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I Weird statement of conditions in propositional logic

  1. Aug 30, 2016 #1
    So I am studying conditionals in proposition logic, and I have discovered that there are a variety of ways to phrase a conditional "if p, then q" in English. Some of the harder ones are...

    p is sufficient for q
    a necessary condition for p is q
    q unless ~p (where ~ is the not operator)
    p only if q
    a sufficient condition for q is p
    q is necessary for p

    Do I just need to brute force memorize these? Or is there a way to really understand them? Some of them just seem so counter-intuitive...
  2. jcsd
  3. Aug 30, 2016 #2


    Staff: Mentor

    The second and fifth say the same thing in slightly different words.
    The fourth is the converse of p if q (which is the same as if q then p).

    An alternative to rote memorization of these is to understand the truth table for ##p \Rightarrow q##.
    Code (Text):
    p.|..q...|..p → q
    Hope that helps...
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