Self-study
As the title states, I just need a bit more clarification on how to know when I need to find an answer that asks me to identify the missing link, rather than an answer that, if negated, would weaken the argument.
I recently attempted this question and was stumped to find that I needed to find an answer that was the missing link.
1
1 comments
Necessary assumption is a crucial part of the LSAT, and it is often a very obvious, very boring answer. That is why we use the negation test for necessary assumption questions; if we negate the answer choice and it destroys the conclusion, then we are need that answer choice to draw the conclusion. As to PT102.S4.Q25:
The dwarf masked owl, a rare migratory bird of prey, normally makes its winter home on the Baja peninsula, where it nests in the spiny cactus. In fact, there are no other suitable nesting sites for the dwarf masked owl on the Baja peninsula. But a blight last spring destroyed all of the spiny cacti on the Baja peninsula. So unless steps are taken to reestablish the spiny cactus population, the dwarf masked owl will not make its home on the Baja peninsula this winter.
I approached by digesting each sentence individually. I identify which are premises and conclusions. Sometimes I have to write the diagram out, but after some practice it'll come more naturally.
DMO winter in Baja --> spiny cactus
/spiny cactus --> /suitable nesting site (suitable nesting site --> spiny cactus)
last spring, destroyed all spiny cacti, or in other words: /spiny cactus
/reestablish spiny cactus --> /DMO winter in Baja
This is the crux of our argument:
DMO winter in Baja --> spiny cactus
suitable nesting site --> spiny cactus
We need to bring back the spiny cactus, or else the DMOs will not winter in Baja. Why? Why do they have to winter in Baja anyway? Why can't they just chill in Baja without the spiny cactus, even if there are no other suitable nesting sites? Can't they just find some other similar unsuitable shelter? We need something to connect our premises to the conclusion that DMOs will not winter in Baja. If we link up the conditionals, we can see a little more clearly:
DMO winter in Baja ? suitable nesting site --> spiny cactus
We need something to connect DMO winter in Baja to suitable nesting site. That is the necessary assumption we need to make, and the answer choice (E):
Suitable nesting sites must be present where the dwarf masked owl makes its winter home.
In other words, if DMO winter --> suitable nesting site.
So altogether, DMO winter in Baja --> suitable nesting site --> spiny cactus
The reason why the negation test works is because if we negated it -- suitable nesting sites need not be present where DMOs winter -- then our conclusion no longer stands. The DMOs don't need the spiny cacti and can still nest in Baja for winter. But again, our conclusion must be that they will NOT nest in Baja for winter.
This seems like a lot, but it's only because I wrote out each step! It'll come more easily once you practice (I still get NA questions wrong too!), and I would recommend doing some NA questions in a drill untimed. There will be a point where you won't need to diagram every single NA question.
Also remember, that the negation test will not always work for SA questions. SA is a different kind of assumption but is similarly linking a gap in our stimulus.