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Hey ya'll, I have a quick question to find out if the explanation I made for myself is correct.

Imagine these two arguments:

1. A-->B
2. AT LEAST 4 Bs are Ys
---
3. Answer: I can't make a valid conclusion.

BUT

1. A-->B
2. AT MOST 4 Bs are Ys
---
3. I can conclude that at most 4 As are Ys

Is the difference because "at least" is too vague to make a conclusion and "at most" is limiting enough?

Is there a better way to diagram "at most" and "at least" by the way????

And thanks in advance for any input!

I don't think that you can make a valid conclusion under both scenarios, we don't know enough about B to make any valid inferences. We need to know that All B's are Y in order to make any valid conclusions.

The thing is, this was the answer in an lsat book! I don't know if it has something to do with contrapositives or what.

You will really never come across something like this on the LSAT (coming from someone who has drilled every Cambridge LR packet & done PTs 40-72).

FWIW, like the above poster I'm also unsure whether #2 is a valid inference. The way to diagram this in the "LSAT sense," if there is one, would be A --> B <-Some-> Y. In this case no inferences can be made.

I'm not an LSAT book so Im not disputing what the books say per say but I learnt the hell out of those statements so I can tell you:

A some B
B----> C
Valid conclusion A some B

A most B
B------>C
Valid conclusion A most C

A----->B
B------>C
Valid conclusion A----->C

Main point, in all instance we know All Bs are Cs which allows us to make a valid inference. Also, if I'm wrong can someone correct me.

sashafierce wrote:I'm not an LSAT book so Im not disputing what the books say per say but I learnt the hell out of those statements so I can tell you:

A some B
B----> C
Valid conclusion A some B

A most B
B------>C
Valid conclusion A most C

A----->B
B------>C
Valid conclusion A----->C

Main point, in all instance we know All Bs are Cs which allows us to make a valid inference. Also, if I'm wrong can someone correct me.

You are definitely correct -- this is what the LR Bible refers to as the "some/most train." The "all" arrow has to lead away from the "some/most" arrow to draw a valid inference. OP, if this isn't clear I would strongly recommend the LR Bible or, even better, the 7Sage full course (J.Y. has about 20 lessons in which he discusses valid & invalid inferences that come up on LR).

I recommend the 7sage course as well. That's where I learnt it, he has a lot of useful drills that help you fully understand the concept.

Is the difference because "at least" is too vague to make a conclusion and "at most" is limiting enough?

Is there a better way to diagram "at most" and "at least" by the way????

You've got the right idea. The second pattern you gave yields a valid inference that at most four A's are Y's. Notice how vague and almost insubstantial a conclusion that is, it doesn't even imply that any A's are Y's. It just guarantees that it's less than 5 of an indeterminate number of A's can be Y's.

I imagine the point of the exercise in whatever book you're using is to show you exactly what commitments phrases like "at most" and "at least" create.

Okay, I see I made a mistake with the first one. It should matter whether it says "at least" or "some," right? Because I couldn't make a conclusion from that.

"At most" seems to be a different case because it limits, but if this isn't likely to show up on the test, I won't worry about it too much.

I'm actually taking the 7sage course as well! Just drawing from a lot of material, and this problem set confused me a bit.

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