#23 - The diet of Heliothis subflexa caterpillars

[Administrator]

Complete Question Explanation

Put aside all the science and Latin in this question, and underneath you will find a fairly straightforward and simple conditional reasoning problem with some formal logic also thrown in. The second sentence alerts us to this with the key words "many" and "necessary", and that sets up this formal logic relationship:

GMI (Growth and Maturation of Insects) LA (Linolenic Acid in diet)

The next sentence gives us a standard conditional relationship, also using the word "necessary":

PV (Produce Volicitin) LA

The last sentence gives us another formal logic statement, indicated by "most":

CS (Caterpillar Species) PV

Stringing that together as best we can, we can make this chain:

CS PV LA

That can be read as "Most caterpillar species produce volicitin, and all of those that do so have linolenic acid in their diets". That's the prephrase for this Must Be True question! There's not much that can be proved based on the first claim about growth and maturation, but we might consider using it if we don't find a better answer based on this nice chain.

Answer A: We have no way of knowing, based on the stimulus, whether H. subflexa synthesizes linolenic in its bodies, or in an Easy Bake Oven, or at all. There's no support for this, so it's a loser.

Answer B: This is the correct answer. This is a perfect match for our prephrase based on the formal/conditional chain we got from the third and fourth sentences of the stimulus.

Answer C: This is a mistaken reversal of the relationship found in the third sentence. MRs cannot be proven (even though they could be true), so this answer is a loser.

Answer D: New information about poison kills this answer choice, as Must Be True questions cannot lead to answers with new info not supported by the stimulus.

Answer E: Again, new information is the death of this answer. While we know that H. subflexa eats Physalis, we cannot know that nothing else does.

[mirelisg14]

Hi,

Thanks so much for providing the explanations for each answer choice - it helped me understand why B is the response that must be true. However, my conditional diagramming was different on two occasions:
1. the final sentence led me to the following conditional statement: HSC (H. subflexa caterpillars) ~PV. So I was looking for an assumption that involved the H. subflexa caterpillars.

2. I didn't (and still don't) understand the relationship between growth + maturation of insects and linolenic acid to be sufficient and necessary for each other (which is what I understand the double arrow to represent). I originally diagrammed it as: GMI LA (if you are an insect with growth and maturation, you have linolenic acid in your diet). Can someone please help me understand how the second sentence indicates that both terms are sufficient and necessary for each other?

Thank you!

[nicholaspavic]

Hi mirelis!

Welcome to the forum. This is an unusual question in that involves an area of logic that we call "Formal Logic." Formal Logic involves quantifiers like "some," "most," etc. That's probably why our diagramming of this stimulus may be confusing to you. Strict Formal Logic is a very infrequently tested idea on the LSAT, at around only 2% of LR questions. So on average 1-2 per LSAT. It is an area that we cover in the Logic Reasoning Bible and in our full online and in-person courses but because it is an infrequently tested concept on the modern LSAT, these type of questions are rare.

That second sentence is going to be tricky without Formal Logic diagramming skills but the words "many" and "necessary" are the indicator words that give rise to it. The stimulus is also tricky in that "growth and maturation" are qualities identified as belonging to "many" insects other than the HS caterpillar. Note how the stimulus is silent about whether HS has growth and maturation. That's partially why you are getting the double arrow with "some." Because we cannot in Formal Logic characterize the word "many" to mean "most" as many students are prone to do initially, we have to understand that "many" converts to "some." Now here's the fun part, when looking at certain terms, some of them can be reversed, and some of them cannot be reversed. For example, the following arrows are one-way:




Thus, when you have a statement such as A B, it only works in that one direction, and you can't "flip" the terms, meaning that B A would NOT be identical.

However, some arrows do reverse, including the following:





See how "some" is working there? That's why you are getting that double arrow!

Thanks for the great question and I hope this helps! If you have our study materials discussed above, let me know which one it is and I can point you to the drills to help you with this.

[mirelisg14]

Hi Nicholas,

Thanks so much - this was helpful. I'm actually taking an in-person Power Score course and we are at the tail end of it. Formal logic is not among my strongest suits on the exam. I struggle with quickly recognizing and diagramming it when it arises on LR (not as much on LGs), and tend to get them wrong on almost every practice exam I take! I'll be sure to continue reviewing it.

[nicholaspavic]

Hi mirelis!

Cool! Glad you are taking the class. There is a virtual module under Lesson 8 in the full-length LSAT course. Check that out to explore those concepts. It is really helpful! Good luck and we are here for you!

[andrewb22]

I did the pre-phrase drill with this question (covering the answers ---> read stimulus and pre-phrase ----> selecting the answer that fits my pre-phrase without looking at the stimulus) and I'm curious if I can improve my pre-phrase : "Linolenic acid is not necessary for growth in the H. Subflexa caterpillars."

While none of the answers fit that, before eliminating the rest, (B) stuck out to me as the correct answer solely off my pre-phrase. What would be a more accurate pre-phrase for this question?

[Ryan Twomey]

Hey Andrew,

So I would not have prephrased an exact answer choice here, because there was too much conditional logic to prephrase just one correct answer. I would have mapped out each conditional logic chain and then picked the answer that was validated from the conditional logic that I mapped out. Below is the conditional logic that I mapped out.

HS diet----->P Genus-----> Not L acid---->Not Vioctin

51% Caterpillar ------>Vioctin------> L Acid

There were a lot of answer choices that could have been correct based on my conditional logic, so I would not have pre-phrased just one answer. I would make sure you had all of these statements mapped out and connected.

I personally connect conditional statements as I go, especially focusing on any horizontal connections as this means deductions.

I hope this makes sense, and I wish you all of the luck in your studies.

Best,
Ryan

[kupwarriors9]

How did you know conditional reasoning was present? Thanks

Hey Andrew,

So I would not have prephrased an exact answer choice here, because there was too much conditional logic to prephrase just one correct answer. I would have mapped out each conditional logic chain and then picked the answer that was validated from the conditional logic that I mapped out. Below is the conditional logic that I mapped out.

HS diet----->P Genus-----> Not L acid---->Not Vioctin

51% Caterpillar ------>Vioctin------> L Acid

There were a lot of answer choices that could have been correct based on my conditional logic, so I would not have pre-phrased just one answer. I would make sure you had all of these statements mapped out and connected.

I personally connect conditional statements as I go, especially focusing on any horizontal connections as this means deductions.

I hope this makes sense, and I wish you all of the luck in your studies.

Best,
Ryan

[Robert Carroll]

kup,

There are several conditional indicators present in the stimulus: "entirely", "necessary", "necessary".

Robert Carroll