Logical fallacies
Logical fallacies are flaws in reasoning that make an argument invalid. They can be either formal or informal.
- Formal Fallacies: These are fallacies that can be identified by examining the logical structure of an argument. They occur when the conclusion does not follow logically from the premises. An example is “affirming the consequent,” where someone claims that if one thing leads to another, then that second thing must necessarily mean the first thing occurred. For example: If it rains, the street will be wet. The street is wet. Therefore, it must have rained. (The street could also be wet for other reasons, such as a sprinkler system or a spilled bucket of water.)
- Informal Fallacies: These are errors in reasoning that involve the content of the argument, rather than its structure. They often involve misuse of language or some form of deception. There are many types of informal fallacies, including:
- Ad hominem: Attacking the character of a person making an argument rather than the argument itself.
- Appeal to authority: Claiming something is true because an unqualified or irrelevant ‘authority’ says it.
- Straw man: Misrepresenting an opponent’s argument in order to make it easier to attack.
- Red herring: Introducing an irrelevant point to divert attention from the subject of the argument.
- False cause (post hoc ergo propter hoc): Assuming that because B follows A, A must cause B.
Fallacies can be persuasive and are often used intentionally in politics, advertising and debate to sway the audience’s opinion. Understanding these logical fallacies can improve critical thinking skills and help in recognising when an argument is flawed.
YourLogicalFallacyIs.com
YourLogicalFallacyIs.com is a website which provides an overview of 24 of the most common types of logical fallacy with clear definitions and entertaining examples.
Each icon represents a fallacy and you simply hover over it to see more information.
Quizlet flashcard set
This set contains the definitions and examples from YourLogicalFallacyIs.com.
Ideas for teaching logical fallacies
- Lecture and discussion: Traditional lecture-style teaching can be a good starting point. Begin by explaining what logical fallacies are, their types and how they undermine arguments. After explaining each fallacy, engage students in discussions by asking them to provide their own examples or identify fallacies in given statements.
- Role play: Divide students into two groups and have each group prepare arguments for a debate that include logical fallacies. During the debate, the other group must identify the fallacies in real time.
- Case studies: Provide case studies of real-world scenarios where logical fallacies were used and had consequences, such as legal cases, political debates or business decisions. Discuss these as a class. See the section below on ChatGPT for ideas on how to generate examples.
- Games and quizzes: Create games or quizzes where students earn points for correctly identifying logical fallacies in given arguments. This can make learning more engaging and fun.
- Use visual aids: Create infographics or flashcards depicting various logical fallacies, or use existing resources available online. Visual aids can be especially helpful for visual learners. In addition to the fallacies Quizlet set which you can share with your students, you can download printable high-quality critical thinking tards, fallacies and biases wall posters for your classroom. (The download option is at the very bottom of the page.)
- Video Analysis: Use videos of debates, speeches or scenes from films or TV shows. Pause at critical moments to identify and discuss any logical fallacies present. Check out this playlist by a creative teacher of scenes from The Simpsons used to illustrate different logical fallacies. Skip the first part in which the narrator states which fallacy is at play and get your learners to formulate hypotheses about what the fallacy might be.
The goal is not for learners to memorise types of fallacies, but rather to understand why they are fallacies and how they weaken arguments. Methods that involve active participation, real-world examples and humour are often most effective. What’s more, learners need to understand that fallacies can have life-and-death consequences.
Teaching logical fallacies using ChatGPT
Here are two some examples of how ChatGPT can be used to teach logical fallacies.
If you want to teach inductively you can prompt ChatGPT to come up with stories or anecdotes that illustrate different logical fallacies and have learners identify what the faulty logic consists of, either before teaching logical fallacies or as a means of reviewing them. This could be done as a jigsaw activity.
Generating short anecdotes
The text below is the response generated by ChatGPT in response to the following prompt: Write ten anecdotes from everyday life, each of which illustrates a different logical fallacy.
- Ad hominem: During a community meeting about installing speed bumps, Tom says, “I don’t think we need speed bumps. The current speed limits are sufficient.” Lisa responds, “Well, you would say that, Tom, you’re a terrible driver.”
- Slippery slope: A parent tells their teenager, “If I let you stay out until midnight just once, the next thing I know, you’ll be coming home at dawn!”
- Appeal to authority: Alex says, “I read online that this celebrity uses this skincare product. It must be the best one available.”
- Straw man: During a debate on environmental regulations, Jane says, “I believe we need to balance regulations with economic impacts.” Mark responds, “So, you want to destroy jobs and ruin our economy for the sake of some birds and trees?”
- Circular argument: Sarah states, “I know my intuition is accurate because I always end up being right. And because I’m always right, I trust my intuition.”
- False dilemma: A coach tells his team, “Either you’re first, or you’re a loser. There’s no in-between.”
- Red herring: During a discussion about school budgets, a board member says, “We should focus on more important matters. Did you know the school soccer team hasn’t won a match this season?”
- Post hoc ergo propter hoc: Mary exclaims, “Every time I wash my car, it rains the next day. Washing my car must cause rain.”
- Hasty generalisation: After getting a flat tire on vacation, Bob grumbles, “The roads in this town are terrible. They must not care about road maintenance.”
- Begging the question: During an argument, Susan states, “You can’t give me a C on this paper. I’m an A student!”
Generating short stories
Similarly, we can get ChatGPT to generate short stories containing fallacies. The text below was generated in response to the following prompt:
Write a short story which contains example of four different logical fallacies. Do not mention the names of the fallacies in the actual story. Refer to them separately in a note at the end of the text.
Once upon a time, in the quaint town of Verityville, the topic of debate at the town meeting was whether to build a new playground. Leading the discussion was Mrs. Sanders, a renowned gardener in the town, who opposed the idea of a new playground.
Mrs. Sanders argued, “If we build a playground, then all kinds of rowdy kids will start coming into town. Before we know it, there will be graffiti everywhere and our peaceful town will become a hub of lawlessness.”
On the other side of the debate was Mr. Adams, the local barber. He responded, “Well, Mrs. Sanders, aren’t you the one who can’t even keep her petunias alive? How can we trust your judgement on what’s good for our town?”
Mr. Adams continued, “Furthermore, my uncle, who’s a famous town planner, always says that playgrounds add life to a town. So, building this playground will definitely improve our town’s atmosphere.”
At this point, Mrs. Higgins, the librarian, joined the discussion. She stated, “Surely you remember what happened in the neighbouring town of Serenityville. They decided against a playground and their town festival was poorly attended. We wouldn’t want that to happen here, would we?”
Note
- Mrs. Sanders uses a slippery slope fallacy, assuming one event will inevitably lead to a worst-case scenario.
- Mr. Adams commits an ad hominem fallacy, attacking Mrs. Sanders’ personal ability rather than her argument.
- Mr. Adams also uses an appeal to authority fallacy, assuming his uncle’s success as a town planner automatically validates his argument.
- Mrs. Higgins employs a post hoc ergo propter hoc fallacy, suggesting a cause and effect relationship between two unrelated events.
Comment: This task would might work better with learners generating their own stories with them tweaking the topic of the story to involve characters, themes, etc. that they find entertaining, which they then share and analyse.
Finding examples from history of the life-and-death consequences of bad logic
As suggested above, one way of approaching logical fallacies is to use case studies, that is, stories about events from the past in which fallacies played a decisive role.
The short texts below, like the one above, could easily be turned into a jigsaw task.
The following was generated by ChatGPT in reponse to this prompt: Give ten examples from history of fallacies that have had negative consequences for society. Do not include the name of the fallacy in the explanation but rather put in bold preceding the explanation. Write two sentences on each example.
Ad hominem: During the Middle Ages, people were often accused of witchcraft based on personal slurs and unfounded accusations rather than any solid evidence. This led to widespread hysteria and countless wrongful persecutions, severely disrupting society.
Slippery slope: In the 1950s, US Senator Joseph McCarthy exploited fears by suggesting that any trace of communism within the government would inevitably lead to a complete communist takeover. This propagated a sense of paranoia, leading to the infamous McCarthyist witch hunts that damaged numerous lives and careers.
Ad hominem and stereotyping: Adolf Hitler used harmful stereotypes and personal attacks to scapegoat and dehumanise Jewish people, blaming them for Germany’s economic woes. This directly led to the horrors of the Holocaust and had severe, lasting impacts on global society.
Cherry picking: For decades, tobacco companies highlighted data that downplayed the harmful effects of smoking, while ignoring the bulk of evidence showing a strong link between smoking and lung cancer. This manipulation contributed to the ongoing global health crisis related to smoking and tobacco use.
Appeal to ignorance and cherry picking: Some deny the overwhelming scientific consensus that human activities are driving climate change, instead focusing on minor uncertainties or areas of ongoing research. This denial has hampered global efforts to address and mitigate the catastrophic impacts of climate change.
Post hoc ergo propter hoc: A now-discredited study published in 1998 suggested a link between the MMR vaccine and autism. Despite its retraction and numerous subsequent studies debunking the link, vaccine hesitancy stemming from this study continues to affect public health initiatives worldwide.
Appeal to fear: Justifications for the 2003 invasion of Iraq were partially based on claims that Iraq possessed weapons of mass destruction posing a global threat. This misinformation led to a prolonged conflict with disastrous humanitarian and geopolitical consequences.
Hasty generalisation: During the colonial era, European powers often used generalisations to stereotype people in the regions they colonised as “primitive” or “savage,” justifying their colonisation and exploitation. This has had longstanding impacts on racial and cultural dynamics worldwide.
False cause: In the 19th century, proponents of phrenology falsely claimed that the shape and size of a person’s skull could determine their character and intelligence. This pseudoscience was used to rationalise social inequality and racial discrimination.
Stereotyping and hasty generalisation: In the United States, redlining policies relied on stereotypes and generalisations to categorise entire neighbourhoods with minority populations as “high risk” for loans. These policies led to systemic discrimination and significant socioeconomic disparities.