pt 45 s1 q 21

jmac800

I have a question on how the video comes to the contrapositive of the answer choice.

"there are many records of major meteor impacts that do not seem to have been followed by mass extinction"

in the stimulus
becomes

""...then all major meteor impacts would be followed by mass extinction"

I understand we need
P ---> -CCL
or
CCL---->-p

And that this is to be P3. But how is all the contrapositive of many? Many could potentially be All. Shouldn't the right answer here be not many aka none, no, etc?

jmac800

Bump could someone answer?

nye8870

“There are many records of major meteor impacts that do not seem to have been followed by mass extinction.” Logically written:
Major Meteor Impacts – some-> /Followed By Extinction
When we negate, becomes:
Major Meteor Impacts --> Followed By Extinction
Ac(A) says logically: CCL --> (MMI --> FBE)
I believe what it says in English is, “If there is a consistent causal link then Premise 3 is incorrect.”
Try referring to this as well: http://7sage.com/lesson/the-negation/

jmac800

I'm unclear how negation of
Major Meteor Impacts – some-

becomes

Major Meteor Impacts

This is saying that the negation of some is all. I don't see the video you linked answering that. Some can include all. Ie. Some days it rains. What is the negation of this. All days it rains or not some days it rains. I believe it is the later, not some, and not some = it never rains. How can the negation of it rains some days be it rains all days? It is logically inconsistent.

nye8870

We need to negate some are -not-.... which is "all are".