Think Through the Issue
Test 23 - Section 2 - Question 6
Logical Reasoning Difficulty: 1
LSAT Demon user Jonathan F. says, "I picked C, but I think I figured out why it's D. My initial guess before reading the stem was, "Wait, what if the humans went into the forest and brought back some chimpanzee tools? That could blow a hole in the 'it has to be a human tool' theory. That's why C jumped out at me. It matched what I predicted. When I was skimming through the rest of the answers, I think I was predisposed to think they were wrong, which also tripped me up. D makes sense because since we're talking about prehistoric time, you'd have to assume that these habitats stayed the same throughout history. It's much stronger than C."
Thanks Jonathan! I love getting questions like this. Jonathan has clearly thought the issue through. Now he's checking to make sure his understanding is correct. This is the best kind of question an LSAT teacher can get. Keep asking these questions and you're gonna do great.
Jonathan's reasoning is mostly correct, but goes off the rails at the very end. Jonathan's last line makes me concerned that he doesn't understand the Necessary Assumption question type. Lots to unpack here:
"What if the humans went into the forest and brought back some chimpanzee tools?"
This is a solid objection. If humans did go into the forest and bring back chimp tools, the argument would be destroyed. Unfortunately, that doesn't make C the correct answer. On a Necessary Assumption question, we're looking for the answer that the author must agree with. Another way of saying that: We're looking for the answer that. when false, will make the argument lose.
The author does not have to agree with C.
So what if humans sometimes ventured into the forest? That doesn't mean they brought anything back, let alone tools, let alone chimp tools. C can easily be false without ruining the argument. It's incorrect because the author does not have to agree with it.
"D makes sense because since we're talking about prehistoric time, you'd have to assume that these habitats stayed the same throughout history."
Mostly correct. The argument relied on the fact that the tools were found in a savanna, where prehistoric humans lived but chimps did not. The argument hasn't really assumed that the habitats "stayed the same throughout history"—that's far too strong. The argument has assumed that the savanna where the tools were found wasn't a forest full of chimps when the tools were being used. If the area where the tools were found was a forest full of chimps, the argument would immediately fail. The author must agree that D is true. The argument makes no sense if D is false. That's why D is the answer.
"It's much stronger than C."
No, it's not. Actually, it's the exact opposite. Saying the savanna where the tools were found was not a forest when the tools were in use is narrowly tailored to the argument. It's specific, yes, but it's not "stronger." Necessary Assumption questions prefer weaker answers because it's harder to prove something strong. C is actually stronger here. It applies to all times throughout history. And not only does it say that chimp tools weren't brought back from the forest, but it also says that humans never even set foot in the forest! It's far too strong to make a likely candidate for a Necessary Assumption question.
C is not the answer precisely because it's too strong. D is the answer because it's not too strong—the author would be forced to agree, at a bare minimum, that the exact location where the tools were found wasn't forest at the exact time the tools were in use. If D is false, the argument loses. That's the hallmark of a correct Necessary Assumption answer.
While I'm here:
A is wrong because if humans did not carry their tools with them when they traveled from place to place, then tools, no matter where they are found, could be human tools. How would that hurt the argument? The author doesn't have to agree with A.
B is wrong because the author takes no position on the entirety of East Africa for the entire time since primates first evolved. This is a horrible answer for a Necessary Assumption question because it's way too broad and way too strong.
E is wrong because it's irrelevant whether chimps were capable of using these tools, or more sophisticated tools. The author has presented evidence that the tools were found in an area where chimps don't currently live. E ignores that evidence and starts rambling about the tool-using capabilities of chimps. So what?
Thanks again for your question Jonathan! You're doing great.