A study of 30 years of weather pattern records of several industrialized urban areas found that weekend days tend to ...

shunhe on July 17, 2020

Hi @fable,

Thanks for the question! So let’s recap the stimulus first to make sure we understand the argument. Basically, some study found out that weekend days are cloudier than weekdays. And that means, concludes the author, that human activity has appreciable large-scale effects on weather. Why? Because the few seven-day cycles that occur naturally can’t make any difference in weather patterns. So the argument looks something like

Premise: Weekend days are cloudier than weekdays
Premise: Seven-day natural cycles can’t make any difference in weather patterns
Conclusion: Humans have appreciable, large-scale effects on weather

So now we’re asked for a necessary assumption of the argument. Let’s take a look at (E): if a weather pattern with a natural cause has a seven-day cycle, then that cause has a seven-day cycle. And looking at the argument, that is what’s assumed. What’s the argument saying? Well, basically, that since these seven-day natural cycles can’t make any difference in weather patterns, it has to be humans! But why can’t it be five-day natural cycles, or one day things, or month-long cycles? There’s an implicit assumption here: that if the weather pattern has a seven-day cycle, and it’s caused by something natural, then the cause has to have a seven-day cycle too. After we know that, and we know that none of the seven-day cycles can change weather patterns, then it can’t be a natural cause and so it has to be humans.

And of course, let’s say we negate (E). That means that it could be possible that a weather pattern has a seven-day cycle, and a natural cause, but the natural cause doesn’t have to have a seven-day cycle. Well, that weakens the argument, because the argument only says that it can’t be a seven-day natural cycle. But again, cycles of other lengths could potentially explain the study in that case, and that would mean that natural causes could be the explanation instead of humans, which would weaken the argument.

Hope this helps! Feel free to ask any other questions that you might have.