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What is 'or'?

  1. Jun 23, 2015 #1
    In logic a or b is true if both a and b are true but do you think the everyday or is in fact xor ?
  2. jcsd
  3. Jun 23, 2015 #2


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    In logic, a or b is true, if at least one among a and b is true.
    The everyday or can mean either xor or the logical or, sometimes one and sometimes the other. The meaning is usually obvious from the context.
  4. Jun 23, 2015 #3


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    xor is usually NOT the everyday meaning of or.
  5. Jun 23, 2015 #4
    I disagree:
    • you can have meat or fish for dinner
    • I won't be back until Tuesday or Wednesday
    • my bet for the winners of the World Cup is Germany or England
    • are you going to vote for the liberal candidate or the conservative?
    • this problem should take five or ten minutes
    I can think of some everyday "inclusive or"s though:
    • I am waiting for a number 14 or a number 52 bus
    • the committee is quorate if there are three members present including the Chairman or Treasurer
    Bored with this now...
  6. Jun 24, 2015 #5


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    All of your examples are for things that are mutually exclusive. In those situations xor and or are identical.
  7. Jun 24, 2015 #6
    True for most of the first list, but (i) that merely illustrates the point that very often "or" in everyday speech is exclusive; and (ii) it is certainly possible to have both meat and fish for dinner, but this would not normally be the way "you can have meat or fish for dinner" is interpreted.
  8. Jun 26, 2015 #7

    jim mcnamara

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    How about this sound bite:

    A: Is it 3:00pm or 4:00pm?
    B: Yes.

    This is an xor response and is almost never used (except by math types making jokes) in normal English speech. Most educated people impliclty get it, but think the responder is being difficult or pedantic, almost never funny. My personal experience only.
  9. Jun 26, 2015 #8


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    I don't understand what you mean by this. Are you contrasting xor with or? If yes, the answer "yes" doesn't depend on our interpretation of "or" here. The nature of time dictates that or and xor are equivalent in this example.
    By now, MrAnchovy's examples should've cleared everything up, I think.
  10. Jun 26, 2015 #9


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    I think this is more of a philosophy or sociology question, not a Mathematics or Logic question ( in neither sense of the word 'or' ;) )
  11. Jun 27, 2015 #10
    In common usage 'or' can correspond with the logical or, but sometimes with the logical 'xor'.
    The latter usage is not uncommon.
    For example 'Do you prefer oranges or apples?'
  12. Jun 27, 2015 #11


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    It's context dependent. If the context implies "either.. or" then it is xor. If the context implies "if a or if b", then it is not exclusive. Language is not consistently logical. There can be many exceptions, and it can depend on regional influences.

    Correction: "either.. or" is not always xor. It is xor only if "but not both" is implied. But I guess that makes my point.

    Added: If you like this subject, you should listen to NPR "A Way with Words". You might send them this question.
    Last edited: Jun 27, 2015
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