Self-study
Martha's friend, who is very knowledgeable about edible flowers, told Martha that there are no edible daisies, at least not any that are palatable. ███████ ████████ ███████ ████ █████ █████ ███ ███████ ████ ███ █ ████ ██ █████████████ ███ █████ █████ ███ ██████ ██████████████ ████ ███ █████ ██████████ ████ ███ ██████ ████ ███ ████ ██ ██████████
Method of Reasoning
Martha concludes that there are some daisies that are both edible and palatable. Her reasoning is that some chrysanthemums are edible and palatable, and some chrysanthemums are daisies.
Identify and Describe Flaw
We don’t know if there’s any overlap between the subset of chrysanthemums that are edible and palatable and the subset that are daisies. It’s possible that none of the edible and palatable chrysanthemums are also daisies. Therefore, Martha’s inference is invalid.
Consider an analogous argument: Some people who wear masks are bank robbers, and some people who wear masks are nurses. Therefore, some bank robbers are nurses.
20.
Which one of the following ███ █ ██████ ███████ ██ █████████ ████ ████ ████ ██ ████████ ██████████
a
Jeanne is a ██████ ██ ███ ████ ███████ ███ ███ ████ ██████ ██ █████████ ██ ██████ ██ ██ █████████ ███████
This is the wrong flaw. (A) is the cookie-cutter flaw of confusing part and whole: just because the chorus as a whole is renowned, it doesn’t mean that every individual member is renowned. (Furthermore, renown may not be equivalent to excellence.) By contrast, the flaw in the stimulus is the potential lack of overlap between two different subsets of a whole.
b
Rolfe belongs to ███ ███████ ███████ ██████ ███ ███ ███████ ██ ████ █████ ███ ████ ████████ ██ █████ ██ ██ ████ ███████
This is valid reasoning, unlike the stimulus. If all members are members are avid readers, and Rolfe is a member, Rolfe must indeed be an avid reader.
c
Some of Noriko's ███████ ███ ██ ███ ██████ █████ ███ ████ ███████ ██ ███ ██████ ████ ███ ████ █████████ ██ ██ █████ ███ ██ ████████ ███████ ████ ██ █ ████ ████████
(C) concludes that there are some sisters of Noriko that are both debaters and poor students. The reasoning is that some of Noriko’s sisters are debaters, and some debaters are poor students.
This is the same flaw of assuming overlap between subsets that we saw in the stimulus. It’s possible that none of the debaters who are poor students are also Noriko’s sisters.
d
Most of Leon's ███████ ███ ████ █████████ ███ ████ ████████ ███ █████ ███████ ██ ██ ██ ██████ ████ ██ █████ ████ ██ ██████ ███████ ███ █████ ███████
This is valid reasoning, unlike the stimulus. If all good swimmers are strong, and at least some of Leon’s friends are good swimmers, some of Leon’s friends (who are good swimmers) must be strong.
e
Many of Teresa's ██████████ ████ ███████ ██████ ████ ██ ███ █████ ████ ████ ███████ ███ ██ ████ ████████ ██ ████ ██ ████████ ██████████ ███ ████ ████████
This is the wrong flaw. The conclusion of (E) is that some of Teresa’s colleagues are good writers, but the support is that they have written books about good writing. This is an erroneous jump. But it’s not analogous to the stimulus, which mistakenly assumed that different subsets of a whole must overlap.