30 Common Logical Fallacies–A Study Starter

We help improve your debate skills with our rundown of the 30 most common logical fallacies. Not even sure what a logical fallacy is? Stick with us, we’ll cover the basics in this 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.

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:

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.

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.

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:

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.

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.

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.

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.

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.

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.

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.

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.