Logical Fallacies: 20 Pitfalls of Faulty Thinking

What Is a Logical Fallacy

A logical fallacy is an argument that seems convincing but violates the rules of valid inference or appeals to irrelevant factors. The ability to recognize them is one of the most practical intellectual skills. They are found in political speeches, advertising, courtrooms, business negotiations, and scientific debates.

Formal Fallacies

Affirming the consequent: “If it’s raining, the streets are wet. The streets are wet. Therefore, it’s raining.” Incorrect—the streets could have been washed. Form: P→Q; Q; therefore P. Wrong.

Denying the antecedent: “If it’s raining, the streets are wet. It isn’t raining. Therefore, the streets are dry.” Incorrect—they could have been washed. Form: P→Q; not-P; therefore not-Q. Wrong.

Informal Fallacies

Ad hominem—an attack on the person instead of the argument. “You can’t talk about economics—you’ve never run a business.” But the argument can be correct regardless of who said it.

Straw man—to distort an opponent’s position, making it easily refutable. “You say we need more regulation. So, you want the government to control our every move?”

False dichotomy—presenting a situation as a choice between two options, although there are more. “Either you’re with us, or against us.” “Either we lay off staff, or we go bankrupt.”

Appeal to authority—when the authority is irrelevant. A genius physicist recommending a diet is not an authority in dietetics. But appealing to a relevant expert is a legitimate technique.

Post hoc ergo propter hoc (“After, therefore because of”): a company changes its logo—sales increase. So, the logo helped? Not necessarily. Correlation does not imply causation.

Slippery slope—assuming that one action will inevitably lead to a chain of negative consequences. “If we allow remote work, employees will stop working altogether.” Each step must be justified separately.

Appeal to the people (ad populum)—the majority thinks so, so it must be true. “95% of Russians believe X. Therefore, X is true.” Historical example: at one time, most believed the Earth was flat.

Appeal to nature—“Natural” means good; “artificial” means bad. Cyanide is a natural substance. Vaccines are “artificial,” but they have saved billions of lives.

Gambler’s fallacy—the belief that past random events affect future ones. “Heads came up 10 times in a row. The next toss is surely tails.” A coin doesn’t remember the past.

Poisoning the well—discrediting the opponent before they speak. “You are about to hear a proposal from a person who has been to prison twice.”

Appeal to tradition: “We’ve always done it this way.” This is not an argument for continuing—it’s necessary to justify why the tradition is good.

Hasty generalization: a few cases → universal law. “Three startups from our incubator failed—therefore, our incubator is bad.”

False consensus effect: “All reasonable people agree that…”—anyone who disagrees is automatically declared unreasonable, without proof.

Appeal to pity: “Approve our budget—if not, we’ll have to fire 50 people.” An emotional argument may be relevant but does not substitute for substantive reasoning.

Appeal to novelty: “This is the latest technology—so it’s better.” New is not necessarily better.

Fallacy of division: a property of the whole is ascribed to each part. “Microsoft is a successful company. Therefore, every one of its employees is successful.”

Fallacy of composition: a property of the parts is ascribed to the whole. “Every player on the team is a champion. Therefore, the team is a team of champions.”

Tu quoque (“You too”): “You criticize smoking, but you drink yourself.” The critic’s behavior does not refute their argument.

How to Deal with Fallacies

Before pointing out a fallacy in your interlocutor’s argument—make sure you have correctly understood their position (principle of charitable interpretation: Steel Man instead of Straw Man). Indicate specifically which element of the argument violates logic, and why. Suggest a corrected version.

Question for reflection: Recall your last workplace discussion. Can you find examples of one of these fallacies in the arguments of your opponent—or your own?