Inherent Inference Recognition Drill #5

[smarsh13@terpmail.umd.edu]

Hey! Quick question. I'm using the LR Bible 2020 edition and I'm struggling with drill #5 on page 441.

Would the translation of AFR <——s——> RP be "airlines sometimes fly a route if the route is profitable" or "some airlines fly a route if the route is profitable"?

My confusion is where to place the "some" in these statements.

Thanks!

[Jon Denning]

Good question! The answer is that both of those interpretations would necessarily be true/correct if we take the original statement as true: if all airlines always fly when a route is profitable (that's one half of the double-arrow original), then it must be the case that (1) some airlines fly when a route is profitable, and (2) airlines sometimes fly when a route is profitable.

You can do the same with the "most" implications: (1) most airlines fly when a route is profitable and (2) airlines fly most of the time when a route is profitable.

The great thing about statements containing language as strong/absolute as "all" (or "always") is that they typically guarantee a number of softer-language claims, as we see in this example, so really it just becomes about semantics in recognizing the various ways you can state those softer claims and the multiple constructions that still hold true. Good catch in considering a few different potential interpretations here!

[lsat2022]

I'm a bit confused with this one as well. Do we interpret "if and only if" as "all with " which is why we get both "most" and "some" inherent inferences?

Thank you!

[Dave Killoran]

Hi LSAT,

Yes, "if and only if" always produces a double arrow. Thus, "most" and "some" are inherently underneath that in both directions.

So, if "All As are Bs," then inherently Most As are Bs, and Some As are Bs. With a double arrow instead of a single arrow, those inherent inferences then go in both directions.

Thanks!

[askuwheteau@protonmail.com]

Good evening,

I couldn't find how to create a separate forum thread for this post. I'm hoping that someone can help me out. I'm currently studying Chapter 13 of the LR Bible (2023 Edition) which deals with Formal Logic. Number #5 in the Inherent Inference Recognition Drill (pg. 425) states that "Airlines fly a route if and only if the route is profitable". I properly diagrammed this as a biconditional: FR<>P. While the answer key (pg. 427) shows I got the original diagram correct, I can't understand the inherent inferences provided. Here it is stating that the most relationships can go in either direction. This doesn't make sense, as the chart on pg. 419 clearly states the most relationships are non-reversible relationships.

I don't want to move on in this chapter until I understand what is going on here.

Thanks,

Jonathan

[Stephanie Oswalt]

Good evening,

I couldn't find how to create a separate forum thread for this post. I'm hoping that someone can help me out. I'm currently studying Chapter 13 of the LR Bible (2023 Edition) which deals with Formal Logic. Number #5 in the Inherent Inference Recognition Drill (pg. 425) states that "Airlines fly a route if and only if the route is profitable". I properly diagrammed this as a biconditional: FR<>P. While the answer key (pg. 427) shows I got the original diagram correct, I can't understand the inherent inferences provided. Here it is stating that the most relationships can go in either direction. This doesn't make sense, as the chart on pg. 419 clearly states the most relationships are non-reversible relationships.

I don't want to move on in this chapter until I understand what is going on here.

Thanks,

Jonathan

Hi Jonathan,

I moved your post to the thread discussing this question. Please review the above discussion, and let us know if this helps. Thanks!

[askuwheteau@protonmail.com]

Hi Stephanie,

Thanks for referring me to the post above. Dave's explanation made sense. I only don't understand why the master conditional statement (the All biconditional) changes the usual unidirectional rule for the most statements. Would you please clarify on that (my book doesn't address this concept in detail)?

[Dave Killoran]

It doesn't. It's the presence of two arrows that makes it go both ways.

A B

Can be broken into:

A B

AND

B A

At that point, "most" and "some" statements inherently sit under each:

A B
A B
A B


AND

B A
B A
B A

So it's not the double-arrow making some change to the "most," it's that there are two statements there (and thus the two arrow directions) which is making it work like that.

Please let me know if that helps. Thanks!

[askuwheteau@protonmail.com]

Good morning Dave,

Thank you for clarifying. I had my aha moment when you mentioned the parts which make up the biconditional (double arrow statement). Consequently, I returned to the LR Bible pg. 223 re the Double Arrow. I now understand perfectly.

FYI, I'm currently concentrating on LR and RC patterns that I'm seeing as I go through the results of my PrepTests. I started on Chapter 13 (Formal Logic), but stopped partway due to prioritizing other weaknesses of mine. If I don't end up totally finishing chapter 13 before retaking my LSAT in April of 2025, would I expect to encounter much if any Formal Logic questions on the real test-day exam?

Your advice is most appreciated,

Jonathan Sloan

[Jeff Wren]

Hi Jonathan,

I see that this question was addressed to Dave, but I'm happy to give you my two cents in the meantime.

While Formal Logic hasn't been as common on the recent LSATs as it had been in years past, I'd still recommend that you complete that chapter prior to taking your LSAT. Since you're not planning on retaking the test until April 2025, that should be more than enough time (assuming that you have a decent amount of free time to study in those nine months).

Also, since the test is currently undergoing a major change with the removal of the logic games section, it is possible that there will be more formal logic questions in LR going forward in order to test skills similar to those in logic games. I'd recommend checking back in the fall/winter when we should have a better sense of any new trends.

That being said, it is certainly reasonable to focus on other problem areas that appear more frequently first.