First Principles
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A reasoning game · think for yourself

Spot the flaw
in the argument.

Read the claim. Find the weak link. Learn the name for it. Every round is an everyday argument that breaks one of logic's oldest rules — once you can name the move, you can't un-see it.

0 of 18 mastered
Round 1 of 18 Name the fallacy
01
The claim
“Everyone at school is switching to this app — so it's obviously the best one out there.”
The field guide — all 18 fallacies
Attack the person
Ad Hominem

Attacking the character or motives of the person making an argument instead of engaging with the argument itself.

If the rebuttal is about the speaker rather than the claim, it's ad hominem.
Misrepresentation
Straw Man

Distorting or exaggerating someone's position into a weaker version, then attacking that version instead of what they actually said.

Ask: did they really say that? A caricature you can easily knock down is the tell.
Forced choice
False Dilemma

Presenting only two options as if they were the only possibilities, when other choices or middle ground exist.

Watch for "either/or" framing — then look for the options it conveniently left out.
Chain of doom
Slippery Slope

Claiming one modest step will inevitably trigger a chain of increasingly dire consequences, without evidence for the chain.

Each link in the "and then…" chain needs proof. Asserting the chain isn't showing it.
Borrowed credibility
Appeal to Authority

Treating a person's status, title, or fame as proof of a claim — especially when they're speaking outside their expertise.

Expertise can be evidence; celebrity isn't. Ask what the actual data says.
Too few cases
Hasty Generalization

Drawing a sweeping conclusion from a sample that is too small, biased, or unrepresentative.

"I met one, therefore all of them…" A handful of cases rarely settles a rule.
Begs the question
Circular Reasoning

An argument whose conclusion is smuggled in as one of its premises — it assumes the very thing it claims to prove.

Strip out the restatements. If the reason just repeats the conclusion, it's circular.
False cause
Post Hoc

Assuming that because one event followed another, the first must have caused the second (post hoc ergo propter hoc).

Order in time isn't causation. Could it be coincidence or a third cause?
Feelings over reasons
Appeal to Emotion

Using fear, pity, pride, or anger to win agreement in place of a relevant reason or evidence.

Strong feelings can be real and still prove nothing. Ask for the actual reason.
Appeal to popularity
Bandwagon

Claiming something is true, good, or right because many people believe it or do it.

Popular and correct are different facts. Crowds can be wrong together.
Move the goalposts
No True Scotsman

Defending a generalization against a counterexample by redefining the group to exclude it ("no real X would do that").

When a counterexample appears and the definition suddenly tightens, that's the move.
Distraction
Red Herring

Introducing an irrelevant topic to divert attention away from the actual question being argued.

Ask: does this answer the question, or just change the subject?
You too
Tu Quoque

Deflecting criticism by charging the critic with the same fault, instead of answering the criticism (appeal to hypocrisy).

"Well, you do it too" doesn't make the original point wrong. It dodges it.
Absence of proof
Appeal to Ignorance

Arguing a claim is true because it hasn't been proven false — or false because it hasn't been proven true.

Not-yet-disproven isn't the same as proven. The burden of proof stays put.
Word-switch
Equivocation

Using a single word or phrase in two different senses within the same argument, so the conclusion only seems to follow.

Spot the key word that quietly changed meaning between sentences.
Hidden assumption
Loaded Question

A question built on an unproven assumption, so that any direct answer forces you to concede that assumption.

If both "yes" and "no" admit something you never agreed to, the question is loaded.
Throwing good after bad
Sunk Cost Fallacy

Continuing a course of action because of resources already spent, rather than the value of going forward.

Past spending is gone either way. Decide on the future payoff, not the buried cost.
Forced sameness
False Equivalence

Treating two things as equivalent when they differ in scale or kind in ways that matter to the argument.

"Both sides do it" only holds if the things are actually comparable. Check the size and kind.