Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Multiple Choice question about Proposition Logic

  1. Oct 31, 2008 #1
    The question is here: http://dl.getdropbox.com/u/175564/logic.png [Broken]

    The correct answer is D.

    My attempt to the problem:
    Let the beginnings of the sentences be A.
    In a, A is B -/-> C is D.
    In b, A is B -/-> C is D.
    These first two do not make sense.

    in c and d, the word "only" suggests exaggeration.
    In c, A is B -/-> B must be C.
    In d, A is B -/-> A must be C.

    Still, I am sure thoroughly why d is the correct answer.
    Please, let me know why.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 12, 2009 #2


    User Avatar
    Gold Member

    You need modal logic here, for cannot and mustn't, which are modalities.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook