LR Drill Set 5, Question 2
McClosky: Eighty percent of Neanderthal stone tools ever(38 more words not shown)
The reasoning in McClosky's argument(9 more words not shown)
- Athat stone tools(7 more words not shown)
- Bthat many stone(11 more words not shown)
- Cthat a greater(22 more words not shown)
- Dthat there may(10 more words not shown)
- Ethe number of(17 more words not shown)
Reading the argument
Eighty percent of how many tools?
At first, 80 percent sounds like much better odds than 30 percent. But those percentages describe two different groups. We know how common asymmetrical chipping is within each group. We don't know how large either group is.
Try actual numbers. Suppose there are 100 Neanderthal tools and 10,000 Homo erectus tools. Eighty Neanderthal tools would have the chipping, compared with 3,000 Homo erectus tools. Pick a chipped tool from those groups, and the much larger group supplies far more possibilities, despite its lower percentage.
Those numbers aren't facts we're adding to the passage. They show a situation the evidence allows in which McClosky's conclusion goes the wrong way. The missing information is the relative number of tools. The fact that chipped tools are more common among Neanderthal tools doesn't by itself mean a chipped tool is more likely to be Neanderthal.
What we’re looking for
That's what I want the flaw answer to capture. We don't need to explain how the chipping happened or decide who really made these particular tools. We need to identify why these two percentages can't settle that comparison.
Working the answers
- A
Repeated use might explain how a tool becomes chipped. But the argument uses the observed chipping to decide which group the tools more likely belong to. Whatever caused the chipping, we still need to know how many tools each group contributes. A supplies a possible cause without exposing the numerical problem.
- B
The conclusion compares Neanderthal with Homo erectus; it doesn't say Neanderthal is more likely than every other possibility combined. A third group could account for most chipped tools while Neanderthal still beats Homo erectus in their two-way comparison. B therefore doesn't explain why that particular comparison is unsupported.
- C
The relevant percentages describe tools as they are found, including any features that have worn away. Perhaps more Homo erectus tools were chipped thousands of years ago. That doesn't invalidate the stated 30 percent among the tools discovered now, which is the kind of evidence McClosky is using to classify another discovery. C shifts to a past appearance without supplying the missing group sizes.
- DCorrect
“Extant” means still existing. There could be vastly more existing Homo erectus tools, so 30 percent of that group could outnumber 80 percent of the Neanderthal group. Our example produced 3,000 versus 80. The conclusion treats the larger percentage as enough to establish the more likely source, without checking the size of the group behind each percentage.
- E
McClosky isn't using a few expedition tools to estimate a percentage for all tools. The argument applies already stated percentages to a discovery. A probability judgment can concern even one object; a small number of objects doesn't itself make that judgment defective. The relevant missing numbers are the relative populations of the two kinds of tools, not simply how many the expedition recovered.
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