Fallacies are generally split into two types: formal and informal. Under these two categories, we have a whole range of specific fallacies, which I’ll be defining in this article as ‘sub-types’.
The two main forms of logical fallacy are:
- Formal Fallacy: A formal fallacy is untrue because of the form or structure of the argument, but not necessarily the content or context. In other words, the relationship between the premise and conclusion lacks logic.
- Informal Fallacy: An informal fallacy is untrue because of the content or context of the argument, even if it is logical in its form. For example, the premise itself may be irrelevant or a misrepresentation of the truth.
Types of Fallacy
1. Informal Fallacies
Informal fallacies refer to unsound arguments that fall short as a result of their content or context.
Below are several sub-types that can be considered informal fallacies.
1. Ad Hominem
Ad hominem means ‘to the man’. It is an argument that attacks the person rather than the quality of their argument. I once fell foul of this with my elderly aunt while arguing about bitcoin. She said to me “I don’t like bitcoin because old people can’t understand it.” I replied “You just don’t like bitcoin because you don’t understand it.” Similarly, I notice a lot in politics that people won’t debate over Joe Biden’s policies, but rather, attack him for his age. This fails to address the argument, and instead, attacks the man.
2. Strawman Fallacy
This occurs when you misrepresent your opponent’s argument in order to make it easier to attack. For example, a mayor wants to raise taxes by 2% so his opponents re-frame this as a “communist government takeover”, turning the argument into something far worse than it truly is, in bad faith, to make it easer to attack and scare voters.
3. Appeal to Authority
This occurs when you using an authority as evidence in your argument, despite the fact that the authority isn’t even an authority on the topic at hand. For example, you might start taking a food supplement because billionaire tech investor Mark Cuban told you to. He’s an expert in business and technology, and yet you’re trying to invoke his expertise in relation to an issue of healthcare!
4. Bandwagon (Ad Populum)
The ad populum fallacy occurs when you use widespread acceptance (e.g. the majority opinion) about a topic as a rationale for its truthfulness. For example, 99% of people in my country are Muslims, and therefore, Islam is correct. This fails to provide a logical or independently valid defense of the position, but rather hides behind majority opinion on the matter.
5. False Dichotomy Fallacy
This occurs in situations where only two options are presented in service of a black-and-white argument, when there are more that could be considered. For example, a politician might say “you can either save the environment or heat your home,” neglecting other options, such as more efficient and environmentally friendly heating systems.
6. Post Hoc Ergo Propter Hoc
This fallacy assumes a cause and effect relationship where one doesn’t necessarily exist. For example, a tennis player eats chicken before a game, and he wins the game. From then on, he decides to always eat chicken before his games because it seems to cause him to win.
7. Circular Argument (Petitio Principii)
This refers to situations where you begin the argument with the conclusion, so you can reinforce your argument by referring back to your first statement. This may occur if you argued that God said in the bible that the bible is always right, so therefore the bible is always right, because God said so in the bible.
8. Hasty Generalization
A hasy generalization refers to situations where you come to generalized conclusions from a specific instance or dataset that is too small. For example, you might say that all men are smart because your dad is smart and he’s a man. To avoid this, we should look at statistically relevant data that reflect general demographic trends.
9. Red Herring Fallacy
A red herring fallacy occurs when someone distracts from the argument or otherwise distorts it by bringing in irrelevant information. For example, this might occur when a husband and wife are arguing because the husband didn’t do the dishes, and he retorts that two years ago he made her a coffee, which somehow should get him off the hook for not doing the dishes tonight.
10. Slippery Slope Fallacy
This refers to the argument that one thing will inevitably lead to another, when there is not hard evidence that this will be the case. For example, you might argue “your daughter is going to become a hardened criminal because she tends to steal her brother’s french fries when he isn’t looking.” The fact she steals her french fries is highly unlikely to mean she will end up in a life of crime – this is a slippery slope.
11. No True Scotsman
This happens when you redefine the criteria of a category to exclude counterexamples. The name comes from the idea that a Scotsman was a thief, but other Scotsmen said, well, he mustn’t be a Scotsman, because no Scotsman would be a thief. This helps in-groups maintain internal consistency, by rejecting any members who might function as counterexamples to their supposed superiority, purity or infalibility.
12. Appeal to Nature
Making the argument that because something is ‘natural’ it is therefore better, valid, justified, inevitable, good or ideal. This often occurs among alternative medicine adherents, who will automatically assume that natural is best, rather than engaging with a rational and scientific examination of the merits of various courses of action for an ailment.
13. Guilt by Association (Ad Hominem)
This refers to discrediting an argument for the reason that those who support the argument have bad character traits. This happens regularly in politics, for example, where an opposition party reflexively rejects a point made by the opponent based on the fact that it’s the opponent who proposed the point.
14. The Texas Sharpshooter
This happens when you find ways to make your argument accurate without using an objective methodology, such as by cherry-pick data clusters to suit your argument, or finding a pattern to fit a presumption. The metaphor here is of a Texan who shoots at a barn, then walks up to the barn and draws a target around where he hit the wall, and claiming he’s a perfect shot.
15. Burden of Proof Fallacy
Saying that the burden of proof lies not with the person making the claim, but with someone else to disprove. This often happens when Christians debate agnostics and skeptics, and insist that the skeptic must prove the non-existence of God, or else, the Christian God exists. The person making a claim to a theory – such as a claim to a specific religion – has the burden to proove it, not the person who is skeptical of the proposed religious theory.
Additional Informal Fallacies:
- Begging the Question
- False Equivalence
- Tu Quoque (“You also”)
- Genetic Fallacy
- Appeal to Ignorance (Ad Ignorantiam)
- Moving the Goalposts (Raising the Bar)
- Special Pleading
- The Fallacy Fallacy
- Appeal to Emotion (Pathos)
- Argument from Incredulity (Personal Incredulity)
- Composition Fallacy
- Appeal to Tradition (Argumentum ad Antiquitatem)
- Argumentum ad Novitatem (Appeal to the New)
2. Formal Fallacies
Formal fallacies fail in their internal logic: the premise doesn’t lead naturally or logically to the conclusion.
Below are several sub-types that can be considered formal fallacies.
1. Affirming the Consequent
Affirming the consequent involves taking a true conditional statement and reversing it, which creates an assumption that does not follow. For example, the true conditional statement “If you live in Seattle is broken, then you are American” cannot be inversed: “I am American, therefore, I live in Seattle.”
2. Denying the Antecedent
Denying the antecedent take the form: “If A then B. Not A, therefore not B”. Here, a person assumes that if the antecedent (the first part of an If-then statement) is false then the consequent (the second part, after “then”) is also necessarily false. However, we know this isn’t always the case. For example: “If your pet is a cat, then it has a tail. Your pet is not a cat. Therefore, it does not have a tail.” This is not necessarily true, because dogs also have tails.
3. Affirming a Disjunct
This takes the form: “A or B. A is true, therefore B is not true.” It assumes that ‘or’ signifies an exclusive binary, which is not always the case. It often leads to a false dilemma. For example, “To be in the country club, you must be rich or famous. Tom Hanks (who is in the club) is rich, therefore he is not famous.” Obviously, we’re overlooking the idea that Tom Hanks may be both rich and famous.
4. Denying a Conjunct
This takes the form: “Not both A and B. Not A, therefore not B.” For example, you may ask your friend on the phone, “Is it raining and snowing where you are?” The friend replies, “It’s not raining.” You assume that because it’s not raining, therefore, it is not snowing either. Here’s another example: “He is not both tall and strong. He is not tall, therefore, he is not strong.” Perhaps you have overlooked the fact he could be short and strong!
5. Illicit Major
This takes the form: “All A are B. All A are C. Therefore, all B are C.” For example, “All cats are mammals. All cats are felines. Therefore, all mammals are felines.” Of course, this is not true, because there are mammals who are not felines – such as canines! This fallacy assumes that B is A (a mammal is a cat), rather than the fact B merely has overlapping characteristics with A.
6. Illicit Minor
This fallacy takes the form: “All A are B. No C are B. Therefore, no C are A.” For example, “All dogs are mammals. No cats are dogs. Therefore, no cats are mammals.” This fallacy incorrectly concludes a universal negative from a universal affirmative and a particular negative. It is similar to Illicit major, in different form.
7. Fallacy of the Undistributed Middle
This fallacy takes the form: “All A are B. All C are B. Therefore, all A are C.” For example, “All dogs are mammals. All cats are mammals. Therefore, all dogs are cats.” This statement incorrectly assumes that two groups must be identical if they both share a common characteristic, and is more or less the same as illicit major and illicit minor, in a different format.
8. Fallacy of Exclusive Premises
This fallacy takes the form: “No A are B. No C are A. Therefore, no B are C.” For example, “No dogs are cats. No elephants are dogs. Therefore, no cats are elephants.” Despite stumbling upon a true point in this example, this fallacy has improperly drawn a conclusion from two negative premises.
9. Fallacy of Drawing an Affirmative Conclusion From a Negative Premise
This fallacy draws a positive conclusion from a negative premise. For instance, “No birds are dogs. All robins are birds. Therefore, some robins are dogs.” This conclusion is not logically warranted, because the premises offer no positive connection between robins and dogs.
10. Existential Fallacy
The existential fallacy assumes existence from a universal premise. While the argument would hold, if we use a non-existent entity (such as ‘unicorns’) in the premises, this fallacy can lead to a false assumption that the non-existent entity exists. For example, “All flying creatures have wings. Some unicorns fly. Therefore, some unicorns have wings.” This conclusion presupposes that unicorns exist, which is not indicated by the universal premise. While this sounds like it may be an informal fallacy (context is obviously missing), it is formal because it is the structure of the argument that leads people to presuppose the idea that unicorns exist.
Additional Formal Fallacies:
- Fallacy of the Four Terms
- Modal Fallacy
- Quantifier Shift Fallacy
- Masked Man Fallacy
- Necessity and Sufficiency Confusion
- Division Fallacy
- Composition Fallacy
- Definist Fallacy
- Fallacy of Hypothetical Syllogism
- Fallacy of Modal Logic
- Syllogistic Fallacy
While we have two main types of fallacies, as shown here, there are numerous other classifications of fallacies, within which we can find countless examples in all walks of life – from philosophy to politics to religious debates (from all sides!). By knowing our fallacies, we can be better debaters both because we can avoid using them ourselves (strengthening our own positions) and also identifying them in our opponents’ debate points.
Dr. Chris Drew is the founder of the Helpful Professor. He holds a PhD in education and has published over 20 articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education. [Image Descriptor: Photo of Chris]