Self-study
Marine biologists had hypothesized that lobsters kept together in lobster traps eat one another in response to hunger. ████████ ████████ ██ ███████ ██████ ████████ ███ ████████ █████████ ██ ████████ ███████ █████ ████████ ███ ██████ █████ ████████ ████ ██████ ███ ████ ████████ ███ ███ ██████ ███████ ██████ ███ ████████ ███ ██████ █████████████ ███████████ ██████████ ██ ███████ ██████
Argument Breakdown: Phenomenon-Hypothesis
The argument concludes that marine biologists are wrong; trapped lobsters do not eat each other due to hunger. This is based on some observations of lobsters kept trapped together: they can sometimes share traps for weeks, and even in one case two months, without eating each other.
The argument is based in phenomenon-hypothesis reasoning: it claims to disprove the marine biologists' hypothesis due to finding evidence that is incompatible with that hypothesis. So we need to ask if the observations of trapped lobsters are really incompatible with the hypothesis.
Objective: Identify a Necessary Assumption
These observations only harm the biologists' hypothesis if the trapped lobsters observed were hungry. If lobsters only eat once every six months, for example, then the argument stops making sense. Another necessary assumption is that the lobsters observed were representative of the full range of lobster behavior. If trapped lobsters ate each other only sometimes, it would be possible to make these observations despite the biologists' hypothesis being true.
We can hunt for our predicted necessary assumptions in the answer choices. If we find one, great! Otherwise, we can revert to process of elimination using the negation and/or must be true tests.
14.
The argument against the marine █████████████ ██████████ ██ █████ ██ █████ ███ ██ ███ █████████ ████████████
a
Lobsters not caught ██ ███████ █████ ████ ████ ████████ ██████ ███ ████████
(A) would actually weaken the argument; it's certainly not necessary. If even non-trapped lobsters eat each other, that makes the biologists' hypothesis that trapped lobsters eat each other much more convincing.
b
Two months is ███ ███████ █████ ██████ ██████ █████ █████ ██ ████ ████████ ████ ████ ███████ █████████
How long a large number of lobsters has shared a trap doesn't matter to the argument as long as it's long enough to show they won't eat each other. Setting an upper limit definitely doesn't help: if lobsters had been trapped for even longer without resorting to cannibalism, that would be even stronger evidence.
c
It is unusual ██ ████ ██ ████ ██ █████ ████████ ██████ ████████ ██ ███ ██████ █████
The eight-lobster trap is used as evidence that lobsters don't eat each other even in a crowded situation. The argument implies it's unusual, but it being unusual is still not necessary. Even if it were normal to have very crowded traps, that wouldn't undermine the argument; the observed lobsters still didn't eat each other.
d
Members of other ██████ ███████ █████████ ███ █████ ███ ████ ████ ██ █████ ████ ███████ ███ ██████████
(D) gives us evidence consistent with the biologists' hypothesis, and therefore running counter to the argument. (D) may weaken; it definitely isn't necessary to assume.
e
Any food that ███ █████ ████████ ██ ███ ████ █████ ████ ████████ ███ ███ ██████ ██ ████ ███ ███████
(E) is part of the broader necessary assumption that the trapped lobsters were in fact hungry. If the trapped lobsters had plentiful food, then that would explain why they didn't eat each other. To demonstrate that lobsters don't cannibalize when hungry, the lobsters have to actually be hungry.