Logical Fallacy

IB 2025

Argumentum ad Misericordiam

Attempting to win an argument by appealing to emotion or pity rather than logic or evidence. Example; “You should give me an A on this essay because I worked so hard and I’m under a lot of stress.”

Affirmation of the Consequent

A formal fallacy where someone assumes that because the consequent is true, the antecedent must also be true. Example; “If it rains, the ground gets wet. The ground is wet, so it must have rained.”

Ambiguity

Using unclear or double meanings of words or phrases to mislead or misrepresent. Example; “Nothing is better than eternal happiness. A sandwich is better than nothing. Therefore, a sandwich is better than eternal happiness.”

Special Pleading

Applying standards or rules to others while exempting oneself without justification. Example; “Yes, everyone should pay taxes—but I work so hard, so I deserve an exception.”

Argumentum ad Antiquitatem

Claiming something is right or better simply because it’s traditional or has always been done that way. Example; “Marriage has always been between a man and a woman, so it should never change.”

Argumentum ad Baculum

Using threat, fear, or intimidation to make someone accept a conclusion. Example; “Agree with my policy, or you’ll lose your job.”

Argumentum ad Crumenam

Assuming something is true or better because the person who says it is wealthy. Example; “He must be right about investing—he’s a billionaire!”

Argumentum ad Hominem

Attacking the person making the argument instead of addressing the argument itself. Example; “You can’t trust her opinion on politics—she’s never even been to college.”

Argumentum ad Ignorantiam

Claiming something is true because it hasn’t been proven false—or vice versa. Example; “No one has proven aliens don’t exist, so they must be real.”

Argumentum ad Lazarum

Assuming someone’s argument is correct because they are poor or humble. Example; “He must be honest—he’s poor and lives a simple life.”

Accentus

Changing the meaning of a statement by emphasizing certain words or parts of it. Example; “I didn’t say she stole the money” (implying someone else did).

Argumentum ad Nauseam

Believing something is true because it’s been repeated so often. Example; “Everyone keeps saying it, so it must be true.”

Argumentum ad Novitatem

Assuming something is better or true simply because it’s new. Example; “This new app must be better—it just launched last week!”

Argumentum ad Numerum

Believing something is true because many people believe it. Example; “Millions of people believe in astrology—it must be real!”

Straw Man

Misrepresenting someone’s argument to make it easier to attack. Example; “You say we should regulate guns—so you want to ban all firearms!”

Equivocation

Using a key term or phrase in an ambiguous way with different meanings in different parts of the argument. Example; “A feather is light. What is light cannot be dark. Therefore, a feather cannot be dark.”

Illicit Process

In a syllogism, this occurs when a term is distributed in the conclusion but not in the premise. Example; “All cats are mammals. No dogs are cats. Therefore, no dogs are mammals.”

Non Sequitur

A conclusion that does not logically follow from the premises. Example; “She drives a nice car, so she must be smart.”

Red Herring

Introducing an irrelevant topic to divert attention from the main issue. Example; “Why worry about climate change when unemployment is still a problem?”

Post Hoc, Ergo Propter Hoc

Assuming that because one thing happened after another, it was caused by it. Example; “I wore my lucky socks, and then we won—my socks caused the win!”

Quaternio Terminorum

A syllogism that has four distinct terms instead of three, making it invalid. Example; “All cats are animals. All dogs are pets. Therefore, all cats are pets.”

Shifting the Burden of Proof

Making the opponent prove your claim false instead of proving it true. Example; “Prove that ghosts don’t exist!”

Argumentum ad Populum

Claiming something is true because it appeals to popular desires or emotions. Example; “Everyone wants this policy, so it must be good!”

Fallacy of Interrogation

Asking a question that assumes guilt or a controversial presupposition. Example; “Have you stopped cheating on your tests?”

False Analogy

Comparing two things that are not truly alike in relevant aspects. Example; “Employees are like nails—you have to hit them on the head to get them to work.”

Hasty Generalization

Drawing a broad conclusion based on a small or unrepresentative sample. Example; “My neighbor is rude, so everyone in this city must be rude.”