PrepTest 150, Section 3, Question 8
Of the many works in a collection from(59 more words not shown)
The flawed pattern of reasoning(14 more words not shown)
- AThe city council(43 more words not shown)
- BThe city map(46 more words not shown)
- CI have just(44 more words not shown)
- DOn this city(39 more words not shown)
- EThe legend on(36 more words not shown)
Reading the argument
Two weeks on display tells us the schedule. Does it tell us why?
The most light-sensitive pieces get two weeks, and so do the most valuable pieces. Those facts give us reasons a work would have a short display. They don't say that every other work stays longer. Perhaps some other consideration also limits a work's display to two weeks.
That's my first objection to the conclusion about Spring and Autumn Maples. Knowing that valuable works receive a two-week display doesn't let us identify value from the schedule alone. We haven't established that value is the only possible explanation for that schedule.
What we’re looking for
For the parallel flaw, I'd look for an argument that takes a result associated with a category and assumes that observing the result establishes membership in that category. Keep the distinction between what guarantees the result and what the result actually tells us.
Working the answers
- A
The map will include both existing structures and planned developments. A housing development built decades ago belongs to the existing group, so its not being newly planned doesn't justify excluding it. A overlooks a category the map expressly includes. It doesn't observe a shared marking and wrongly identify which of two categories produced it, as the original identifies value from the display period.
- B
Purple indicates public buildings on the new map; blue did so on the old map. The bank has a blue dot on the new map, whose meaning hasn't been given. B wrongly uses the old color rule to draw a conclusion about the bank's past from its current marking. The problem involves changing conventions over time, not two current categories sharing one result. We can't even assume the current blue dot means the bank is a public building now.
- C
Shearing Street is already known to be a thoroughfare. The map's rule calls for a solid line, but the street has a dotted line, so the author concludes that the mapmakers made a mistake. That starts with the street's identity and checks its marking against the rule. The original goes the other way: it starts with Spring and Autumn Maples' two-week display and infers that the work is especially valuable. C doesn't make that same move from an observed sign to one particular explanation for it.
- D
The two uses of a solid line create possible ambiguity, but D concludes that there is no way to resolve it. Other information, such as where the line lies and the surrounding labels, might distinguish a road from the city boundary. More importantly, D refuses to identify either category, whereas the original confidently selects one category despite another possible explanation.
- ECorrect
Historical monuments and hospitals both receive purple dots. Seeing a purple dot therefore doesn't establish that it marks a hospital; it could mark a historical monument.
This makes the original's problem even more concrete than my initial concern about additional possible reasons. We were already given another reason for a two-week display: sensitivity to light. The painting could get that schedule for sensitivity rather than exceptional value. Map the roles: purple dot is the two-week display, hospital is most valuable, and historical monument is light-sensitive. Both arguments pick one category from a result shared by two.
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