'Not all' lawgic

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• 1 Like

  Sami Live Member Sage ⭐ 7Sage Tutor

  August 2018 edited August 2018 10789 karma

  Instead of translating it into lawgic, I would suggest just trying to understand what it means to say ""Not all tarantula species have poison fangs."

  For example, If I write a parallel sentence -Not all apples are Red. Would you say then from this sentence I can now say -if something is not an apple its red? So if its a pear, was the sentence above sufficient to conclude now that Pears are red? Similarly, we cannot go from saying:

  "Not all tarantula species have poison fangs."

  to

  translate this as /T -> PF

  What about if I write, not all swans are black. Can we now conclude that some swans are black? I think you would disagree. Similarly, from the sentence above we cannot say,

  T <->some PF

  But if we think about it, "not all" just means there are some that this is not applicable to. So in our case of ""Not all tarantula species have poison fangs", it just means that there are some tarantula species that do not have poison fangs.

  If its helpful for you, see "not all" as the logical opposite of all. I think a lesson that can be really helpful is Advance negation in core curriculum.
  Here is the link: https://7sage.com/lesson/advanced-negate-all-statements/

  Hopefully this helps. Let me know if you have any more question.
• TheDeterminedC Member

  August 2018 1025 karma

  This gave me some trouble as well. I found that "not all" was just as confusing as "must be false EXCEPT."

  J.Y. teaches us to view "must be false EXCEPT" questions as could be true, which is a hell of a lot easier to understand. That said, I made a flashcard for "not all" and wrote on the back "some not," it's just intuitively easier to understand the latter and they are logically equivalent so why not.