Existential fallacy
The statement, if assumed true, implies only that if there were any unicorns, each would definitely have a horn on its forehead.An existential fallacy is committed in a medieval categorical syllogism because it has two universal premises and a particular conclusion with no assumption that at least one member of the class exists, an assumption which is not established by the premises.In modern logic, the presupposition that a class has members is seen as unacceptable.In 1905, Bertrand Russell wrote an essay entitled "The Existential Import of Proposition", in which he called this Boolean approach "Peano's interpretation".The fallacy does not occur in enthymemes, where hidden premises required to make the syllogism valid assume the existence of at least one member of the class.