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The question below made me confused because I thought the conditional statement "the painters must have needed to eat the sea animals populating the waters north of Norway if they were to make the long journey to and from the islands" was a fact because there is a Sufficent Condition that triggers a Necessary Condition there for it must be true. So when I learned A was wrong, I was confused because the conditional statement created a "rule." So, I need help. How do you disprove a conditional?
THE QUESTION:
Recently discovered prehistoric rock paintings on small islands off the northern coast of Norway have archaeologists puzzled. The predominant theory about northern cave paintings was that they were largely a description of the current diets of the painters. This theory cannot be right, because the painters must have needed to eat the sea animals populating the waters north of Norway if they were to make the long journey to and from the islands, and there are no paintings that unambiguously depict such creatures.
Each of the following, if true, weakens the argument against the predominant theory about northern cave paintings EXCEPT:
A. Once on these islands, the cave painters hunted and ate land animals.
B. Parts of the cave paintings on the islands did not survive the centuries.
C. The cave paintings that were discovered on the islands depicted many land animals.
D. Those who did the cave paintings that were discovered on the islands had unusually advanced techniques of preserving meats.
E. The cave paintings on the islands were done by the original inhabitants of the islands who ate the meat of land animals
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3 comments
To answer your question directly -- you can disprove a conditional by showing that the sufficient condition can be true, even if the necessary condition is false.
"A requires B."
How do we show that's false? By showing that A is possible without B. If A is possible without B, then A does NOT require B.
Does that help you understand why D weakens?
Also, I'll note that you aren't wrong, on a first glance, to think that "the painters must have needed....." is a fact/premise that we should accept as true. However, there are some rare cases in which the LSAT does present us with answers that weaken by suggesting a premise is false. This is arguably one of those cases. One signal that "the painters must have needed..." is particularly susceptible to questioning is that it's a speculative statement -- "must" in this context suggests the author doesn't know that the painters needed to eat sea animals, but rather is speculating that this is true because it sounds reasonable.