Another fallacy of presumption assumes there are fewer choices than there really are.
Key idea
A false dilemma presents two options as the only ones when others exist, then pushes you toward one by rejecting the other.
Why it works
An either-or argument is valid: if it is A or B, and not B, then it is A. So the whole weight rests on the either-or premise. If there is a third option, that premise is false, and the argument proves nothing.
Worked example: Find the missing option
Coach: "Either we practice four hours a day, or we'll lose every game."
- Are those the only two possibilities?
- No: practicing a bit more, or practicing more wisely, are other choices.
Answer: False dilemma.
Worked example: A real either-or
"A whole number is either even or odd. 7 is not even, so it is odd."
- Is there a third option? No: every whole number is even or odd.
- With the either-or true, the step to "7 is odd" is good reasoning.
Answer: Not a fallacy.
When you meet an either-or, try to finish the sentence "Or we could…". If you can, the dilemma is false, and the argument needs a new premise that rules your option out.
Common mistake
Treating every either-or as a false dilemma. "The light is on or it is off" really covers the cases. The fallacy needs a missing option. Test: can you name a third choice?