Read the notes, then try the practice. It adapts as you go.When you're ready.
Session Length
~17 min
Adaptive Checks
15 questions
Transfer Probes
8
Logical fallacies are errors in reasoning that undermine the logical validity of an argument. They occur when the structure of an argument fails to support its conclusion, even if the premises or the conclusion happen to be true. Understanding fallacies is essential for critical thinking because they appear constantly in everyday discourse -- in political debates, advertising, social media arguments, and even academic writing. Recognizing a fallacy does not mean the speaker's conclusion is automatically wrong; it means the reasoning used to reach that conclusion is flawed.
Fallacies are traditionally divided into two broad categories: formal and informal. Formal fallacies involve errors in the logical structure of an argument, where the conclusion does not follow from the premises regardless of content. Informal fallacies, which are far more common in everyday life, involve errors related to the content, context, or delivery of an argument rather than its abstract form. Major informal fallacies include ad hominem attacks, straw man misrepresentations, false dichotomies, appeals to authority, slippery slope reasoning, red herrings, circular reasoning, and hasty generalizations.
Studying logical fallacies equips learners to evaluate arguments more carefully, construct stronger reasoning of their own, and engage in productive dialogue rather than rhetorical manipulation. This topic bridges philosophy, rhetoric, and communication studies, and it has direct applications in media literacy, debate, legal reasoning, scientific discourse, and civic participation.
One step at a time.
A formal fallacy is an error in the logical structure of an argument where the conclusion does not validly follow from the premises, regardless of the truth of those premises. These fallacies can be identified by examining the argument's form alone.
Example: Affirming the consequent: If it rains, the ground is wet. The ground is wet. Therefore, it rained. The ground could be wet from a sprinkler.
An informal fallacy is an error in reasoning that arises from the content, context, or language of an argument rather than from its logical structure. These fallacies require understanding what the argument is about to identify the flaw.
Example: A commercial claims a toothpaste is the best because four out of five dentists recommend it, but the survey methodology is never disclosed.
An ad hominem fallacy attacks the person making an argument rather than addressing the argument itself. By targeting the speaker's character, motives, or background, the attacker tries to discredit the claim without engaging with its content.
Example: During a debate about climate policy, one speaker responds: You failed your science class, so your opinion on emissions data is worthless.
A straw man fallacy occurs when someone misrepresents or oversimplifies another person's argument, then attacks that distorted version instead of the original claim. This creates the illusion of having refuted the opponent.
Example: Person A says we should have stricter regulations on factory emissions. Person B responds: Person A wants to shut down all factories and destroy the economy.
A false dichotomy, also called a false dilemma, presents only two options as if they are the only possibilities when other alternatives exist. This fallacy pressures the audience into choosing between extremes.
Example: You are either with us or against us. This ignores partial agreement, neutrality, or conditional support.
An appeal to authority fallacy occurs when someone cites an authority figure as evidence for a claim, but the authority is not an expert in the relevant field, is biased, or their expertise alone is treated as conclusive proof.
Example: A celebrity endorses a vitamin supplement and a consumer takes this as proof it works, despite the celebrity having no medical training.
A slippery slope fallacy argues that a single action will inevitably trigger a chain of increasingly extreme consequences, without providing evidence that each step in the chain is likely.
Example: If we allow students to use calculators on this test, eventually no one will be able to do basic arithmetic. Each step is assumed without evidence.
A hasty generalization draws a broad conclusion from a small, unrepresentative, or insufficient sample of evidence. This fallacy ignores the need for adequate data before making sweeping claims.
Example: A traveler visits one restaurant, has a bad meal, and concludes the food in the entire country is terrible.
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Walk through a solved problem step-by-step. Try predicting each step before revealing it.
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