Formal Logic help

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• 1 Like

  FaviPapi-1-1 Member

  July 2020 edited July 2020 313 karma

  Some As are Bs: As <---S---> Bs

  All Cs are Ds: Cs ---> Ds

  No Bs are Cs: Bs ---> ~Cs

  Linking them will look something like this:

  As <---S---> Bs ---> ~Cs
  ~Ds ---> ~Cs

  (I can't find a way to connect Bs and ~Ds to ~Cs, but if you are writing this down, you should connect them...)

  Anyway, the inferences are:

  1. As <---S---> ~Cs
  2. ~Bs <---S---> Ds

  I hope this helps!
• errrrr1452 Alum Member

  July 2020 132 karma

  @FaviPapi Thank you for the reply. How did you make the inference ~B <--s--> D? I am having trouble making that inference.
• 1 Like

  FaviPapi-1-1 Member

  July 2020 edited July 2020 313 karma

  Here is how you do it:

  If we have these two conditional statements:

  X —> Y

  Z —> Y

  We can’t infer anything...

  However, if we take the contra-positive of those two conditional statements, we get the following:

  ~Y —> ~X

  ~Y —> ~Z

  From there we can infer that ~X <—S—> ~Z

  The reason behind that is the following: ~X and ~Z must share some common-ground or, as JY says, some interception because ~Y is brought into ~X and ~Z...

  I hope this helps - good luck studying!
• errrrr1452 Alum Member

  July 2020 132 karma

  @FaviPapi Thank you so much!!
• FaviPapi-1-1 Member

  July 2020 313 karma

  Of course, let me know if you have any other questions.