How do you convert these sentences into logic? Are these valid or invalid arguments and why?

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• Accounts Playable Live Sage ⭐

  November 2015 edited November 2015 3107 karma

  "Or" rules can be sometimes confusing since the English language is sometimes vague about inclusiveness or exclusiveness. Unless explicitly stated by the LSAT, always assume the inclusive or.
  
  1.) Not run for office----->I shut my mouth. Contapositive: Not shut my mouth--->run for office. I ran for office (so we affirm the necessary condition; rule irrelevant). We cannot conclude that I didn't shut my mouth; this argument is invalid. Also, in this scenario, since we are assuming inclusive or, it is possible to both shut my mouth and run for office.
  
  2.) I am literate--->I can read and I can write. Contrapositive: I cannot read or I cannot write--->I am not literate. I can read: this just affirms one element of the necessary condition, so we cannot conclude anything. I cannot write: here we know something. This is one of the sufficient conditions in the contrapositive. Thus, you must conclude that you are not literate. This argument is valid.
  
  Link to the first "or" lesson: http://7sage.com/lesson/why-is-or-so-confusing/
  
  Hope this helps!
• 2 Likes

  nye8870 Alum ⭐

  November 2015 1749 karma

  Nice explanation @"Accounts Playable" ! I would just add this: When the LSAT means for an "or" statement to exclusive, it will appear as "either x or y, but not both" which gets you a logical conversion of x <--> /y. The contrapositive of course is y <--> /x. These become very important in LG such as In/Out because then you know either x or y must be in, without the possibility of both In.