Self-study
So far this summer there has been no rain in the valley. But usually a few inches of rain fall there each summer. Since only one week of summer is left, it will probably rain in the valley within the next week.
18.
The flawed pattern of reasoning in the argument above is most similar to that in which one of the following arguments?
a
Aisha has finished proofreading all but the last two pages of an issue of the journal Periodos and has encountered no errors. However, there are sometimes a few errors in an issue of the journal Periodos. So there may be errors in the pages that Aisha has not yet checked.
No flaw. The premises say that there are sometimes errors in Periodos, and the conclusion states that there may be errors in the last two pages of this issue. Both the premises and conclusion deal with the possibility of errors and never mistake possible errors for likely errors.
b
There are generally few errors in an issue of the journal Periodos. Aisha has finished proofreading all but the last two pages of an issue of this journal but has encountered no errors. Hence, there are probably no errors in the pages that Aisha has not yet checked in this issue of the journal.
Wrong flaw. These premises state that there are usually few (but at least some) errors in Periodos, but it concludes that there will likely not be any errors. Just because Aisha hasn’t encountered errors yet doesn’t mean there won't be any in the next pages, especially since there are sometimes errors in Periodos. This doesn’t match the stimulus because it predicts the probable absence of errors based on a lack of prior errors, while the stimulus predicts probable rain based on a lack of prior rain.
c
On average, there are a few errors in an issue of the journal Periodos. Aisha has finished proofreading all but the last two pages of an issue of this journal but has encountered no errors. So there are probably errors in the pages she has not yet checked in this issue of the journal.
This answer choice confuses possibility with probability. We know that there are usually a few errors in each issue, so there could be errors in this issue. However, concluding that the last two pages of this issue are likely to contain errors is not supported. There could be some underlying reason for this issue’s lack of errors, such as the author proofreading it before submitting it to Aisha, which would mean it is no more likely for the last two pages to contain errors than any other pages in the issue.
d
Aisha has proofread several issues of the journal Periodos and has encountered no errors. But there are seldom any errors in an issue of this journal. So there will probably be no errors in the next issue of the journal Periodos that she proofreads.
No flaw. Aisha’s prior experience proofreading this journal, along with the fact that this journal rarely contains errors, supports the conclusion. The author concludes that it is unlikely, but not certain, that the next issue will contain no errors, which aligns with the premises—they say it is rare for an issue to contain errors, but sometimes it happens. There is no confusion of possibility and probability here.
e
There usually are errors in each issue of the journal Periodos. Since Aisha has finished proofreading the latest issue of this journal and has detected no errors, Aisha has probably made a mistake in her proofreading.
Wrong flaw. This answer choice assumes that there usually being errors in issues of Periodos means that there must have been an error in the issue Aisha proofread. However, just because it is probable that each issue contains an error does not mean it is certain that every issue does. It is possible that this issue was error-free and Aisha did not make a mistake in her proofreading. This is different from the stimulus’s error of assuming that just because something is possible, it is probable.