Here https://www.sfu.ca/~swartz/modal_fallacy.htm Pr Norman Swartz , author of " Possible Worlds: An Introduction To Logic And Its Philosophy" gives philosophically interesting examples of modal fallacies.
Can you think of other interesting examples?
Are there classic examples of modal fallacies in scientific thought, particulary in mathematics?
Incidentally, do modal notions have " the right of the city" in mathematics?
By a modal fallacy, I mean a fallacy implying modal notions such as " necessity", " possibility", " contingency".
For example:
(1) Necessarily, I will recover or I will die of this disease. (2) So, taking a medecine is pointless, for whatever I may do, I will recover necessarily or die necessarily.
OR
(1) What is true cannot be false. (2) It is true that Kennedy has been assassinated. (3) Therefore, it could not have benn the case Kennedy not to be assassinated, Kennedy's dead was inevitable.