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Q. 5 of Quiz on drawing valid conclusions with translation 3

Alum Member
in General 36 karma
In JY's breakdown of this statement:
All dinosaurs that hunt its prey can run, swim and fly. Dinosaurs that cannot run, cannot swim or cannot fly are easy to catch and delicious to eat. Nothing can catch the Fastasaurus.
He diagrams "Dinosaurs that cannot run, cannot swim or cannot fly are easy to catch and delicious to eat" as R/---> E and D, S/---> E and D, F/---> E and D. When it was actually drawn out R/, S/, and F/ were all stacked and each pointed to a single E and D. But this doesn't make sense to me. Isn't it the case that an "And" in the sufficient should be treated as "A and B----->" and an "And" in the necessary be treated as "A ----->B, A----->C, A-----> D" but in a stacked notation? Why does JY do the opposite? He stacks and separates the sufficient "AND" and makes the necessary "And" linear.
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• Alum Member
edited December 2016 192 karma
I notice that in the first sentence of the blockquote there's an "and", implying that all hunting dinosaurs can do all three kinds of locomotion. But in the second sentence, there's an "or", implying that there may be dinosaurs that can do only one or two kinds.
• Alum Member
192 karma
P.S. For questions like this, a link to the original source video and/or lesson that generated it is a great convenience.
• Live Member Sage 7Sage Tutor
10746 karma
@"Spencer D" said:
All dinosaurs that hunt its prey can run, swim and fly.
Dinosaurs that cannot run, cannot swim or cannot fly are easy to catch and delicious to eat.
Hey, so I could not find the lesson you were referencing to. But take a look at the 2nd sentence, that's not an "and" its an "or". So based on the 2nd sentence, we actually have an "or" in the sufficient. Because of that you have the /R, /S, /F as separate, because each of them is sufficient to give you "easy to catch" and "delicious to eat".

Also, when "and" is in "necessary", its easier to write it separately. For example if A then B and C. You can keep the "and", but its so much easier to see it when its linear. Because when "A" triggers, both "B" and "C" also trigger. So it means the same thing. If you want to keep the "and" in neccessary its your call. But consider this scenario. If "C" then D. And lets say I tell you, that "D" does not exist. So if we take a look at the way you wanted to write it,

A-->B and C--> D
But now if we negate it we are stumped because we can have /D and /C but B in.
But had we written A-->B A-->C-->D. Negating D now allows for that and its much easier.

Although in your scenario the "and" in necessary wasn't wrong. It just doesn't make it easy to chain up a complex conditional statement.

* I hope this was helpful.

P.S. Next time post the link. It took me a while to understand what was being asked. Sorry