Critical Reasoning

Guidebook writer: I have visited hotels throughout the country and have noticed that in those built before 1930 the quality of the original carpentry work is generally superior to that in hotels build afterwards. Clearly carpenters working on hotels before 1930 typically worked with more skill, car, and effort than carpenters who have worked on hotels build subsequently.

Which of the following, if true, most seriously weakens the guidebooks writer's argument?

(A) The quality of original carpentry in hotels is general far superior to the quality of carpentry in other structures, such as houses and stores.
(B) Hotels build since 1930 can generally accommodate more guests than those build before 1930.
(C) The materials available to carpenters working before 1930 were not significantly different in quality from the materials available to carpenters working after 1930.
(D) The better the quality of original carpentry in a building, the less likely that building is to fall into disuse and be demolished.
(E) The average length of apprenticeship for carpenters has declines significantly since 1930.

OA: D

This is a tough question indeed and many will commit mistakes in such question If any new question of this type will take them with surprise.

Is it a case of formal logic and are we supposed to expertise the formal logic.

The way to get the right answer to this one is to pay close attention to what the argument is saying, and assuming.

Premise: Carpentry in visited hotels built before 1930 is generally higher in quality than that in visited hotels built after 1930.

Conclusion: Carpenters worked with more skill, care and effort before 1930 than they did after 1930.

The conclusion assumes that there is no possible other explanation, as if the difference in quality can only be explained by difference in the skill, care and effort of carpenters working before 1930.

Question: Which most seriously weakens the argument?

Probably we will find an alternate explanation for the difference in quality. Let's go to the answer choices and see what we get.

(A) This says that generally the quality of carpentry in hotels is higher in quality that the carpentry in other structures, which adds absolutely nothing to an argument about why the quality of hotels built at one time is higher than that of hotels built later.

(B) This is a trap answer. It's like a canvass for a person to paint a picture on, a picture explaining why this answer matters, but really the fact that hotels can accommodate more guests changes nothing. You could paint a picture and explain that somehow building bigger hotels causes carpenters to build differently, but really there is no logic supporting that in the information given. It's conceivable that carpenters building bigger hotels would care more, because the projects are more significant, or care less, because there are more carpenters working, and so each one feels less significant that he or she would working on a smaller project.

Painting pictures like those is not the way to get the right answer to a CR question. You can come to reasonable conclusions, but you can't make up basically unsupported stories.

(C) This is another trap answer. In eliminating a difference between building before 1930 and building after 1930, it seems to confirm that the carpenters must have been different, but the difference eliminated is just one of many possible factors that could explain the different levels of quality.

(D) This answer choice may look unrelated to the argument at first, but often seemingly unrelated answers turn out to be the right answer. So saying, "I don't see how this is related" is not necessarily a good way to eliminate answer choices.

While this answer choice doesn't relate to how carpenters work, it does offer an alternative explanation. The currently standing buildings built before 1930 are only some of the ones built in that time period. Others were demolished, and generally the higher quality ones are the ones still standing. So carpentry may not have been generally better before 1930. Rather the lower quality carpentry done before 1930 no longer exists. So the guidebook writer is comparing what are generally the best of the buildings built before 1930 with all of the buildings, high quality and lower quality, that were built later.

The existence of this clearly plausible alternate explanation for the difference in quality significantly weakens the argument.

(E) If anything this might strengthen the argument, as it seems to indicate, though it does not necessarily, that carpenters have indeed become less skilled since 1930.

The correct answer is D.