Qualifiers and Valid/Invalid Arguments

lbalestrieri

Hey everyone! I've been reviewing valid and invalid argument forms this afternoon, and I'm having a bit of trouble so any help would be greatly appreciated! I'm trying to relate valid and invalid argument forms in terms of qualifiers and inferences that can be made from them - it's giving me a better and helpful perspective when evaluating arguments. From the LSAT Trainer I know that using the qualifier some + some = no inferences; some + most = no inferences; and most + most = inferences. First, is this a correct way to relate valid v invalid argument forms? It seems to me that it works to differentiate the two, but I'd like someone else's thoughts on that before I begin to rely on it.

For example: this is a valid argument because we can infer from "most" + "most" (Valid Argument Form 9)
A most B
A most C
_________
B some C

However this is not a valid argument form (Invalid Argument Form 7): because we cannot make inferences from "some" + "some"
A some B
A some C
_________
B some C

Second, going off of this information, I'm a bit confused on 7sage's Invalid Argument Form 6 which is:
A most B most C
_______________
A some C

7sage gives the example of: Most cats are mammals. Most mammals are not cats. Some cats are not cats. - And clearly that "english" example makes no sense. But I am a bit confused on how that translates into "lawgic". I know from the Miscellaneous group of logical indicators that is/are "are predicates that point to their subjects and say those are necessary". So am I correct to "translate" this invalid english argument to be:

Mammals most Cats
Not Cats most Mammals
_____________________
Not Cats some Cats

Using the logical indicators this makes sense to me, but I'm struggling to see how this example mirrors Invalid Argument Form 6 that I referenced above so I feel I am translating incorrectly and would appreciate someones correction. This english statement was also given with it: Most A’s are B’s. Most B’s are C’s. Therefore, some A’s are C’s - but using actual examples is most helpful to me - but, like I said, I'm struggling to relate the given english example with the lawgic and I'm not sure what I am doing wrong when translating the statement given that it does not match the Invalid Argument Form 6 lawgic.

Hope this all makes sense, and thank you for any help/response!

emli1000

I feel that the easiest way to memorize these forms is to actually make flash cards and go over them a couple of times. I did this about 5 times in a row & I was able to recognized all valid & invalid forms afterwards.

emli1000

This was how I did it

https://www.examtime.com/en-US/p/1495595

https://www.examtime.com/en-US/p/1509201

lbalestrieri

Thank you! That's very helpful to help me memorize them! I'd still like to understand how I'm mis-diagramming the Misc. group of logical indicators with that second question with the mammals/cats example, so if anyone has any insight I'd love to hear it!