Logical fallacies
Identify logical fallacies in texts and speech: ad hominem, slippery slope, false dilemma, appeal to authority, circular reasoning, hasty generalisation.
In this lesson you will
- Name and explain common fallacies
- Identify fallacies in real-world texts
- Respond to fallacies constructively
Learn
Ad hominem: attacking the person, not the argument (You can’t trust her view on tax — she’s rich). Straw man: misrepresenting the opposing view. Tu quoque: You do it too.
Slippery slope: claiming one step will inevitably lead to extreme outcomes without evidence. False dilemma: only two options when more exist. Hasty generalisation: a broad conclusion from few cases.
Appeal to authority (when the authority is irrelevant or unqualified), appeal to popularity (millions can’t be wrong), appeal to tradition (we’ve always done it this way).
Circular reasoning: the conclusion is in the premise (This source is reliable because it says it is). Post hoc: A happened, then B, so A caused B. Responding: name the problem politely and redirect to evidence.
Examples
- Slippery slope: If we allow one food truck, soon the whole park will be a car park.
- False dilemma: Either you support this bill or you want children to suffer.
- Appeal to authority: A famous actor says this diet works, so it must.
- Circular: The book is true because it says it contains no errors.
Vocabulary
fallacy
a flaw in reasoning
ad hominem
attacking the person
slippery slope
claiming a small step leads to extreme results
false dilemma
presenting only two options
post hoc
assuming earlier means cause
In real life
Read the letter to a local newspaper.
“The council’s plan to add cycle lanes is a disaster waiting to happen. First cycle lanes, next they’ll ban cars altogether, and then the town centre will die. The councillor behind this scheme doesn’t even own a car, so what would she know about drivers’ needs? Either we protect motorists or we destroy local business — it’s that simple. My neighbour’s shop lost customers the month the new bike racks appeared, which proves my point. We have always driven into town, and that is how it should stay.”
Practice
“First cycle lanes, next they’ll ban cars…” is a…
Speaking
Respond to the letter writer politely in 90 seconds: name two fallacies and redirect the discussion to evidence.
Writing
Write a reply to the newspaper (180–220 words) that identifies at least three fallacies in the letter and makes a reasoned case.
Lesson quiz
Attacking the person, not the argument:
Review
Key points
- Ad hominem, straw man, tu quoque.
- Slippery slope, false dilemma, hasty generalisation.
- Appeals to authority, popularity, tradition.
- Circular reasoning, post hoc.
What you learned
- ✓ I identify logical fallacies.
- ✓ I explain why they fail.
- ✓ I respond constructively.