PrepTest 154

Incorrect. This one is an appealing trap, but nothing in the argument actually relies on this specific explanation for humans' alleged effect on the weather. The phenomenon could have more to do with fewer people driving to work, for one thing. It doesn't have to be industrial activity that's to blame for cloudless weekdays, and the argument never claimed it was.

Incorrect. This might slightly strengthen the argument, but it isn't necessary. According to the stimulus, all naturally-occurring seven-day cycles are too weak to produce these results. So even if they exist in the area studied, they don't affect the data.

Incorrect. Again, this doesn't hurt the argument when negated. There could be some other living organism (plankton, say) affecting weather patterns in a way totally independent of human activity, but this particular phenomenon could still be human-caused even if that's so.

Incorrect. This is too broad. Not everything that affects weather patterns needs to be cyclical in order for this argument to work. But, again, when we narrow down to this particular observed phenomenon, the cause can be cyclical even if not all causes of weather pattern chance are.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
It's cloudier on weekends in industrialized areas, according to a 30-year study. So, humans must be affecting the weather. Natural seven-day cycles are rare, and those that are known are too weak to have such effects.

Answer Anticipation:
This is a strange one, so take it slowly. The conclusion is that humans are affecting the weather (Notice the causality: humans cause the cloudiness cycles). The support for that conclusion is that humans have a seven-day cycle, namely weekdays and weekends, and nature doesn't have powerful enough seven-day cycles to change the weather so dramatically. The biggest thing that stands out here is that the author hasn't considered any alternative explanations for the phenomenon; it must be either cyclical human activity or some natural seven-day cycle, and the natural cycles are ruled out. Sounds a little bit like a fallacy of exclusivity, right? Could there be some cause for the weather patterns besides either human seven-day cycles or natural ones? Expect the right answer, when negated, to imply that there could be.

Answer Explanation:
Finally something we can use, even if it comes strangely worded. Basically, when negated, this answer choice says a result can have a seven-day cycle even if the cause doesn't have a seven-day cycle. So theoretically something not on a weekly cycle (sunspots? tides?) could just be causing clouds to behave as if they are on human weekly schedules. This isn't the most elegant Strengthen with Necessary Premise answer in history, but it's the only one that hurts the argument when negated.

Key Takeaway:
Phew, Strengthen with Necessary Premise questions can get tough, especially towards the end of the section! This one highlights the importance of paying attention to causality. Alternate cause is always one of the best ways to attack a causal argument, so you can anticipate Strengthen with Necessary Premise answers that rule out alternate causes. Therefore, when negated, these answers will rule an alternate cause in, destroying the argument.