Marketing agent: A survey of my business clients reveals that, of those who made a profit last year, 90 percent made at least $100,000 in profit for the year. In prior years, not one of these businesses made an annual profit of more than $10,000. So, 90 percent of my business clients increased their profits at least tenfold last year.

Summarize Argument
The marketing agent concludes that 90% of his clients increased their profits at least tenfold last year. He supports this by saying that 90% of his clients who made a profit last year earned at least $100,000, and none of them had earned more than $10,000 in previous years.

Identify and Describe Flaw
The marketing agent concludes that 90% of his clients increased their profit tenfold last year based only on the fact that 90% of his profitable clients did so.

This is the part-to-whole flaw. The agent assumes that what’s true of a subset of his clients applies to all of his clients. But it’s possible that only a few clients were profitable last year, and while 90% of them increased their profits tenfold, most clients didn’t profit at all.

A
overlooks the possibility that the business clients who made more than $100,000 last year made only slightly more than $100,000
This doesn’t impact the agent’s conclusion. Even if these clients made only slightly more than $100,000, they still increased their profits tenfold. Either way, he assumes that what’s true of his profitable clients is also true of all his clients.
B
fails to explain why some of the business clients who made a profit did not increase their profits at least tenfold last year
The agent doesn’t explain why 10% of his profitable clients didn’t increase their profits tenfold, but he doesn’t need to. He only addresses those clients who did increase their profits tenfold, assuming that they’re representative of all his clients.
C
draws a conclusion about all of the business clients from premises about the business clients who made a profit last year
The agent concludes that all his clients increased their profits tenfold last year based on premises about his profitable clients. But what if he only had a few profitable clients? In that case, it’s not true that 90% of his clients increased their profits tenfold.
D
treats conditions that are sufficient for making a profit as though they are necessary for making a profit
This is the cookie-cutter flaw of confusing necessary and sufficient conditions. The marketing agent doesn’t make this mistake; his argument doesn’t rely on conditional logic. Instead, he assumes that what is true of one subset of his clients is also true of all his clients.
E
overlooks the possibility that not all of the business clients made an annual profit of more than $10,000 last year
The marketing agent actually allows for this possibility. 90% of his profitable clients made $100,000, but the other 10% might have made less than $10,000. Also, the clients that were not profitable certainly made less than $10,000 because they didn't make any profit at all.

4 comments

Strengthen

Pretty hard question.

Premises tell us that Shooter Island's waters are exceptionally still and that there are lots of juvenile birds gathered around its waters. There aren't very many juvenile birds in waters in neighboring islands. We have to catch on that we are not told WHY the juveniles are gathering in still waters/Shooter Island. It could be for any number of reasons. The conclusion says that it's because it's their nursery. Okay, that makes sense I guess baby birds like still waters. They're probably using it as a nursery and that's why there are so many juvenile birds there.

If you thought that, then you likely overlooked (C). (C) tells us that whenever possible, waterbirds use still water as nurseries. We think... don't we already know that? Nope, we don't. This is a really powerful assumption that if established, would do wonders for the argument.

(C) tells us waterbird's preference is to use still waters for nurseries whenever it's possible. The stimulus tells us that there are in fact an overabundance of juveniles in still waters. You put the two statements together and now we're pretty sure that they're actually there because they're using it as a nursery and not for some other reason. Our argument is made much better.

(D) is an attractive trap. It says that the waters around the other islands are MUCH rougher. This seems like new information but it hardly is. We already knew from the premises that Shooter Island water is EXCEPTIONALLY still. Not just kind of still. It's exceptionally still. So even if the neighboring waters are a little bit rough, they're MUCH rougher than exceptionally still.

But let's just say that the waters in the neighboring islands are truly objectively rough. Okay, we still don't know why juvenile birds are gathering in still waters/Shooter Island. Is it as the conclusion says that it's because this is their nursery? Maybe. Or maybe it's for some other reason. That means the argument was as strong/weak as it ever was. We didn't do our job of strengthening the argument.


27 comments

The waters surrounding Shooter’s Island have long been a dumping ground for ruined ships and boats, and the wreckage there has caused these waters to be exceptionally still. An ornithologist found that the overall abundance of waterbirds around Shooter’s Island is similar to that around each of the neighboring islands, but that juvenile waterbirds are much more abundant around Shooter’s Island than around those other islands. This suggests that the still waters around Shooter’s Island serve as a nursery for the juveniles.

Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes the abnormally still waters surrounding Shooter’s Island act like a nursery for juvenile waterbirds. Why? Because those waters have roughly as many total waterbirds as waters around nearby islands, but many more juvenile waterbirds.

Notable Assumptions
The author assumes there’s a higher proportion of juvenile waterbirds around Shooter’s Island because the still waters act as a nursery, and not for some other reason. This means assuming adult waterbirds prefer to raise their young in still waters, perhaps because still waters offer some benefit to the development of juvenile waterbirds.

A
The ruined ships and boats around Shooter’s Island have been there for decades.
This is irrelevant. It doesn’t say the ruined ships and boats make life any easier for juvenile waterbirds.
B
The number of juvenile waterbirds around Shooter’s Island, as well as the number around each neighboring island, does not fluctuate dramatically throughout the year.
This establishes that Shooter’s Island is surrounded by an unusually large proportion of juvenile waterbirds throughout the year, but it doesn’t favor the author’s hypothesis. It gives no reason to identify still waters as the cause of that juvenile presence.
C
Waterbirds use still waters as nurseries for juveniles whenever possible.
This makes concrete the author’s assumption that adult waterbirds prefer to raise their young in still waters. It’s a reason to single out still waters as the cause of the juvenile waterbird presence around Shooter’s Island.
D
The waters around the islands neighboring Shooter’s Island are much rougher than the waters around Shooter’s Island.
This offers detail, but doesn’t favor the author’s hypothesis. It doesn’t say juvenile waterbirds prefer still waters to rough waters—it just confirms that the waters around Shooter’s Island are, in fact, exceptionally still.
E
Waterbirds are typically much more abundant in areas that serve as nurseries for juvenile waterbirds than in areas that do not.
This weakens the argument. Since waterbirds in general are no more abundant around Shooter’s Island, it suggests waters around Shooter’s Island are probably not a nursery for them.

Further Explanation

Pretty hard question.

Premises tell us that Shooter Island's waters are exceptionally still and that there are lots of juvenile birds gathered around its waters. There aren't very many juvenile birds in waters in neighboring islands. We have to catch on that we are not told WHY the juveniles are gathering in still waters/Shooter Island. It could be for any number of reasons. The conclusion says that it's because it's their nursery. Okay, that makes sense I guess baby birds like still waters. They're probably using it as a nursery and that's why there are so many juvenile birds there.

If you thought that, then you likely overlooked (C). (C) tells us that whenever possible, waterbirds use still water as nurseries. We think... don't we already know that? Nope, we don't. This is a really powerful assumption that if established, would do wonders for the argument.

(C) tells us waterbird's preference is to use still waters for nurseries whenever it's possible. The stimulus tells us that there are in fact an overabundance of juveniles in still waters. You put the two statements together and now we're pretty sure that they're actually there because they're using it as a nursery and not for some other reason. Our argument is made much better.

(D) is an attractive trap. It says that the waters around the other islands are MUCH rougher. This seems like new information but it hardly is. We already knew from the premises that Shooter Island water is EXCEPTIONALLY still. Not just kind of still. It's exceptionally still. So even if the neighboring waters are a little bit rough, they're MUCH rougher than exceptionally still.

But let's just say that the waters in the neighboring islands are truly objectively rough. Okay, we still don't know why juvenile birds are gathering in still waters/Shooter Island. Is it as the conclusion says that it's because this is their nursery? Maybe. Or maybe it's for some other reason. That means the argument was as strong/weak as it ever was. We didn't do our job of strengthening the argument.


30 comments

Pundit: Clearly, the two major political parties in this city have become sharply divided on the issues. In the last four elections, for example, the parties were separated by less than 1 percent of the vote.

Summarize Argument
The pundit concludes that the two major political parties in the city have become sharply divided on issues. He supports this by noting that in the last four elections, the parties were separated by less than 1% of the vote.

Identify and Describe Flaw
The pundit concludes that the parties are sharply divided simply because they were separated by less than 1% of the vote in recent elections. He assumes that a close vote indicates a sharp division but doesn’t provide evidence for this. It's possible that the close vote actually shows that the two parties have very similar views and are united.

A
confuses the cause of the sharp division with an effect of the sharp division
The pundit actually doesn’t address any causes or effects of the sharp division, so he can’t be confusing the two. Instead, he simply argues that the close vote is evidence of a sharp division.
B
presumes, without argument, that sharp division is a bad thing
The pundit assumes that a close vote is evidence of sharp division, but he never claims or assumes that sharp division is a bad thing.
C
has a conclusion that is merely a restatement of one of its premises
This is the cookie-cutter flaw of circular reasoning. The pundit doesn’t make this mistake. His premise doesn’t support his conclusion very well, but the two are distinct from one another.
D
fails to indicate how what is happening in one city compares with what is happening in other cities
The pundit is only addressing the two major political parties “in this city.” How the elections in this city compare to the elections in other cities is irrelevant.
E
takes for granted that an almost even division in votes indicates a sharp division on issues
The pundit assumes that a close vote indicates a sharp division on issues, but he gives no evidence to support this assumption. It’s possible that an almost even division in votes actually indicates that the two parties are united.

5 comments