Two Negative Premises

Two Negative Premises

 * If A is not B, and B is not C, then A is C. This is always invalid logic (although it may happen to be true), as it is not possible to make a valid conclusion from two negative premises; logic is not arithmetic. This is a fallacy because simply identifying what something isn't doesn't identify what it is.

"No Jews are Muslims. No Muslims are Christians. Therefore Jews are Christians."

"No dogs are reptiles. No reptiles are magenta. Dogs are magenta."

"No dogs are reptiles. No reptiles shoot lasers out of their eyes. Dogs shoot lasers out of their eyes."

Well, how about: "No crow is a stone. No stone has wings. Therefore, crows have wings."


 * that's called a Fallacy Fallacy

Which could just as easily be: "No dog is a stone. No stone has wings. Therefore, dogs have wings."