LSAT 152 | Section 2 | Logical Reasoning: Q19

QUESTION TEXT: Some species of tarantula make good pets…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Not every tarantula species has poison fangs.

REASONING: Tarantula SOME good pets ➞ poison fangs

ANALYSIS: This is a good argument. It correctly combines a some statement with a conditional statement. Note that you have to take the contrapositive of the conditional to make the link above.

So, look for a conditional where you must take the contrapositive to combine it with a some statement. Skimming answers to look for structural cues is a key skill. Only three answers have a single some statement, and one of them has an impossible conclusion (based on the evidence). So only two answers are worth considering.

Note: This deduction with a “some” statement and an “all” statement is an important form to learn. Let’s see how it works. Basically, you can always connect a “some” statement to the sufficient conditional, but not to anything else.

Suppose we have these two statements:

Some cats are black

All cats have tails

We can draw these two statements together like this: Black SOME Cats ➞ Tails

They connect on the sufficient condition, Cats. And the new deduction we get is: “Some Black things have Tails”. We know this is true because some cats are black, and those cats have tails (like all cats).

This works for any some statement where it has a variable in common with the sufficient condition in an all statement. You can also combine “most” statements in this way. Absolutely essential to learn this diagramming combination.

___________

1. CORRECT. This exactly parallels. The evidence combines like this: “Collection SOME regular meter ➞ written by Shawn“
   This lets us conclude that some poems in the collection weren’t written by Shawn.
2. This has two “some” statements as premises. I skipped over it as soon as I read that. You can’t combine two “some” statements.
   On parallel questions, it’s important to know when to skip an answer as “almost certainly wrong” without detailed analysis. To parallel the stimulus, you need an all statement.
    
   But, to show this argument is wrong, let me give a numerical example. The argument doesn’t set a limit on the size of the collection. It could include every poem in the world, including all of Shawn’s.
    
   In which case, all of Shawn’s poems would be in the collection and this conclusion is wrong. The fact that some poems in the collection don’t have regular meter is irrelevant. The collection has every poem in the world, so we’d expect it to include both poems with and without a regular meter.
3. This answer does have a conditional statement and a “some” statement, so it at least has the right form. Let’s see how we can combine them. The conditional statement here is: “written by Shawn ➞ not in this collection” You can only attach a “some” statement to a sufficient condition. So, the only way you can combine the premises is like this: “Regular meter SOME written by Shawn ➞ not in this collection”
   So, se could only conclude that some poetry outside the collection has a regular meter (Because some of Shawn’s poems aren’t in the collection and don’t have regular meter). But, the conclusion is about poems in the collection, so it isn’t supported by the argument.
   (“Written by Shawn” is an odd point to connect two statements, and at a glance it suggested to me that this answer was probably wrong. I focused on A first)
4. This argument completely fails to work. The conclusion talks about “unpublished poetry”, but none of the evidence mentions publication. (It’s possible for a collection to be unpublished).
   So you can skip this without further analysis. It’s literally impossible to form this conclusion if none of the evidence mentions publication.
5. This answer doesn’t have a “some” statement, so it cannot parallel the argument.

Recap: The question begins with “Some species of tarantula make good pets”. It is a Parallel Reasoning question. Learn how to master LSAT Parallel questions on the LSAT Logical Reasoning question types page.

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