Lesson 8 Formal Logic Drill pg. 34

[g_lawyered]

Hi,
I've read the full Formal Logic PDF and am working on the drills and reviewing with Answer Key. On #7 of the Drill: Diagramming and Making Inferences, I correctly wrote the diagram but made an inference that's not on the answer key.

My diagram: E S WH

My inference: E WH

Inference explanation: I know that we can't combine "Some" and "Most" statements nor 2 "Some" statements to make any inferences. But in this case this is an "All" and "Most" statement. From what I read/understood from the PDF explanation it stated that because the Logic Ladder is: All, Most, Some that we can make inferences from All Some.

Can someone please explain why my inference is incorrect and why the Answer Key states there are No Inferences to be made?

Thanks in advance!

[Dave Killoran]

Hi G,

Try this approach:

• Start at WH. Now what do you get when you ride over to S? Going backwards over the "most" you get "some."
  
  Now, you've arrived at S in a "some" relationships. Is there an All or None arrow leading away? No. So there's no inference.

The problem here is that only certain combinations of "All" arrows with "Some" or "Most" will yield an inference, and here the arrows are not aligned properly/in the right order. These two give you inferences:

• A B C
  
  A B C

These two do not:

• A B C
  
  A B C

All of these Formal Logic drills will seem impossible until you get the above down straight, so stop for a moment and review this until it makes sense

[g_lawyered]

Hi Dave,
Thank you for explaining that. To clarify, when you say that the problem is that the arrows aren't aligned properly (since they don't point away from "Some") do you mean in the inference you stated about
WH S. Or did you refer to the arrows in the original diagram?

Also, we can't we start the inference from E because this original diagram states: E A WH , correct?
So, the only way possible to have made an inference was to start with WH as you stated. Did I understand that right?

Thank you!

[Dave Killoran]

Hi Dave,
Thank you for explaining that. To clarify, when you say that the problem is that the arrows aren't aligned properly (since they don't point away from "Some") do you mean in the inference you stated about
WH S. Or did you refer to the arrows in the original diagram?

I mean this in relation to: E S WH

When you start at WH and then arrive at S, you need an all/none arrow pointing away from S to make an inference. I urge you to go back and read the Some Train explanation here—it explains this all in detail and is critical to this all making sense!

Also, we can't we start the inference from E because this original diagram states: E A WH , correct?
So, the only way possible to have made an inference was to start with WH as you stated. Did I understand that right?

Thank you!

You can, actually. You won't be able to make an inference their either, as you'd again need an All or None arrow away to make an inference. No matter where you start there, there's no inference

Thanks!

[g_lawyered]

Hi Dave,
After re-reading the "Some" train and you're explanation it makes better sense.
Thanks again!