30 Common Logical Fallacies–A Study Starter

What is a logical fallacy?

Nothing is more frustrating than debating somebody who has no idea what they’re talking about. Well, actually there is. It’s even more frustrating to debate somebody when you, yourself, have no idea what you’re talking about. So what must you do to avoid these frustrations? You can start by getting to know the most common logical fallacies.

A logical fallacy is an argument based on faulty reasoning. While fallacies come in a variety of forms, they all share the same destructive power, namely, to dismantle the validity of your entire argument. Whether you’re building a case for a position paper, engaging your classmates in a lively debate, or storing up pithy political one-liners for your next Twitter war, you need to know these common logical fallacies.

But first...

What is Logic?

Logic describes the rules and principles for making correct arguments and avoiding incorrect arguments. Logic is a key branch of philosophy, and logic students learn how to analyze and appraise arguments. In logic, certain valid rules of inference must be acknowledged and adhered to in order for an argument to be considered legitimate. Logic attempts to take us from truth to truth. In deductive logic, the truth of premises guarantees the truth of conclusions. In other types of logical inference (such as with inductive logic), the point is to make the conclusion more probable based on the truth of the premises.

Logic acknowledges the shared truths among us and guides us to uncover new truths. Logic is therefore the very fabric of meaningful debate. Without logic, human inquiry grinds to a standstill because we have no reliable way to build our knowledge based on previously uncovered truths.

What is a Logical Fallacy?

Logical fallacies are bogus modes of reasoning that can appear legitimate but in fact violate accepted rules of inference. Logical fallacies can be tricky. By masquerading as legitimate arguments, they can fool us into thinking that they are legitimate. But closer inspection reveals the critical flaw at the heart of any given logical fallacy. Such flaws are not always easily detected, especially in the heat of debate.

To confound matters, logical fallacies often have an element of truth. But the truth gets misused by faulty logic so that the desired conclusion is not properly justified. A fallacy may even reach a true conclusion, but by arriving there in the wrong way, render the conclusion unconvincing. Moreover, fallacies aren’t always driven by the desire to deceive or manipulate. Fallacies can also be rooted in bias, emotion, or misunderstanding, which can sometimes be less immediately apparent.

Why are logical fallacies so common? The answer is simple: they work! To say that logical fallacies work does not mean that they help us gain knowledge or insight into truths about the world. Rather, it means that bogus types of reasoning are often amazingly effective at getting people to believe things that they shouldn’t believe.

Lawyers, politicians, and marketers often have the keen ability to use fallacious arguments as weapons. This is rarely an accident. Unfortunately, when people want to believe something, they’ll often enlist logical fallacies to help convince themselves and others of its truth. Clear, careful, and critical thinking, therefore, requires calling out logical fallacies.

Broadly speaking, logical fallacies fall into two categories:

• Informal Fallacies, in which what the argument says, or how it says it, is flawed; and
• Formal Fallacies, in which the step-by-step progression or “form” of logical reasoning in an argument is flawed.

Why Does It Matter?

Detecting the flaws in an argument is important. Sure, identifying the flaws in an argument can be personally gratifying by helping you win a debate. But logical fallacies do a lot of damage. They threaten to undermine shared truths and advance unwarranted conclusions that rest on flawed foundations. In an age of fake news, they help fake news to proliferate.

This is your chance to spot the devil in the details. Learn how not to be deceived, because, at the risk of sounding like an alarmist, there are people out there trying to deceive you. If the purpose of debate is to illuminate the truth at the center of a discussion, logical fallacies are the smoke and shadows that obscure this truth, keeping the participants on every side of the issue from seeing clearly.

Learn these logical fallacies. Call them out when you see them. Avoid committing them yourself. This is one of the most powerful actions you can take toward preserving and advancing truth.

Not convinced? Check out our 5 Reasons You Should Take Logic Your First Year in College.

Otherwise, read on and find out which logical fallacies you’re most likely to encounter in a debate...

Common Informal Fallacies

1.Ad Hominem

An abbreviated phrase meaning “to the person,” argumentum ad hominem refers to an argument which relies on an attack directed at the speaker rather than the substance of the speaker’s argument. This rhetorical strategy is often fallacious in nature, employing an approach designed to discredit the character, substance or motive of a person in lieu of deconstructing the person’s claims.

Example 1

• Speaker 1: I think the idea of a moral law requires the existence of a lawgiver (i.e. God).
• Speaker 2: Of course you would say that. You’re a Christian. Why should we listen to you?

Example 2:

• Speaker 1: I think marijuana should be legalized. It would be better for the country if we didn’t have this drug war.
• Speaker 2: Of course you think that. You’re a pothead.

Example 3:

• Speaker 1: No fault divorce has proven to be detrimental to society and the family.
• Speaker 2: You didn’t seem to think that when you got divorced.

Example 4:

• Speaker 1: We should have single payer, government funded health care. That would be the best solution to the health care crisis in our country.
• Speaker 2: You voted for Bernie Sanders. You’re probably a communist.

Fun Fact: An ad hominem observation is not always fallacious. If the qualities attributed to the speaker are provable and relevant to the argument, an ad hominem observation may be a useful point of strategy. For instance:

• Speaker A: Private health insurance is the only way to ensure the equal distribution of resources to the public.
• Speaker B: As a former CEO of a private health insurance company who was convicted for falsifying performance reports, you can’t be trusted on this issue.

2.Appeal to Authority

The argumentum ad verecundiam, sometimes also called an “argument from authority,” describes an argument in which a speaker claims that their view is endorsed by a relevant authority figure. This claim of endorsement is presented as a sufficient argument unto itself, relieving the speaker of presenting any additional evidence to further their case. An alternate form of this fallacy is sometimes called the appeal to false or unqualified authority. In this case, the speaker might cite an individual with some measure of clout, but generally in an area outside the subject of the given argument. For instance, one might fallaciously cite a medical doctor’s opinion about politics simply because she is a very smart doctor.

Example 1:

• My philosophy professor believes in ghosts and goes to séances. She’s an intelligent, educated, person, so ghosts must be real, and spiritualism must be true.

Example 2:

• My minister says the Covid vaccine will cause genetic mutations. He has a college degree, and is a holy man, so he must be right.

Example 3:

• Aristotle thought women were inferior to men. Aristotle is one of the smartest men who ever lived, so he must be right about this.

Fun Fact: If both parties in a debate agree that the cited individual is a relevant authority figure, and that the facts stated in reference to this figure are accurately attributed, this appeal may not be fallacious. For this reason, there is some debate about whether or not the appeal to authority is always fallacious. However, in contexts such as science, where authority must be challenged in order for new findings to be yielded, any such appeal that comes without the support of empirical evidence should be dismissed as fallacious.

3.Appeal to Ignorance

Argumentum ad ignorantiam, also sometimes referred to as an “argument from ignorance,” occurs when a speaker presents an argument as fact simply because there is no readily available evidence to prove the contrary. This fallacy is based on a false dichotomy which posits that what we don’t know must not be true. This strategy incorrectly assumes that a lack of sufficient evidence is concrete proof that something can’t be true, a position which precludes the possibility that things may be unknown or even unknowable.

Example 1:

• No one has proven God exists, so He doesn’t.

Example 2:

• You can’t prove God doesn’t exist, so He does.

Example 3:

• We haven’t proven aliens didn’t create life on earth, so aliens created life on earth.

Example 4:

• We haven’t found life on other planets, so there’s no life on any other planet, anywhere.

Example 5:

• We haven’t found the ruins of Troy, so the city of Troy didn’t really exist.

Example 6:

• We haven’t found King David’s tomb, so King David didn’t really exist.

Fun Fact: Philosopher John Locke is sometimes credited with first coining the phrase in his 1690 text “On Reason.” Here, he explains that one way “men ordinarily use to drive others and force them to submit to their judgments, and receive their opinion in debate, is to require the adversary to admit what they allege as a proof, or to assign a better.”

4.Appeal to Pity

The argumentum ad misericordiam is a strategy in which one speaker appeals to the emotions of another by exploiting their feelings of guilt or pity. This strategy of debate seeks to validate one’s argument by playing on the sympathy or sensitivity of the other. The aim is to invoke an array of emotions that might cloud the individual’s ability to approach the argument in a rational way. It should also be noted though that the invocation of empathy is not by itself evidence that a fallacy has occurred. If we take, for instance, commercials which feature starving people in developing countries, the goal of invoking our pity is not to deceive but to connect real human emotion with a call to action. An appeal to any type of emotion is not by itself fallacious, but becomes fallacious when combined with a faulty premise.

Example 1:

• You should give me a promotion. I have a lot of debt and am behind on my rent.

Example 2:

• You can’t give me a C. I’ll lose my scholarship.

Example 3:

• I can’t take home a B in this course. My parents will be angry with me.

Example 4:

• If you don’t give me a passing grade, I won’t get accepted to medical school. That will break my grandmother’s heart.

Example 5:

• You should marry me. I know we’re not compatible, but I only have a year to live, and you’re my last chance.

Fun Fact: The appeal to sympathy is sometimes also referred to as the Galileo argument, so-named in honor of the Italian astronomer who lived out his final decade under house arrest for scientific claims that were deemed heretical by the Catholic Church. Presumably, what is meant by this attribution is that one’s sympathy for Galileo’s ordeal does not necessarily confer agreement with Galileo’s theories. There is no recorded instance in which the pioneering astronomer employed such a rhetorical strategy on his own behalf.

5.Appeal to Popular Opinion

The argumentum ad populum, also sometimes referred to as the common belief fallacy, refers to an instance in which a speaker asserts that something is true because many people believe it to be so. This is a fallacy in which the speaker, in lieu of providing evidence to support an argument, asserts that something is demonstrably true only because a majority of people believe it to be the case. Another form of this fallacy is called the bandwagon fallacy, so named for its implication that one should adopt a view or opinion (i.e. join the bandwagon) because so many others believe it to be so. One more variation, the appeal to elite status, suggests that you might want to share a view or position because it is held by an elite set of individuals. For instance, a well-known recruitment slogan “The few. The proud. The Marines.” both conferred elite status upon the Marines and in doing so, implied that you might want to join this select group.

Example 1:

• Most people think the world is flat, therefore it is flat.

Example 2:

• Most actors in Hollywood were against the war in Iraq, therefore the war in Iraq was wrong. (This is a subsection of ad populum: snob appeal. In this case, the opinion is outside the expertise of the people appealed to.)

Example 3:

• Most wealthy women wear Gucci, therefore Gucci items are beautiful, and worth the price. (Snob appeal: appeal to the elite.)

Example 4:

• Throughout history, most philosophers thought men were more rational than women, therefore this is true.

Example 5:

• Most people don’t think it’s wrong to eat meat, so it’s not.

Example 6:

• Most people believe in ghosts, so ghosts are real.

Example 7:

• Slavery is accepted by just about everyone in our society, so it’s ethical to keep slaves.

Fun Fact: If an argument is actually centered on matters of public or democratic interest, the appeal to popular opinion may be a logically sound strategy. For instance, if provable, you may argue that because 9 of 10 dentists recommend Crest toothpaste, your dentist is likely to view Crest as a superior brand of toothpaste. This would not be a fallacy.

6.Appeal to the Stone

The argumentum ad lapidem is a logical fallacy in which one speaker dismisses the argument of another as being outright absurd and patently untrue without presenting further evidence to support this dismissal. This constitutes a rhetorical effort to exploit a lack of readily available evidence to support an initial argument without necessarily presenting sufficient evidence to the contrary. By its very nature, Appeal to the Stone preempts further debate. It insulates itself against counter-argument by declining to present sufficient evidence to be rebutted. A fallacy relying on inductive reasoning, appeal to the stone is a particularly vulnerable fallacy in contexts where new evidence may eventually reveal itself.

Example 1:

• Speaker 1: Humans share a common ancestor with the chimpanzee.
• Speaker 2: No they don’t. Don’t be ridiculous.
• Speaker 1: Why am I ridiculous?
• Speaker 2: Evolution is absurd.
• Speaker 1: Why do you say that?
• Speaker 2: Well, it just obviously is. Look at apes, and then look at us. It’s just obviously an absurd theory.

Example 2:

• Speaker 1: Race is a social construct.
• Speaker 2: No, it isn’t. Don’t be absurd.
• Speaker 1: What’s absurd?
• Speaker 2: The idea that race is a social construct.
• Speaker 1: What’s absurd about it?
• Speaker 2: It just is.

Fun Fact: This fallacy is drawn from a pretty entertaining origin story. 18th century English writer Dr. Samuel Johnson and his future biographer, Scottish-born James Boswell , discussed a theory offered by Church of Ireland bishop, George Berkeley . Berkeley had claimed, through the concept of subjective idealism, that reality and material objects are dependent upon an individual’s perceptions. Both Johnson and Boswell were firm in their shared rejection of this idea. However, according to Boswell’s biography of Johnson, “I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, ‘I refute it thus.’”

7.Causal Fallacy

Also sometimes called the fallacy of the single cause, or causal reductionism, this is a logical fallacy in which the speaker presumes that because there is a single clear explanation for an effect, that this must be the only cause. This fallacy makes the incorrect and reductive assumption that one cause precludes that possibility of multiple causes. This is a false dilemma, one which requires the speaker to ignore the possibility of other overlapping explanations and to consequently draw an unwarranted connection between a perceived cause and effect.

Example 1:

• I go to my front porch every morning and yell, “May no tigers enter this house!” and for 20 years, not a single tiger has entered my house. My tiger prevention strategy clearly works. .

Example 2:

• It’s cold on a summer day. Global warming is a hoax.

Example 3:

• I’ve never had the flu because I take my vitamins everyday.

Fun Fact: In essence, causal fallacy is the technical term for the exceedingly common phenomenon of “jumping to conclusions.” This is simply worth noting because it is, in many ways, a natural human behavior to which we are all predisposed at one time or another—as you await the results of a medical test; ponder the whereabouts of your missing wallet; or question the reasons somebody hasn’t texted you back even though you can clearly see that the message was delivered. In other words, uncertainty and human emotion make us all vulnerable to the occasional logical fallacy.

8.Circular Argument

Circulus in probando in Latin, this logical fallacy occurs when the premise of an argument is dependent upon acceptance of the conclusion, and the conclusion is dependent upon acceptance of the argument. In other words, both the argument and the conclusion are left wanting further proof. In circular reasoning, the originating premise lacks grounding in independent evidence, and therefore brings to the discussion no further proof to support the conclusion.

Example 1:

• Speaker 1: You should trust the Bible because it’s the Word of God.
• Speaker 2: How do you know it’s the Word of God?
• Speaker 1: Because God tells us it is.
• Speaker 2: Where does God tell us this?
• Speaker 1: Right here, in the Bible.

Example 2:

• Speaker 1: Jesus was not really crucified.
• Speaker 2: How do I know that’s true?
• Speaker 1: Because the Koran says so.
• Speaker 2: How do I know the Koran is correct?
• Speaker 1: Because the Koran is the Word of God, and everything it says is true.
• Speaker 2: How do I know that’s true?
• Speaker 1: Because God tells us so, here in the Koran.

Fun Fact: Circular reasoning forms the basis for the famous literary phrase “Catch-22,” which is drawn from the Joseph Heller novel of the same name. According to the satirical novel, the military maintains a policy of discharging soldiers who can demonstrate insanity. However, the military also recognizes that any sane person would desire a discharge to avoid the horrors of war. Therefore, any person seeking a discharge on the grounds of insanity is logically too sane to be eligible for discharge. This absurd contradiction is what is known, according to the author, as a “Catch-22.”

9.Equivocation

Sometimes called the Motte-and-Bailey fallacy, this is a logical fallacy in which a speaker blurs the line between two distinct positions which have some overlapping qualities. By blurring this line, it becomes possible to create an association between one position which is modest (Motte), and therefore easily defended, and a position which is likely to be more extreme (Bailey), and which is therefore more difficult to defend. By equating these positions, the speaker is presenting a false equivalence, thus forcing the other speaker to move to the defense of a position which is more difficult to defend.

Example 1:

• Speaker 1: Did you torture the prisoner?
• Speaker 2: No, we just held him under water for a while, and then did a mock hanging.

Example 2:

• According to the Supreme Court, we have a right to abortion. Therefore, it is right to have an abortion. (Legal right v. morally correct)

Example 3:

• A slight variation on equivocation occurs when common terms are used in an argument but with different meanings. For instance:
• Speaker 1: We are using thousands of people, who are going door to door to help us spread the word about social injustice and the need for change.
• Speaker: Well then, I can’t be a part of this because I was always been taught that it’s wrong to use people.

Example 4:

• Motte & Bailey Fallacy (Subset of equivocation)
• Motte (easily defensible): Different cultures and individuals have different opinions on morality.
• Bailey (more controversial/radical): Morality is completely subjective, and only a matter of opinion. There is no objective morality.

Fun Fact: The term Motte-and-Bailey was coined by philosopher Nicholas Shackell , who described the phrase as a reference to medieval castle defense systems, explaining that “A Motte and Bailey castle is a medieval system of defence in which a stone tower on a mound (the Motte) is surrounded by an area of land (the Bailey) which in turn is encompassed by some sort of a barrier such as a ditch...the Bailey, represents a philosophical doctrine or position with similar properties: desirable to its proponent but only lightly defensible. The Motte is the defensible but undesired position to which one retreats when hard pressed.”

10.Fallacy of Sunk Costs

The sunk cost fallacy proceeds from the faulty logic that the expenditure of past resources justifies the continued expenditure of resources. This fallacy contradicts rational choice theory, which holds that in economics, the only rational decisions are those which are made based on future expenses, rather than past expenses. In a broader sense, this fallacy can apply to a wide range of scenarios including the sunk cost of having remained in an unhappy relationship, having engaged in a failed war, or having dedicated years to an unsatisfying job. In each case, one might commit a fallacy by determining that past commitment to any of these scenarios necessitates a continuation of the status quo.

Example 1:

• Our marriage is terrible, but we’ve been together so long we might as well stay together. If we get divorced, I will have wasted 30 years.

Example 2:

• I hate this book. It isn’t very good. I’ve started reading it, though, so I should finish it. If I don’t finish it, I will have wasted 8 hours of my life.

Example 3:

• Our country has been in this war for 10 years. We’re not winning, but we continue to invest time, money, and soldiers in it because of past expenditures.

Fun Fact: A “sunk cost” is essentially the opposite of “cutting one’s losses.” For instance, in a hand of poker, a player may determine that while he is likely to lose based on his cards, he has already spent too much money on the hand to fold. This is a demonstration of the sunk cost fallacy. By contrast, the same player may recognize that while he has already spent a sum of money on this losing hand, he can still fold and hold on to his remaining funds. This is called cutting one’s losses.

11.False Dilemma

Also sometimes referred to as a “false dichotomy,” this is a fallacy in which one incorrectly places limitations on one’s possible options in a given scenario. This fallacy rests on the false premise that one is faced with a binary choice when it’s possible that multiple options are available. In essence, this occurs when one reduces the array of available options and alternatives to a simplified either-or condition.

Example 1:

• If you aren’t a capitalist, you must be a communist.

Example 2:

• Either God created the world or evolution is true.

Example 3:

• Speaker 1: I’m against the war.
• Speaker 2: You must hate our troops.

Example 4:

• You can either support our police or Black Lives Matter.

Fun Fact: The false dichotomy conflates “contraries” with “contradictories.” With contradictories, it is true that one or the other must be true. For instance, if we say somebody is alive, it means they must not be dead, and vice versa. By contrast, contraries are statements in which, at most, one such statement must be true, but in which it is also possible that neither statement is true. For instance, if we say that somebody “is not here,” we can’t definitively conclude that the person must be at home. It’s possible that the person is at home, at the supermarket, or aboard the international space station. We don’t know. From the statement, all we can conclude is that the person is not here. The false dichotomy overlooks the full array of possibilities.

12.Genetic Fallacy

Also sometimes referred to as the fallacy of origins, this is a fallacy which presumes that an argument holds no merit simply because of its source. In this instance, the history or origin of the source is used to dismiss an argument, in lieu of using actual rhetoric to address the substance of the argument.

Example 1:

• Speaker 1: That scientist gave a report last week on the relationship between fossil fuel and global warming. He says burning fossil fuels contributes to global warming.
• Speaker 2: He belongs to the Sierra Club and owns stock in a solar energy company. What he says cannot be true.

Example 2:

• Primitive people believed in gods to explain natural phenomena. We have science, and are not primitive anymore. Therefore, there is no God.

Example 3:

• Speaker 1: Dr. Singh says meat eating is bad for the environment.
• Speaker 2: He’s a Sikh. They don’t eat meat. Of course he would say that. He can’t be telling the truth.

Fun Fact: In one of the earliest recorded cases of usage, author Mortimer J. Adler characterized this fallacy as “the substitution of psychology for logic.”

13.Hasty Generalization

Also sometimes called a faulty generalization, this is a form of argument which arrives at a conclusion about numerous instances of a phenomenon based on evidence which is limited to only one or a few instances of said phenomenon. This denotes that one might attempt to generalize the explanation for an occurrence based on an unreliably small sample set.

Example 1:

• My grandmother smoked for 80 years and died at 100. Obviously, smoking isn’t harmful.

Example 2:

• I know five people from Kentucky. They are all racists. Therefore, Kentuckians are racist.

Example 3:

• My neighbor’s child was kidnapped while playing alone in her yard. My city must be a dangerous place for children.

Example 4:

• I know four poor families. They are lazy drug addicts. Therefore, all poor people are lazy drug addicts.

Fun Fact: The hasty or faulty generalization is the fallacy which is most at play when we apply stereotypes to full demographic groups based on anecdotal evidence or limited interaction with only select representation from that group. For instance, a person who owned a pet cat with a bad temper might make the stereotypical generalization that all cats have bad tempers.

14.Loaded Question Fallacy

A loaded question is one in which the speaker has employed rhetorical manipulation in order to limit the possible array of answers that another speaker can rationally provide. The fallacy is couched in the phrasing of such a question, which presupposes certain facts that may not be true or proven, within the content of the question. The fallacy occurs when that question is underscored by a presupposition which is not agreed upon by the person to whom the question is posed.

Example 1:

• Have you stopped beating your wife?

Example 2:

• Why did you steal my keys?

Example 3:

• Are you one of those stupid religious people that reject science?

Fun Fact: This form of fallacy is distinct from “begging the question,” which presumes the conclusion before the question is answered. By contrast, this strategy traps the respondent into admitting a fact which is implied by the question. Simply by virtue of answering the question, the respondent has unwittingly conceded the point.

15.Post Hoc Fallacy

In full Latin phrasing, Post hoc ergo propter hoc means “after this, therefore because of this.” Instances of this fallacy occur when one incorrectly attributes a cause and effect relationship between two phenomena in the absence of proof that one causes the other. The flaw in this strategy is that it draws a singular relationship between a premise and a conclusion without considering an array of variables that might disqualify the possibility of such a relationship.

Example 1:

• Every time we sacrifice virgins, it rains. Therefore, sacrificing virgins causes it to rain.

Example 2:

• Violence among teens has risen the last five years. Video game playing among teens has also risen the last five years. Therefore, playing video games causes teens to be violent.

Example 3:

• Every time I wear this necklace, I pass my exams. Therefore, wearing this necklace causes me to pass my exams.

Example 4:

• Every person who has ever drunk water has died. Therefore, drinking water causes death.

Fun Fact: A famous phrase often used as a counterpoint to the Post Hoc fallacy is that “correlation does not equal causation.” This denotes that just because two phenomena sometimes, or even frequently, appear in connection with one another does not mean that one causes the other.

16.Red Herring Fallacy

The red herring fallacy refers to an instance in which one speaker attempts to divert the attention of another speaker from the primary argument by offering a point which may be true, but which does not actually further the substance of a counterargument. So named for the implication that the odoriferous fish in question might “throw one off the scent” of the actual argument itself, the red herring will typically support a conclusion with a fact which does not actually provide substantive support.

Example 1:

• Child: This fish tastes funny. I don’t want to eat this.
• Parent: There are children starving in Africa. Eat your dinner.

Example 2:

• Speaker 1: I think it’s terrible that a game hunter killed Cecil the lion.
• Speaker 2: What about all the babies that are killed every day by abortion?

Example 3:

• Speaker 1: I really think we need to do something about the rising levels of poverty and homelessness in our country.
• Speaker 2: Why are you worried about poverty? Look how many children we abort every day.

Fun Fact: While the red herring can take the form of a logical fallacy, it is also a familiar literary and cinematic device which can be employed to misdirect the attention of the reader or viewer. This is a commonly employed tactic in mysteries, suspense thrillers, and other narratives that conclude with unexpected plot twists. For instance, in a murder mystery, the author might offer a number of clues implying that an innocent character is the killer while the actual killer hides in plain sight.

17.Slippery Slope Fallacy

Sometimes also called the continuum fallacy, this fallacy occurs when a speaker claims that a single step taken in a particular direction will inevitably lead to a series of subsequent and unintended events. This argument is used to draw a series of unforeseen and unprovable conclusions based on a single provable premise. The flaw in the slippery slope argument is that it typically forecasts an extreme range of likely subsequent events, thereby excluding the possibility that a series of more moderate events might play out instead.

Example 1:

• You smoke pot? If you keep doing that, you’ll be a heroin addict within two years.

Example 2:

• If we legalize pot, the next thing you know people will want to legalize meth and heroin.

Fun Fact: In the literary context, “slippery slope” is sometimes referred to as “the camel’s nose.” This refers to a metaphor taken from an allegory published by Geoffrey Nunberg in 1858, which tells the story of a miller who allows a camel to stick its nose through the doorway of his bedroom. Bit by bit, the camel moves other body parts into the room until he is entirely inside. Once this occurs, the camel refuses to leave.

18.Strawman Argument

The strawman fallacy occurs when a speaker appears to refute the argument of another speaker by replacing that argument with a similar but far flimsier premise. In essence, the speaker is “setting up a straw man” which can then be easily knocked down by a counterargument. The flaw in this rhetorical approach is that it fails to actually engage the original argument, in essence changing the subject so as to face a more manageable argument.

Example 1:

• Speaker 1: I think we should lower the age of sexual consent to 16.
• Speaker 2: 16 year olds are children. So, you think it’s OK for children to have sex? No, we shouldn’t lower the age of consent.

Example 2:

• Speaker 1: I think we should have single payer, universal, health care.
• Speaker 2: Communist countries tried that. We don’t want America to be a communist country. We shouldn’t have single payer health care.

Example 3:

• Speaker 1: I think we should have an expanded social safety net for the poor in our country.
• Speaker 2: So, you think we should just throw money at lazy people who don’t want to work and think they are entitled to be kept up by other people, right?

Fun Fact: In the U.K., the strawman argument is also sometimes referred to as “Aunt Sally,” so named for a pub game in which competitors will hurl sticks at a “skittle” balanced atop a post. The individual who knocks this precariously balanced object from its post is the winner.

19.Tu Quoque

Tu quoque, which translates to “you also,” is a fallacy in which one speaker discredits another by attacking their behavior as being inconsistent with their argument. This is a specious attack line because it seizes on certain characteristics presented by the speaker rather than on the merits of the speaker’s actual argument. Similar to ad hominem in that it resorts to a personal line of attack rather than a rhetorical argument, the primary distinction is that this personal attack is framed as having a direct connection to the argument itself. This framing is not designed to disqualify the speaker for who they are (as with ad hominem) but for how they act, and consequently, how this action appears to diverge from the premise of the speaker’s argument.

Example 1:

• Speaker 1: No fault divorce is really harmful to the family and the larger society.
• Speaker 2: Well, you must not really think that since you’re divorced yourself.

Example 2:

• Parent: I really don’t want you to smoke pot. It’s still illegal, and could get you into trouble.
• Child: Didn’t you smoke pot when you were my age? You must not think it’s a big deal.

Example 3:

• Speaker 1 (Democrat): “Donald Trump is a known adulterer. It reflects badly on his character, and suggests he might not be trustworthy.”
• Speaker 2 (Republican): “What about Bill Clinton? You didn’t seem to care when he cheated.”

Fun Fact: The high level of polarization in today’s American political discourse leads frequently to a form of the tu quoque fallacy referred to as “whataboutism.” This form of the fallacy occurs when one speaker, in lieu of responding directly to an argument, accuses another speaker of taking a hypocritical position. Take, for instance, a debate over gun control between a Republican and a Democrat:

• Democrat: Republicans support fewer regulations on gun ownership, which leads to more gun-related deaths in America.
• Republican: Well what about how Democrats support drug legalization, which leads to more drug-related deaths in America?

Common Formal Fallacies

20.Affirming the Consequent

Sometimes also referred to as a converse error, this is a fallacy which occurs when one assumes that, because a conditional statement is true, then the converse of that statement must also be true. In such instances, this assumption is based on a failure to consider other possible antecedents which might also be used to offer true conditional statements. In other words, the speaker has failed to consider the full range of possible conditions for that which is consequent.

Example 1:

• If Hunter was human, he would be mortal. Hunter is mortal. Therefore, Hunter is a human.(Hunter may actually be my cat.)

Example 2:

• If it was raining outside, it would be dark. It’s dark outside, so it must be raining. (It might be 10PM.)

Example 3:

• If I’m psychic, I will be able to see dead people. I see dead people, therefore I’m psychic. (I might actually just be insane.)

21.Affirming the Disjunct

In the case of Affirming the Disjunct, also sometimes referred to as the false exclusionary disjunct, it is incorrectly presumed that an “or” condition excludes the possibility that “either/or” could be true. In other words, when a speaker makes a statement indicating “A or B,” the fallacy occurs when the responding speaker assumes “A, therefore, not B.” This is a fallacy of equivocation in which one assumes that because one disjunct is true, the other must be untrue.

Example 1:

• Gus is Christian or Gus is politically liberal.
• Gus is a Christian.
• Therefore, Gus is not politically liberal.

Example 2:

• Either God created the world or evolution happened.
• Evolution happened.
• Therefore, God did not create the world.

Fun Fact: Whereas Affirming the Disjunct is a logical fallacy, it should not be conflated with the disjunctive syllogism which is actually a valid form of argument. An example of an accurate disjunctive syllogism states the following:

• Bruce is American, or he is not from New Jersey.
• Bruce is not American, therefore, he is not from New Jersey.

This is a valid form of inference.

22.Appeal to Probability

The possibiliter ergo probabiliten refers to a fallacy in which one conflates possibility with probability, or in which one conflates probability with certainty. At the heart of this inductive fallacy is the error in presuming that because there is evidence that a thing is possible, one can take for granted either its probability or its certainty.

Example 1:

• It is possible aliens built the pyramids. Therefore, aliens built the pyramids.

Example 2:

• It is possible to fake the moon landing through special effects. Therefore, the moon landing was a fake using special effects.

Example 3:

• It’s possible to pass the class without attending regularly. Therefore, you will pass even if you don’t attend regularly.

Fun Fact: Murphy’s Law famously states that anything which can go wrong, will go wrong. This is a playful and purposeful manifestation of the Appeal to Probability Fallacy.

23.Argument From Fallacy

Also redundantly known as the fallacy fallacy, this fallacy occurs when one speaker identifies a fallacy in the argument of another and uses it in order to assert that the conclusion must be false. This fallacy incorrectly assesses that a fallacy within the argument of another necessarily precludes the possibility that the argument’s conclusion is correct.

Example 1:

• Speaker 1: If Hunter was human, he would be mortal. Hunter is mortal. Therefore, Hunter is a human.
• Speaker 2: You just committed the fallacy of affirming the consequent. Therefore, Hunter is not a human.

Example 2:

• Speaker 1: Single payer health care would be the fairest and most efficient way of giving medical care to our citizens.
• Speaker 2: You must be a communist.
• Speaker 1: You just committed the ad hominem fallacy. Therefore, I’m not a communist.

Fun Fact: This fallacy is a special form of the formal “Denying the Antecedent” fallacy. (See below.)

24.Conjunction Fallacy

In a conjunction fallacy, one assumes that a set of specific and combined conditions is likelier to be true than a single condition, without concrete evidence that either is true. In this instance, the specific set of conditions may appear to be more true because it seems to represent certain facts that seem likely to connect with the premise. However, because these conditions are more specific and because these conditions combine multiple factors which must all be true in order for the entire statement to be true, it is mathematically less likely that the statement is true than would be a simpler proposition.

Classic Example: The Linda Problem

Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.

Which is more probable?

• 1. Linda is a bank teller.
• 2. Linda is a bank teller and is active in the feminist movement.

If you chose #2, you have committed the conjunction fallacy. The probability of them both being true is less than or equal to the probability of only one being true. We do not know, in fact, whether either of them is true.

Fun Fact: This fallacy is sometimes called the “Linda problem,” following from the first known example supplied by psychologists Amos Tversky and Daniel Kahneman .

25.Denying the Antecedent

Sometimes also referred to as the fallacy of the inverse, denying the antecedent occurs when one deduces that because a valid premise leads to a valid conclusion, that the inverse can’t be true. In this case, the fallacy occurs when an individual presumes that because a premise and conclusion are true, the opposite of that premise must inherently mean that the conclusion is not true. In other words, one may make the valid statement that “If A, then B.” It would be a fallacy to determine that “If not A, then not B.”

Example 1:

• If you live in Kentucky, you love horses.
• You don’t live in Kentucky.
• Therefore, you don’t love horses.

Example 2:

• If you’re a hippie, you smoke weed.
• You are not a hippie.
• Therefore, you don’t smoke weed.

Example 3:

• If you are a communist, you believe in socialized medicine.
• You are not a communist.
• Therefore, you do not believe in socialized medicine.

Fun Fact: An argument based on denying the antecedent may actually be valid if the biconditional terminology is added to indicate “if and only if.” For instance:

• If and only if tomatoes grow on trees, then tomatoes must be fruit.
• Tomatoes don’t grow on trees. Therefore, tomatoes are not fruit.

26.Denying a Conjunct

This fallacy occurs under the condition that two premises cannot both be true at the same time. Under said condition, it is incorrect to presume that because A is not true, then B must be true. The primary flaw in this presumption is the preclusion of the possibility that neither premise is true.

Example 1:

• It isn’t both sunny and raining.
• It isn’t sunny.
• Therefore, it’s raining.

Example 2:

• Teena is not both a hippie and a communist.
• Teena is not a hippie.
• Therefore, Teena is a communist.

Example 3:

• I can’t be a pothead and get a job at the factory.
• I’m not a pothead.
• Therefore, I can get a job at the factory.

Fun Fact: The conclusion of the sequence need not be false in order for Denying a Conjunct to be a logical fallacy. In the example above, it is possible that the speaker could get a job at a factory. But we can’t presume that this is the case simply because the speaker isn’t a pothead. It’s possible, for instance, that regardless of whether or not the speaker smokes pot, this individual lacks the training to be hired as a factory worker.

27.Existential Fallacy

Also sometimes called existential instantiation, this fallacy occurs when one makes an argument about a category without first presenting any proof that such a category exists. In other words, it is not logical to attribute characteristics to that which doesn’t exist. Therefore, an argument which simply assumes existence while attributing such characteristics is based on an unproven premise.

Example 1:

• All sea creatures live in the water.
• All mermaids are sea creatures.
• Therefore, some mermaids live in the water.

(The problem here is that you may have a category of things that actually do not exist. What if there are no mermaids?)

Example 2:

• All cats are aliens. All aliens are dangerous. Therefore, some cats are dangerous. (What if cats didn’t exist?)

Fun Fact: “All trespassers will be prosecuted” is an oft-used existential fallacy, one which fallaciously assumes without evidence that there are trespassers even though we can’t presume the existence of trespassers based on the information provided in the statement. This fallacy can be readily corrected when one adds the condition “if such-and-such exists.” Thus, while it would not fit so elegantly on a posted sign, it would not be a fallacy to say, “If trespassers are found on my property, they will be prosecuted.”

28.Fallacy of the Undistributed Middle

Referred to in Latin as non distributio medii, this fallacy is considered a syllogistic fallacy. A syllogism is a kind of argument which occurs when two propositions are asserted to be true and, therefore, may allow one to arrive at a particular conclusion through deductive reasoning. A syllogistic fallacy occurs when there is a logical flaw in either or both propositions which prevents one from deducing this conclusion. With the undistributed middle, a fallacy occurs when a “middle term,” which is needed to reach the desired conclusion, is not included in either of two propositions.

Example 1:

• All students carry backpacks.—(Z is B)
• My grandfather carries a backpack.—(Y is B
• Therefore, my grandfather is a student.—(Y is Z)

A valid form of this argument would be as follows:

• All students carry backpacks.—(Y is B)
• My grandfather is a student.—(Z is Y)
• Therefore, my grandfather carries a backpack.—(Z is B)

Fun Fact: Technically, all fallacies of the Undistributed Middle are actually fallacies of either Affirming the Consequent or Denying the Antecedent. The primary distinction is that the fallacy of the undistributed middle may actually be corrected by distributing the middle, as it were. For instance, the following would be considered a fallacy:

• All billionaires are astronauts.
• Jeff Bezos is an astronaut.
• Therefore, Jeff Bezos is a billionaire.

However, we can correct the fallacy above by presenting the argument as follows:

• All billionaires are astronauts.
• Jeff Bezos is an astronaut.
• Everyone who is an astronaut is a billionaire.
• Therefore, Jeff Bezos is a billionaire.

By adding the third statement in this sequence, we have provided the “middle term” which may then be distributed to the conclusion.

29.Masked-man Fallacy

Sometimes also called the epistemic fallacy, this occurs when one assumes that because one object has a certain property, and the other does not have this property, that they cannot be the same thing. This is a fallacious assumption because it concludes that one’s knowledge of the object is equivalent to the object itself. It erroneously precludes the possibility that the object in question has some properties which are unknown to the subject.

Example 1:

• I know who my father is.
• I don’t know who the masked man is.
• Therefore, the masked man cannot be my father.

Example 2:

• I know who my husband is.
• I do not know who the robber is.
• Therefore, my husband cannot be the robber.

Fun Fact: The Masked-man Fallacy is actually an illicit use of Leibniz’s law. According to the law proposed by the German logician, if A is the same as B, then A and B share the same properties and are therefore indiscernible from one another.

30.Non-Sequitur Fallacy

Technically, a non sequitur is any invalid argument where a given premise does not logically support the given conclusion. In this way, the phrase non sequitur is practically synonymous with the word fallacy. However, in the context of a discussion on formal fallacies, a non-sequitur is a statement in which the premise has no apparent relationship with the conclusion, and therefore cannot be used to ascertain that this conclusion is true.

Example 1:

• I dated a lawyer. All he talked about was work. Lawyers are boring.

Example 2:

• My last boyfriend was really mean to me. All men are abusive.

Example 3:

• People like to walk on the beach. Beaches have sand. We should put sand on the floor in our living room.

Fun Fact: A non sequitur is also a commonly used device in literature and especially comedy. Here, by pairing an expected premise with an unexpected and technically fallacious conclusion, a comedian may offer an absurd and humorous observation. Take, for example, this observation from stand-up comedian Steven Wright:

• “I saw a sign: ‘Rest Area 25 Miles.’ That’s pretty big. Some people must be really tired.”

If you need to prepare for a debate, but feel clueless about how to even take notes in class, check out our guide to effective note-taking.

If you’re fascinated by the mechanics of logic, you may be naturally predisposed to the philosophy discipline. The list above really only scratches the surface on deeply intertwined subjects like logic, reason, and rhetoric. Check out these resources and rankings when you’re ready to plunge beneath this surface:

• How to Major in Philosophy
• What Can I do With a Master’s in Philosophy
• Five Reasons You Should Take Logic in Your First Year of College
• Top Influential Philosophers Today
• 25 Most Influential Philosophy Books

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