Grouping Setup Practice Drill #6

[Stephanie Oswalt]

We recently received the following question from a student. An instructor will respond below. Thanks!

Hello! On page 321 I would like to know how the first inference can be combined with the super rule to create C<-/->G

[Jonathan Evans]

Hi,

Good question! Check out the illustration below followed by a brief explanation:



Consider three scenarios:

1. What if B is selected? If B is selected, G must be selected (Rule 2) and C must not be selected (Rules 1 & 3 combined).
2. What if C is selected? If C is selected, B is not selected (Rules 1 & 3) and therefore G is not selected (Rule 4).
3. What if G is selected? If G is selected, B is selected (Rule 4) and C is not selected (Rules 1 & 3).

Notice in all three scenarios, there is no possible way C and G can be selected together, therefore: C G.

In the illustration above, you can see this link between the element in common between both statements, B.

I hope this helps!

[Diliabarron]

Thank you! Makes sense now.

[rwraulynaitis]

Hello,

I am working through the 6th question in the Grouping Setup Practice Drill. I got the answer correctly on my own, but in reading through the answer key on p. 341, I am confused about how the single arrow and the double not-arrow were combined.

I understand how we got: ~H -> L <-/-> M

but I do not see how that leads to the inference: ~H -> ~M

I would appreciate it if you would be able to clear this up!

[Dave Killoran]

Hi R,

Thanks for the question! So, we are looking at this relationship: H L M

Let's first start with H L M to see how it works. In this diagram, what you get is if you have H, then you have L, and if you have L then you do not have M. So, you get H M.

Now, look at when we start with: H L M. The only difference is that H has a slash on it now, for H. So, when we have H, then you have L, and if you have L then you do not have M. So, you get H M. Same exact process but this time we accounted for the slash on H.

Of course, the contrapositive of H M is in fact M H, which how we get that tricky inference.

Please let me know if that helps. Thanks!

[rwraulynaitis]

Got it, thanks Dave!