Archaeologist: Our team discovered 5,000-year-old copper tools near a Canadian river, in a spot that offered easy acc...

Irene-Vera on June 30, 2019

Please explain

Can someone explain why B is right and why all other answers are not (explanation not needed for answer a) thank you!

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cjahangiri on September 23, 2019

Following up on this, why is B the correct answer?

AndreaK on September 24, 2019

Hi @Irene-Vera and @cjahangiri,

First off, let’s identify the question type. This is a necessary assumption. For a necessary assumption, we’re looking for an answer choice that provides a minimum amount of information we would need to have in order for the argument’s conclusion be possible. Note that we don’t need to prove the conclusion is true, since that’s what we do for a sufficient assumption question.

Something that helps on difficult necessary assumption questions is called the negation technique. Consider if an answer choice were not true. Could the conclusion still stand without it? If the argument can’t stand without the truth of an answer choice, you know you’ve found a piece of information that’s necessary to the argument.

Next, let’s break down the evidence and the conclusion. I like to start with the conclusion.

Conclusion: it is likely therefore that Aboriginal people in Canada built birchbark canoes 5,000 years ago.

Why is this likely?


5,000-year-old tools were discovered in a spot that offered easy access to materials for birchbark canoes, and because the tools are of a sort used by the region’s Aboriginal people in making birchbark canoes in more recent times.

So here are some thoughts I have. They’re using the fact that the region’s Aboriginal people use the tools today to make birchbark canoes as evidence for saying they were used 5,000 years ago to make birchbark canoes. Equating from today to 5,000 years ago is a bit of a leap. It could be the case that those tools were used for making huts for shelter and warmth 5,000 years ago instead. Maybe 5,000 years ago Canada was still stuck in the middle of an ice age and the rivers were perpetually frozen over. Then you wouldn’t even need a canoe, would you?

Additionally, they’re using the fact that these 5,000 year old tools were found near a river with easy access to canoe making materials as evidence for the fact that they were actually used to build canoes 5,000 years ago. Well, maybe a tribe of nomads from the American great plains wandered up through Canada, got hungry, stopped at the river for some ice fishing, and accidentally left their fishing tools behind there? Heck, maybe even yesterday somebody robbed a nearby museum, dumped everything they could grab into a duffle bag, booked it out of there on foot, ran off into the wilderness to hide from the cops, got slowed down by how heavy the booty was, so they dumped the heavy ancient tools used for building the great wall of china and just held on to Marie Antoinette’s diamonds instead. Far fetched maybe, but it shows that the fact that the tools were found there doesn’t prove that they were used by the region’s Aboriginal people to build canoes.

A) Trade value of the tools doesn’t effect the argument in any way.
B) Here we go. Think about what it would mean if the tools weren’t in the region 5,000 years ago? That opens a pandora’s box of a weakener. The tools could have been brought there by somebody else (our American ice fishing tribe, or our stealthy museum burglar). If it were not the case that the tools were actually present in the region 5,000 years ago, the argument would be seriously weakened.
C) “Only” in this answer choice is problematic. It’s strong language for a necessary assumption question, and we should be looking for weakly worded answer choices to prove something that’s necessary (as opposed to strongly worded answer choices to prove something is sufficient). Would it hurt the argument if the tools were designed to be used on birch, cedar, spruce AND pine trees? What if these tools were also used to make the people’s huts for shelter, and they used pine instead of birch for these because who doesn’t love a good natural built in air-refreshener? More organic than your Febreeze, I bet. This situation could totally be at play without weakening the conclusion at all. The pine scented huts wouldn’t make it any less likely that the Aboriginal people in Canada built canoes 5,000 years ago, so we know the argument isn’t relying on this information.
D) “Only” again at play here. Strong words for a necessary assumption. What if there were other tools the people used for canoe making? The conclusion wouldn’t be weakened if there were other tools they used in addition to these copper ones. We need to know the 5,000 year old copper tools were used for canoe making at least sometimes. But that doesn’t mean other tools couldn’t have been used too. What if the Aboriginal’s had their own 5,000 year old iron version of the Swiss Army Knife? Picture an iron rod with a saucer on the end—it’s a shovel, a spoon, a back scratcher, AND a canoe scooper all in one! Versatility at it’s finest, and it’s not even our main copper tool in question.
E) “not known to have been used for any task other than canoe making” is like “only canoe making” And that’s been the trend here, the word “only” is our bad guy again. If the tools were used for other tasks, such as building huts, that alone wouldn’t weaken the plausibility of the conclusion drawn in the stimulus. They tools could be used for canoe making AND building huts. The conclusion could still stand as long as at least canoe making was one of the uses.