A logical fallacy is a flaw in the structure of reasoning: the conclusion doesn't actually follow from the reasons given, even when the words are compelling. Fallacies are dangerous precisely because they sound convincing. Learning to name them is the first step to answering them — and to building stronger arguments of your own.
One thing to hold onto first: a fallacy weakens this argument, not necessarily the conclusion. Someone can defend a true claim with terrible reasoning. Spotting the fallacy tells you the argument fails to support the claim, not that the claim is false.
Fallacies of misdirection
These win by changing the subject.
Straw man
Misrepresenting someone's position so it is easier to attack. "You want to relax this rule? So you want total chaos." The real, more moderate position never gets addressed.
Ad hominem
Attacking the person instead of their argument. "You'd expect that view from someone who failed economics." Whether they failed economics has nothing to do with whether their point is sound.
Appeal to emotion
Substituting a strong feeling — fear, pity, pride — for a reason. "Think of how frightened your family would be without this alarm system." Fear is not evidence that the product works.
Fallacies of false structure
These smuggle in a broken logical shape.
False dilemma
Presenting only two options when more exist. "Either we cut the whole programme or we go bankrupt." Usually there is a third, fourth, and fifth path the framing hides.
Slippery slope
Claiming one step must lead to an extreme outcome, with no evidence for the chain. "If we let students retake one test, soon nobody will study at all." Each link needs support; asserting the cascade is not the same as showing it.
Circular reasoning
Using the conclusion as one of its own premises. "This book is trustworthy because it says so itself." The argument never actually leaves the starting point.
Fallacies of weak evidence
These lean on evidence that cannot carry the weight.
Appeal to authority
Treating a claim as true only because an authority said it. "A famous doctor endorses this supplement, so it must work." Expertise is a reason to take a claim seriously, not proof — and the authority may be speaking outside their field.
Hasty generalization
Drawing a broad conclusion from too few examples. "Two friends disliked that city, so nobody enjoys visiting." A tiny, unrepresentative sample gets promoted to a rule.
Post hoc
(Post hoc ergo propter hoc — "after this, therefore because of this.") Assuming that because B followed A, A caused B. "I wore my lucky socks and we won, so the socks did it." Sequence is not causation; the two events may share a cause or none at all.
Why persuasive can still be wrong
Persuasion measures how an argument feels; validity measures whether the conclusion genuinely follows. The two come apart constantly, because advertising, debate, and social feeds all reward feeling over structure. That gap is where fallacies live.
A quick note on why they overlap with statistics: post hoc is the everyday cousin of confusing correlation with causation. One event following another is exactly the pattern that tempts us to invent a cause, when a confounding factor or plain coincidence may be responsible.
Spotting them in the wild
The skill is naming the move as it happens. Watching an ad or a heated thread, ask: Is the opponent's view being distorted (straw man)? Am I being offered only two choices (false dilemma)? Is a feeling standing in for evidence (appeal to emotion)? Did one thing get blamed just for coming first (post hoc)?
A good exercise: catch one argument today — in an advertisement, a post, or a conversation — name the fallacy it uses, then rewrite it as an honest argument without the trick. Often the conclusion still stands on better legs; sometimes it collapses. Either outcome teaches you something.
Keep learning: continue with the Critical Thinking foundations lessons on cognitive biases and correlation versus causation to see how these reasoning traps connect.