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If 2+2=5, then bertrand russel is the pope!

  1. Jul 8, 2003 #1
    Inconsistant logical systems are not useful in getting at "the truth". The following is a cute "proof" by Bertrand Russel:

    If 2+2=5...
    that means 4=5...
    so, lets subtract 2 from each side...
    that gives us...
    transposing, we have 3=2...
    now, lets subtract 1 from each side...
    Now, since the Pope and Russel are two different people, and 2=1...
    Therefore, the Pope and Russel are one.
  2. jcsd
  3. Jul 8, 2003 #2


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    It's not necessary to be that complicated.
    In general, If p is a false statement then
    p=> q
    is true for any statement q:

    The direct statement: "if (2+2= 5) then Bertrand Russel is the pope" is a true statement.
  4. Jul 8, 2003 #3
    There is an anecdote about this demonstration (I do not know if this really happened).It is said that during a public lecture Russell was making the remark that from a contradictory set of axioms practically everything can be deduced.At this a man from the public interrupted the lecture and challenged him to prove that from 4=5 results that he is the Pope.Which he brilliantly did...

    In another sequence of ideas [my comments are general,possible you know very well,I do not intend to sell flowers to the gardener] the necessity to avoid internal incoherences is what make epistemology so important:its task in mathematics and applied sciences is to establish whether the scientific hypotheses (or the axioms of mathematics) are coherent therefore acceptable logically:all sets of premises (including axioms) must have internal consistence.Indeed in order to be experimentally adequate all scientific hypotheses must pass first the logical test.

    Is logic a feature of reality?Well,there is no necessary connection between ontological reality and logic (since logic is a feature of human reasoning).From the fact that we understood so many facts about nature using conceptualizations based on logic does not follow that this will always be the case;in fact there are enough many scientists who are skeptical about the prospects of finding a 'theory of everything' exactly due to this problem.
    Anyway,as Einstein once remarked,it is a real miracle that we have been able to understand so many things so far...
    Last edited: Jul 10, 2003
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