ABSTRACT
In ‘A Counterexample to Modus Ponens’ (The Journal of Philosophy LXXXII, 9, September 1985, pp. 462–71), Vann McGee presents the following alleged counterexample to modus ponens (he also presents two others which, however, are constructed in essentially the same way):
Opinion polls taken just before the 1980 election showed the Republican Ronald Reagan decisively ahead of the Democrat Jimmy Carter, with the other Republican in the race, John Anderson, a distant third. Those apprised of the polls results believed, with good reason:
If a Republican wins the election, then if it’s not Reagan who wins it will be Anderson.
A Republican will win the election.
Yet they did not have reason to believe
If it’s not Reagan who wins, it will be Anderson. (p. 462)
