Discussion
The goblin fern, which requires a thick layer of leaf litter on the forest floor, is disappearing from North American forests. In spots where it has recently vanished, the leaf litter is unusually thin and, unlike those places where this fern still thrives, is teeming with the European earthworm Lumbricus rubellus, which eats leaf litter. L. rubellus is thus probably responsible for the fern’s disappearance. Which one of the following is an assumption on which the argument depends?
*This question is included in June 2013 LSAT (PT69): Logical Reasoning A, question #19
| (A) | Wherever there is a thick layer of leaf litter in North American forests, goblin ferns can be found. |
| (B) | ... |
| (C) | ... |
| (D) | ... |
| (E) | ... |
| (F) | ... |
The solution is
Posted: 11/17/2013 00:06
Why is the answer E instead of B?
Posted: 11/18/2013 16:43
Hi, Jesse -
The problem asks you to find an assumption on which the argument depends. In other words, the correct answer is a statement that, if false, invalidates the argument.
Answer [B] is not strong enough to do this. Suppose that there are North American worms that eat leaf litter. If such worms have not been found "teeming" in areas where the goblin fern has recently vanished (as L. rubellus has), there is no reason to suppose that they, rather than L. rubellus, are responsible for the die-out.
On the other hand, if [E] is false and L. rubellus does favor environments where the leaf litter is too thin for goblin fern, then the argument is invalid, as in this case L. rubellus probably only began to multiply after the thick leaf litter (and thus the goblin fern) was already gone. Thus [E] is an assumption on which the argument depends, and is the correct answer.
Hope this helps! Please post again if you have further questions.
Best,
Lyn
The problem asks you to find an assumption on which the argument depends. In other words, the correct answer is a statement that, if false, invalidates the argument.
Answer [B] is not strong enough to do this. Suppose that there are North American worms that eat leaf litter. If such worms have not been found "teeming" in areas where the goblin fern has recently vanished (as L. rubellus has), there is no reason to suppose that they, rather than L. rubellus, are responsible for the die-out.
On the other hand, if [E] is false and L. rubellus does favor environments where the leaf litter is too thin for goblin fern, then the argument is invalid, as in this case L. rubellus probably only began to multiply after the thick leaf litter (and thus the goblin fern) was already gone. Thus [E] is an assumption on which the argument depends, and is the correct answer.
Hope this helps! Please post again if you have further questions.
Best,
Lyn