A fallacious disjunctive syllogism assumes an inclusive disjunction is exclusive. If A or B can be true (or both), affirming A does not exclude B.
Example
“You can eat or drink.”
“He is eating, therefore he is not drinking.”
(The disjunction was inclusive.)
Applied example (superstitious)
“Either the amulet protects or the prayer protects.
I have the amulet, so the prayer does not work.”
(Exclusivity is assumed without basis.)
Why it is fallacious
- It confuses inclusive “or” with exclusive “or”.
- It denies a possibility that remains open.
- The conclusion does not follow from the premise.
How to spot it
- The alternative was not exclusive.
- “Not B” is inferred just because A is true.
- No clarity about exclusivity.
How to respond
- Ask whether the disjunction is exclusive or inclusive.
- Show that both options can coexist.
- Restate the premise clearly.