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Existential fallacy
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<h2 id="overview">Overview</h2> <p>An existential fallacy is committed in a medieval <a href="/facts/Categorical_syllogism/cgpmd6jB">categorical syllogism</a> 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. </p><p>In modern logic, the presupposition that a class has members is seen as unacceptable. In 1905, <a href="/facts/Bertrand_Russell/SRpwNX2U">Bertrand Russell</a> wrote an essay entitled "The Existential Import of Proposition", in which he called this Boolean approach "<a href="/facts/Giuseppe_Peano/VT2Wsmu7">Peano</a>'s interpretation". </p><p>The fallacy does not occur in <a href="/facts/Enthymeme/kjWtCDKa">enthymemes</a>, where hidden premises required to make the <a href="/facts/Syllogism/cgpmd6jB">syllogism</a> valid assume the existence of at least one member of the class. </p> <h2 id="examples">Examples</h2> <ul><li>All trespassers will be prosecuted.</li> <li>Therefore, some of those prosecuted will have trespassed.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a></li></ul> <p>This is a fallacy because the first statement does not require the existence of any actual trespassers (stating only what would happen if some do exist), and therefore does not prove the existence of any. Note that this is a fallacy whether or not anyone has trespassed. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Affirming_the_consequent/dK0zDWFB">Affirming the consequent</a></li> <li><a href="/facts/Quantifier_(logic)/bgmvwxoo">Quantifier (logic)</a></li> <li><a href="/facts/Vacuous_truth/QBsue3pP">Vacuous truth</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://www.fallacyfiles.org/existent.html">Fallacy files: existential fallacy</a></li> <li><a href="https://web.archive.org/web/20040623081418/http://www.swif.uniba.it/lei/foldop/foldoc.cgi?existential+fallacy">FOLDOC: existential fallacy</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Logical Fallacy: The Existential Fallacy". www.fallacyfiles.org. <a href="http://www.fallacyfiles.org/existent.html" target="_blank">http://www.fallacyfiles.org/existent.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> </ol>