examples of confusing SC + NC errors

fycw2068fycw2068 Alum Member
in Logical Reasoning 404 karma

Hi everyone,

I tried searching in the discussions and the CC but wasn't able to find what I'm looking for... feel free to redirect me if there's already a lesson/thread that covers this.

Can anyone provide me with an example of a Flaw type problem where it mistakes a necessary condition for a sufficient condition as well as a problem where it mistakes a sufficient condition for a necessary condition?

I conceptually understand what mistaking one for the other looks like when written in lawgic but would like to see how this looks like in an LSAT problem.

Thank you!

Comments

  • Lucas CarterLucas Carter Alum Member ⭐
    edited May 2019 2804 karma

    An example might sound something like this:

    In Topanga, the most popular local ice cream shop, Redd's, is the only one on Main Street. Every ice cream product that the shop sells comes with sprinkles. Jones was walking down Main Street eating an ice cream cone with sprinkles, therefore he must have just come from Redd's ice cream shop.

    Edit: Here is an example from the CC that also contains a flaw similar in nature: https://7sage.com/lesson/experimental-psychology-pf-question/

    JY refers to this flaw as "The oldest trick in the book" because in some form or another it makes an appearance on every test.

  • 2ndTimestheCharm2ndTimestheCharm Alum Member
    1810 karma

    Lucas' yummy story is an example of when an argument mistakes a necessary condition for a sufficient one.
    premise: Every ice cream product sold by Redd's (the only ice cream shop on Main Street) has sprinkles. RICP->Spr
    conclusion: Therefore, every ice cream product with sprinkles (being eaten on Main Street) was sold by Redd's. Spr->RICP

    For fun, I'll make up a different argument that mistakes a sufficient condition for necessary one. If someone else can link to real PT examples, that would be awesome.
    premise: If you're afraid of clowns, that's all I need to know to consider you my friend. AC->F
    conclusion: Therefore, if you are my friend, you must have a wicked fear of clowns. F->AC

  • fycw2068fycw2068 Alum Member
    edited May 2019 404 karma

    Thanks for these examples!

    @"Lucas Carter" said:
    JY refers to this flaw as "The oldest trick in the book" because in some form or another it makes an appearance on every test.

    That's actually the exact line that had me wondering... I know that it's the "oldest trick in the book" but feel like I haven't 'seen it in the book' yet ;)

    @2ndTimestheCharm said:
    premise: If you're afraid of clowns, that's all I need to know to consider you my friend. AC->F
    conclusion: Therefore, if you are my friend, you must have a wicked fear of clowns. F->AC

    So in a problem, does it come down to which condition the conclusion emphasizes/how the conclusion is structured? Because when you write it out in lawgic, it seems like mistaking an SC for NC is notated the same as mistaking an NC for SC.

    lawgic:
    P: A --> B
    C: B --> A

  • 2ndTimestheCharm2ndTimestheCharm Alum Member
    1810 karma

    Yes, it does. And I agree with you that this crucial understanding is much easier to understand in a vacuum than in the LR phrasing - and that's no accident. The test writers only have so many sneaky weapons in their bag of tricks. They are sometimes straining to conform their arguments (or purposefully not conform them) to basic logic to see if we can recognize valid and invalid argument forms when they are hidden deep within the context of confusing language. But we will not let them get away with this! We will practice recognizing this flaw backwards and forwards until we beat them at their own game.

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