The Final Three (10-12) Logical Fallacies You Should Know

Abstract

Learn to challenge post hoc reasoning, appeal to ignorance, and bandwagon arguments. This will help you become a better critical thinker.

You've learned nine logical fallacies so far, and now it's time to master the final three. These last fallacies are sneaky because they often sound reasonable at first. But once you understand how they work, you'll spot them everywhere and know precisely how to respond.

Post Hoc: Confusing Coincidence with Cause

Post hoc is the same as "post hoc ergo propter hoc," which means "after this, thus because of this." This fallacy assumes that because one thing happened after another, the first thing must have caused the second. But timing alone doesn't prove causation; sometimes things are coincidences.

Example: "I started wearing my lucky bracelet, and I got an A on my next three tests. This bracelet is definitely helping my grades."

The bracelet might make you feel more confident, but it won't enhance your test scores in any extraordinary way. You likely studied with greater diligence, maintained focus in class, or found the material easier to understand. The timing is a coincidence.

How to Win: Look for other explanations and ask for evidence. You could say, "But you also started studying with Marcus around the same time, and his math skills are impressive." You've also been getting more sleep lately. How do we know it's the bracelet and not one of these other changes? By pointing out alternative causes, you show that correlation doesn't equal causation. You can also ask, "Would you get A's without the bracelet if you still studied hard?" This helps people understand that the real cause is something completely different.

Appeal to Ignorance: Proof by Lack of Proof

An appeal to ignorance claims that something must be true because no one has proven it false, or vice versa. This fallacy shifts the burden of proof to an unjustified position. The absence of evidence against something doesn't mean it is true.

Example: "Scientists haven't proven that Bigfoot doesn't exist, so Bigfoot must be real."

The lack of proof that Bigfoot doesn't exist isn't the same as proof that Bigfoot does exist. If this logic holds, we must believe in everything without clear disproof. That includes many imaginary creatures.

How to Win: Flip the burden of proof back where it belongs. Try saying, "Actually, the burden of proof is on the person making the claim. If someone says Bigfoot exists, they need to provide evidence. We can't prove that every imaginary creature doesn't exist - that would be impossible. The person claiming Bigfoot is real needs to show us some evidence." This approach works because it's impossible to prove a negative in most cases. You can't prove something doesn't exist anywhere in the universe. The person making the positive claim needs to support it with proof.

Bandwagon: Everyone is Doing It

The bandwagon fallacy asserts that something is accurate or good only because many people believe it. It assumes that if many people believe something, it must be correct. But popularity doesn't equal truth; history is full of examples where the majority was wrong.

Example: Everyone is buying those expensive wireless earbuds, so they must be the best ones available.

Because something is popular doesn't mean it's of the highest quality or the best value. People fall for it because of marketing, celebrity endorsements, or peer pressure, rather than for its superiority.

How to Win: Separate popularity from quality and ask for some proof. You could say, "Popular doesn't always mean best. Do you have actual reviews comparing sound quality, battery life, durability, or features? AirPods are popular partly because of Apple's brand recognition, not performance. Some less popular brands might actually be better for the price." This forces the conversation toward fair evidence instead of following the crowd. You can also mention when popular opinion missed the mark: "Remember when everyone thought hoverboards were so great?" Then they started catching fire."

You're now fallacy-proof.

Congratulations! You've now learned twelve of the most common logical fallacies. You can spot ad hominem attacks, straw man arguments, false dilemmas, slippery slopes, appeals to authority and emotion, hasty generalizations, red herrings, circular reasoning, post hoc reasoning, appeals to ignorance, and bandwagon arguments.

These tools make you an influential thinker. You can analyze arguments in class debates, political speeches, ads, and social media posts. Weak logic or emotional manipulation will not sway you.

Remember: the goal is to find the truth and make good decisions based on solid thinking. When you spot a logical fallacy, point it out and steer the conversation back to evidence and logic. That's how you become someone worthy of respect and trust: by valuing clear thinking and accuracy.

Credit where it's due:

https://www.law.cornell.edu/wex/posthoc

If you want to read about 7-9 of the 12 popular logical fallacies, you can find them here:

https://www.quarkstochlorophyll.blog/7-9logicalfallacies/

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