Chapter Text, Question #4

[Amyers1313]

P. 192
I got the correct answer B but with the presence of Without in 3rd sentence, a "planets climate is too extreme and unstable to support life" becomes un-negated becoming "planet climate able to support life" expressed as

PCE GI

contrapositive as

GI PCE

You are showing the contrapositive as

GI PCE

please explain
Thank you kindly!! This is really fun btw

[Dave Killoran]

Hi Amyers,

Thanks for the question! The good news is that there is not an error here, and the diagrams shown in the LRB are correct Let's look at that third sentence and see what's going on with the diagram:

• "Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life."
  
  This sentence is given in the form of: "Without A, B." In such a case, apply the Unless Formula, which produces the following diagram:
  
  B A
  
  So, returning to our sentence, what we get is:
  
  planet’s climate is too extreme and unstable to support life stable and moderate axis tilt
  
  That is correctly shown on page 193 in shortened form as PCE AS. In this case, and as I reference in the next paragraph, it's critical to realize that PCE = planet’s climate is too extreme and unstable to support life.

My thought here is that the PCE term caused the difficulty for you, because it's saying it's not too extreme (in which case it means that the planet's climate can support life). From your statements, you understood that. But, your use of PCE for the sufficient condition does not mean that, and that's why things look different. It appears to me that you mis-diagrammed the sufficient condition (or at least used the wrong acronym for what you wanted), but actually understood the underlying meaning. That would allow you to arrive at B while still having your diagram look different.

The key thing here is that diagramming is just a tool to help make things clear, and if you can understand something without diagramming it, then you don't need to diagram it

Please let me know if that helps. Thanks!

[Amyers1313]

Yes helps a great deal.

I got hung up on the negation and the effect on the content.

This is really FUN btw.

Thank you!!
Amy