questions from members of the press. How might a straw-man fallacy be politically used to knock down an issue that members of the public find complicated or technical?

Hasty Conclusion

Accident: an extreme exception to a general rule is still reason to reject the rule as inadequate.

Cutting people is a crime; surgeons cut people with scissors and knives; so surgeons are criminals.
Freedom of speech is the law of the land. Therefore, your friend was acting within his rights when he shouted ‘‘Fire! Fire!’’ in that crowded theatre, even though it was only a joke.

Accident seeks to reject a general rule by pointing out an exceptional case as evidence of the rule’s inadequacy.

Accident is similar to refuting an argument showing a counter-example.
However the fallacy of accident treats the general rule as rigidly absolute and offers an exception that is an impractical extreme or applies the rule under circumstances that make the rule irrelevant (meaning the rule does not apply when other factors are taken into account).

Some people use the phrase “an exception that proves the rule” incorrectly.

To ‘prove’ used to mean to ‘test’ or establish quality, such as in proving the temper of a sword. The phrase “an exception that proves the rule” uses ‘prove’ in this sense.
The exception puts the general rule to the test. If the exception has merit, then it refutes the rule.

Accident is also known as ‘hasty instance’ in that it is quick to find an exception.

The sign says ‘no parking’ so the ambulance should not park here.
You say we have a duty to repay what is owed. Suppose a man lends you a rife for hunting, goes insane, then asks for the rife back? It would be wrong to put a lethal weapon into the hands of a madman, so you’re wrong – we don’t have a duty to repay what is owed.

A variation of accident is “accent” or shift in emphasis.

Accent interprets the rule narrowly and changes the meaning of the rule by changing stress on a key element. • Mother said we shouldn’t throw stones at crows, but didn’t say anything about throwing apples.
This can seem to make a prohibition more permissive. By stressing the factor to be excluded, it implies that all else is admissible. • True, we promised not to invade far away lands, but your country is not very far away.

Hasty generalization concludes a generalization from a sample that is too small or not typical.

Age 70 is too old to drive; my aunt became reckless on the road in her late 60s.
All this snowfall in November is sure to mean we are in for a viciously long winter.

Hasty generalization concludes a generalization about a population based on a sample that is not typical of the population.

The sample may be too small or the sample might be an exception to a general rule.
In any case, the sample observed is not representative of a population.

The sample needs to be large enough to represent the population’s diversity.

Spaghetti boiling in a pot is fairly homogenous; testing whether one strand is done is sufficient.
People, however, are more diverse than strands of spaghetti.

Proof by example — a form of hasty generalization — goes from example to generalization.

Rover likes carrots, so dogs like carrots.
It would be valid only of it proceeded from an example to an instance (not a generalization): Rover likes carrots, so some dog [or there is a dog who] likes carrots.

What do you think?

How do you know when a sample is large enough to avoid hasty generalization?
Is looking for a loophole similar to finding an exception as in accident or accent? The contract says payment in cash on delivery, but the company accepted my credit card, so the contract is invalid and I want my money back.

Ambiguity

In the fallacies of ambiguity, a word or phrase is used unclearly or not consistently. The premises cannot support the conclusion since they refer to different senses or interpretations.

Amphiboly draws a conclusion based on an ambiguous arrangement of words.

Logan said that he went out on the veranda and watched the ﬁreworks go up in his pyjamas. Logan must have had an exciting evening (and pyjamas).
The travel brochure states that walking up Main Street, the kinetic statue comes into view. Apparently that statue has no trouble getting around.

In amphiboly, a premise can be interpreted in more than one way due to its word-arrangement or punctuation.

The conclusion is based on the more unlikely interpretation. • The supervisor told my client that he made a mistake, which shows the supervisor has the courage to admit making mistakes. [Does ‘he’ refer to the supervisor or to the employee?]
The premises can’t support the conclusion since they refer to different interpretations. • The will states: ‘‘I leave my house and my dog to my niece and nephew.’’ The niece claims she alone owns the house. The nephew claims the property and pet pass to both of them jointly.

In equivocation, the conclusion depends on the inconsistent use of a word or phrase.

An athlete is a human being, so a good athlete is a good human being. [Equivocation on “good” as successful or virtuous.]
Emeralds are seldom found in this country, so you should be careful not to misplace your emerald ring. [Equivocation on “found” as indigenous or located.]

Equivocation arises from the ambiguity of a word or phrase used by the arguer.

A word or phrase is used one sense in the premises.
The same word or phrase is used in a different sense in the conclusion.

The premises cannot support the conclusion since they refer to different senses.

You have a duty to do what is right. You have a right to leave the country. So you have a duty to leave the country. [Equivocation on ‘right’]
Good steaks are rare these days, so don’t order yours well done. [Equivocation on “rare”]

What do you think?

A letter of recommendation reads: “anyone who gets Logan to work for him will indeed be fortunate. Work ethic, why he doesn’t care how many hours he must put in. All in all, I cannot say enough good things about Logan or recommend him too highly.” How might this be an equivocation and the letter not really a recommendation?
Comedian Steven Wright is known for humorous use of ambiguity. “I went to a restaurant that serves breakfast at any time. So I ordered French toast during the Renaissance.” Create your own humorous ambiguity.

Fallacies of Category

Fallacies in this group assume that the whole is equivalent to its parts or vice versa.

Composition: claims that something has a property because its parts have that property.

Molecules are in constant random motion. The statue of the lion outside the library is composed of molecules. Therefore, the statue is in constant random motion.
Each page in this large phone book can easily be torn in half, so the phone book can easily be torn in half.

If the parts have a certain property, then the whole must have that property.

The parts of the model are plastic, so the assembled airplane is plastic. Every part of the model can fit in its package, but it does not follow that the assembled airplane can fit in its package.
Atoms of an apple have mass, so the apple has mass. Every atom of the apple is invisible, but it does not follow that the apple is invisible.

As with the fallacy of division, the error is in transferring attributes that cannot be transferred.

The sports car is made of lightweight parts, so the car itself has a low mass. [Each part is light, but there are so many that the vehicle as a whole is heavy.]
A government represents its people, people can be phoned, so a government can be phoned. [I tried to phone the government, but people kept answering.]

The ‘expansive property’ is an exception to the fallacy of composition. If every part of a whole has an expansive property, then the whole will, too.

Plastic and yellow are expansive properties, so if all the parts of a model airplane are plastic and yellow, then the model will also be plastic and yellow.
Light and cheap, by comparison, are not expansive properties. Individual part might all be light and cheap, but the product is nevertheless heavy and expensive.

Division: concludes that the parts have a property because the whole has that property.

Russia is big, so Russians must be big.
If you like cake, you will like to eat its ingredients, such as raw eggs, butter, and flour.

The fallacy is assuming that what is true of a whole must be true of each of its parts.

You claim to be bankrupt, but you work for a wealthy company, so you must be wealthy.
People are made of cells. Human beings are conscious, so cells must be conscious.

As with the fallacy of composition, the error is transferring properties (sometimes with humorous results) that cannot be properly transferred.

An expectant Irish couple with two children are nervous, because they know that every third child born is Chinese.
White sheep eat more than black sheep because there are more of them. Therefore, this particular white sheep eats more than that black sheep.

What do you think?

“We saw marching bands, clowns, horses, and floats, but the parade never passed by.” This commits the fallacy of composition. The parade is not in the same category as the marching bands, clowns, horses, and floats. Is the mind in the same category as thoughts, memories, and emotions?
Is this correct or is there some fallacy of category? “Every cell in my body is 90 percent water, so my body is 90 percent water. The moon has an effect on bodies of water. Therefore, the moon has an effect on me.”

False Cause

Post hoc: one event is the cause of another because when one event occurs, the other occurs.

Roosters crow just before the sun rises. Therefore, roosters crowing cause the sun to rise.
We had a pile of rags in the corner. Pretty soon we noticed rats hanging around the pile of rags. Rags cause rats.

Post hoc is a fallacy because sequence does not entail cause; the two events are coincidence.

Post Hoc is from the Latin phrase “post hoc, ergo propter hoc” which means “after this, therefore because of this.”
Because one event follows another, it is claimed that the second has been caused by the first.

Post Hoc is the basis of good-luck charms, superstition, sports rituals, and magical thinking.

I should get this job because it is meant to be. There are a lot of out-of-work musicians, but I was playing on the corner for coins when a gust of wind blew the newspaper in my face with your job posting literally right before my eyes. That means getting this job is destiny.
Jones decided to become a tele-healer, guaranteeing to heal over the phone, results guaranteed for cold or influenza within two weeks.

Joint effect: false cause in which the two events result from an underlying cause.

Sales of soup are highest when the incidence of frostbite is the highest, so soup sales cause frostbite. [Both are the result of cold weather, causing more people to consume warm foods and be injured by exposure to cold weather.]
For generations now there has been a trend: during an election year consumer spending increases, compared to spending in non-election years. Evidently, elections make people spend. [Governments seeking re-election tend to keep taxes down in election years. Lower taxes mean greater discretionary income to spend.]

Joint effect is a fallacy since two events are not related as cause-effect, even though they correlate as both “symptoms” of an underlying cause.

You had a fever, then broke out in spots, so the fever caused the spots. [No, both fever and spots are symptoms of the measles virus.]
When I eat chocolate, I get a headache, so chocolate causes a headache. [No, there could be an underlying cause of both. For instance, I only eat chocolate when I feel stress and stress causes muscle tension, which results in a headache.]

In gambler’s fallacy, a streak of events is reason to believe a contrary outcome is due to happen.

The value of company stock has gone up for several days. Sell now, because what goes up and up must come down.
Your last two blind-dates turned out to be awful, but third time’s a charm. This one will be wonderful.

The longer the run, the stronger the belief that the opposite outcome is due to occur. But it is a fallacy when previous results have no bearing on the outcome of next event.

Our team has never won a championship, so we’re due this season.
After ten tosses the coin has only been tails-up, so the next flip will be heads-up.

What do you think?

People tend to feel the need for agency, the ability to have an effect on the outcome. Without it we may feel helpless or victims of circumstances. But how does that explain the ritual of putting on a souvenir team hat and rooting for the team to win while watching a recording of the game from yesterday?
In a certain region, literacy rates have steadily declined since smartphones became common. Is it possible to conclude from this correlation that the smartphone impedes learning?

Non Sequitur

“Non Sequitur” is Latin for “it does not follow.” In these fallacies the conclusion does not follow from the premises. All formal fallacies are special cases of non sequitur since their form is defective.

Affirm the consequent: that the consequent is true is reason to believe the antecedent is true.

An egg is broken. If I drop an egg, it breaks. Therefore I must have dropped it. –But there could have been other causes. Perhaps someone else dropped it or the chick popped out.
When cats are bitten by rabid raccoons, the cats die. We found a dead cat by the roadside so there must be a rabid raccoon around here.

Affirm the consequent is a fallacy because an event can be produced by different causes.

To have a fire, there must be oxygen. There is oxygen here, so there must be a fire.
If the mill is polluting the river, then the number of fish deaths will increase. In fact, fish deaths have increased. Therefore, the mill is polluting the river.

Affirm the antecedent (a.k.a. modus ponens) is valid; affirm the consequent is invalid.

If two objects have mass, then they mutually attract; the Earth and its moon each have mass; therefore the Earth and moon attract one another. Affirm the Antecedent, valid. If A if true, then B is true; A is true; therefore, B is true.
To have a fire, there must be oxygen. There is oxygen here, so there must be a fire. Affirm the consequent, invalid. If A if true, then B is true; B is true; therefore, A is true.

Deny the antecedent: that the antecedent is false is reason to believe the consequent is false.

If I am in the ocean, then I am in water; I am not in the ocean, therefore I am not in water. [I could be in a river, pool, or bathtub.]
Meditation is relaxing, but I am not meditating, so I am not relaxing. [I might be doing some other relaxing activity, such as reading or soaking in a hot tub.]

Deny the consequent (or modus tollens) is valid; deny the antecedent is invalid.

If there is fire, then there must be oxygen; the sun has no oxygen; so the sun is not on fire. Deny the consequent, valid. If A if true, then B is true; B is not true; therefore, A is not true.
If it is raining, my puppy will be soaking wet. It isn’t raining, so my pup isn’t wet. [In fact, she is; she’s having a bath by the dog groomer.] Deny the antecedent, invalid. If A if true, then B is true; A is not true; therefore, B is not true.

Maybe both: that one alternative is true is reason to believe another alternative is false, when both options could be true.

I am at home or in the city. I am at home, so I am not in the city. [Could be both if my home is a city apartment.]
Would you like cream or sugar with your coffee? Cream—okay, then no sugar for you. [Perhaps I would like both cream and sugar in my coffee.]

Maybe both (a.k.a. “affirming a disjunct”) is a fallacy when both options could be true.

The list of alternatives does not exclude the possibility of both A and B being true.
There may be more options available, even if unstated.

Disjunctive syllogism (excluded middle) is valid; maybe both is invalid.

She paid Pete or Paul; she didn’t pay Peter; so she must have paid Paul. Disjunctive syllogism, valid. A or B is true; A is not true; therefore, B is true.
My puppy is house-trained or there is an accident to clean up when we get home. My puppy is house-trained, so there will not be pee on the carpet [Perhaps the pup is housebroken, but has a bladder problem or drank too much water.] Maybe both, invalid. A or B or C is true, A is not true; therefore, B is true.

Maybe neither: that one alternative is false is reason to believe the alternative is true.

It can’t be both sunny and overcast. It is not sunny; therefore, it is overcast. [Could be neither; clear sky in the middle of the night.]
The missile can’t go both north and south. It wasn’t fired north, so we must be going south. [Maybe Neither, it is headed east or west.]

Maybe neither (or “denying a conjunct”) is a fallacy when the list of options does not include the possibility of both A and B being false.

It could be not A or not B or neither.
There may be more options available, even if unstated.

Note that not (A and B) is the same as not A or not B.

Disjunctive syllogism is valid; maybe neither is invalid.

The coffee pot was left on or off. It wasn’t left on, so it must be off. Disjunctive syllogism, valid. A or B is true; A is not true; therefore, B is true.
A suspect cannot be guilty and have an alibi. Since you don’t have an alibis, you must be guilty. [Could be innocent, but without evidence that you were elsewhere.] Maybe neither, invalid. Not A or not B or C is true; A is not true; therefore, B is true.

Undistributed middle: that subjects have the same predicate is reason to equate the subjects.

The pope is a person. I am a person. Therefore I am the pope. [The pope and I have the same predicate: being a person, but that does mean we are the same subject.]
Men are human; women are human; so men are women. [Men and women have the same predicate: being human, but that does mean men and women are the same subject.]

A valid syllogism leaves out the middle term of the premises.

Spot is a dog; a dog is a mammal; thus, Spot is a mammal. [The middle term ‘dog’ is left out.]
Dragonflies are insects that eat mosquitos. No insects that eat mosquitos should be harmed. Therefore no dragonflies should be harmed. [The middle term ‘that eats mosquitos’ is omitted.]

However, undistributed middle is a fallacy.

The subjects have a common property (predicate).
But, the subjects can be separate groups (categories)

What do you think?

All living things can reproduce. A virus can replicate. Is a virus is alive?
There is an old puzzle that goes like this. The king held out a basket with two notes. If the knight picks the one marked Yes, he may marry the princess. The knight, suspecting both notes are marked No, grabbed a note and swallowed it, proclaiming that he picks the note remaining in the basket. Which non-sequitur applies to the puzzle?

Weak Induction

In an induction, the premises support the conclusion but do not guarantee it. The conclusion is said to have a degree of strength: weak or strong. A strong induction whose premises are true is said to be cogent.

In an analogy, one case (that is, an object or situation) has a certain property because it is like another case that has the property and the two are alike in ways relevant to that property.

An analogy is strong when the cases compared share a large or decisive number of relevant similarities and do not exhibit significant differences.
An analogy is weak when the cases compared do not share a large or decisive number of relevant similarities or do exhibit significant differences.

In a weak analogy, similarity in one respect is reason to expect similarity in other respects: known parts are similar, so unknown parts must also be similar.

The red laxative capsule looks like the blue jelly bean, so it will be just as tasty.
When water is poured on the top of a pile of rocks, it trickles down to the rocks on the bottom. Likewise, when rich people make money, it will trickle down to the poor.

An insignificant cause is genuine, but minor compared to more important factors.

Painting the restaurant’s dining room may attract more customers. [Yes, but advertising and lower prices are more effective.]
You shouldn’t leave your porch lights at night. It contributes to global warming. [True, but the effects of the automobile and industrial emissions are more significant.]

Over-simplification see an either-or, when in fact there are other contributing factors.

The sales of video games are down, so software piracy must be the cause. [Slumping sales could be due to economic recession, no new games, or competing technology.]
Our airplanes are so well built that the aviation accident must have been the result of pilot error. [The accident could have been caused by collision with a bird, bad weather, terrorism.]

What do you think?

If an automobile breaks down on the freeway, a passing mechanic is not obligated to stope and help out with emergency road service. For similar reasons, if a person suffers a heart attack on the street, it would seem that passing physician is not obligated to render emergency medical aid. Yet, in fact, a physician is held to a higher standard and took an oath. So is the analogy strong or weak?
Our roadways have been eroding for years. We need to stop using salt on roads in winter. Or is that over-simplifying the situation?