Modal fallacy

It has been suggested that Modal scope fallacy be merged into this article. (Discuss) Proposed since September 2024.

The formal fallacy or the modal fallacy is a special type of fallacy that occurs in modal logic. It is the fallacy of placing a proposition in the wrong modal scope,^[1] most commonly confusing the scope of what is necessarily true. A statement is considered necessarily true if and only if it is impossible for the statement to be untrue and that there is no situation that would cause the statement to be false. Some philosophers further argue that a necessarily true statement must be true in all possible worlds.

In modal logic, a proposition ${\displaystyle P}$ can be necessarily true or false (denoted ${\displaystyle \Box P}$ and ${\displaystyle \Box \lnot P}$, respectively), meaning that it is necessary that it is true or false; or it could be possibly true or false (denoted ${\displaystyle \diamond P}$ and ${\displaystyle \diamond \lnot P}$), meaning that it is true or false, but it is not logically necessary that it is so: its truth or falseness is contingent. The modal fallacy occurs when there is a confusion of the distinction between the two.