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The existential fallacy, or existential instantiation, is a formal fallacy. In the existential fallacy, ''we presuppose that a class has members'' when we are not supposed to do so; that is, when we should not assume existential import. One example would be: "''Every unicorn definitely has a horn on its forehead''". It does not imply that there any unicorns at all in the world, and thus it cannot be assumed that, if the statement is true, somewhere there is a unicorn in the world (with a horn on its forehead). The statement, if assumed true, only implies 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, 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 . ==See also== *Vacuous truth 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Existential fallacy」の詳細全文を読む スポンサード リンク
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