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  • Posts: 243
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So the conclusion states : So unless steps are taken to re-establish the spiny cactus population, the dwarf masked owl will not make its home one the baja peninsula..

I diagrammed this as:

If owl makes its home on Baja peninsula :arrow: steps must reestablish spin. cact. pop

Contra positive: steps not taken rest. spin cactus pop. :arrow: owl wont make home on baja peninsula

So D is a mistaken reversal correct? But can someone explain why E is the correct answer , am I looking for an answer choice that mirrors the contra positive or the original conditional statement.

 Robert Carroll
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Answer choice (D) is indeed the Mistaken Reversal of that connection. As such, it is not an assumption required by the argument, so it's a wrong answer. There is one thing you missed in the stimulus:

spiny cactus :arrow: nesting sites

The lack of spiny cactus indicates that there are no suitable nesting sites for the owl, but the conclusion is that the owl will not make its winter home there. There is a gap between nesting sites and the winter home location. Thus, you need to connect those two things. This is why answer choice (E) is correct:

winter home :arrow: nesting sites

and its contrapositive:

nesting sites :arrow: winter home

Then you can say:

spiny cactus :arrow: nesting sites :arrow: winter home

And the conclusion of the argument is just the chain of conditionals above.

Robert Carroll
  • Posts: 243
  • Joined: Jan 10, 2018
So to understand your previous post correctly:
No Cactus Population → No Nesting Site
No Cactus Population → No Home on the Baja Peninsula
No Nesting Site → No Home on the Baja Peninsula
Home on the Baja Peninsula → Nesting Site (Contrapositive)

But the stimulus states there are no other suitable nesting sites for the dwarf masked owl on the Baja peninsula, but I don't think it was clear enough to represent this as No Cactus Population → No Nesting Site.

So would another way to approach this question involve taking the conclusion Home on the Baja Peninsula → Cactus Population, and identify an answer that would defend the necessary part, that the cactus population is suitable? Or am I just working backwards here?
 Adam Tyson
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I have to disagree with you, LSAT_2018. We are given that the spiny cacti are the only suitable nesting sites - there are no others. That can absolutely be diagrammed as:

Spiny Cacti :arrow: Suitable Nesting Site

and the contra-positive:

Suitable Nesting Site :arrow: Spiny Cacti

There is nothing in the stimulus that indicates, as you did in your question, that "the cactus population is suitable" is a necessary condition. That is a mistaken combination of a sufficient condition with a necessary condition into one condition.

Follow the steps Robert outlined here. The premises tell us that because the cacti are gone, there are no suitable nesting sites any more. The conclusion tells us the owls won't make their home there this winter. Connect the ideas of "no nesting sites" from the premises to the concept of "not make their home there" in the conclusion, and you will have your answer. Then, if you have any doubt, apply the Negation Technique to see whether the negated version of the answer in question ruins the argument.

Keep at it!

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