PrepTest 103, Section 1, Question 1
Three-year-old Sara and her playmate Michael are both(49 more words not shown)
The reasoning in the argument(5 more words not shown)
- Apresupposes what it(4 more words not shown)
- Bmistakes the cause(10 more words not shown)
- Cfails to distinguish(16 more words not shown)
- Dtreats evidence that(15 more words not shown)
- Emakes a general(20 more words not shown)
Reading the argument
The kids probably have the same illness. Fine. They have the same symptoms and spend every afternoon together, so that's a reasonable possibility. But two people can have similar symptoms without having the same illness.
That matters when the argument suddenly says Sara definitely doesn't have a streptococcal infection. We know Michael doesn't have one. We don't know that Sara's illness is Michael's illness. Maybe Michael has the flu and Sara has a streptococcal infection. The argument has left that possibility open.
What we’re looking for
We're being asked to identify the flaw. The problem is the jump from “probably” to “definitely.” Even if we're very confident that the children have the same illness, that doesn't justify being certain about Sara's diagnosis.
Working the answers
- A
The argument doesn't start by assuming that Sara has no streptococcal infection. It tries to establish that using Michael's diagnosis and the likelihood that they share an illness. Those reasons don't prove the conclusion, but they are separate reasons. A bad argument isn't automatically an argument that assumes its own conclusion.
- B
Nobody has reversed a cause and its effect. Playing together might help explain why the children have the same illness, but the author doesn't argue that having the same illness caused them to play together. The mistake concerns how certain we can be about Sara.
- C
We're trying to determine whether Sara has a streptococcal infection at all. Distinguishing severe infections from mild ones doesn't fix the missing link between her illness and Michael's. She might have either kind even though he has neither.
- DCorrect
The argument gives us a likely connection between the children's illnesses, then treats that connection as guaranteed. If they had to have the same illness, Michael's diagnosis would settle Sara's. But “probably the same” leaves room for them to have different illnesses, including the possibility that Sara has the infection Michael doesn't have.
- E
The conclusion is about one child, Sara. The author isn't using these two children to make a claim about all children, all playmates, or everyone with these symptoms. An unrepresentative sample would matter to that broader kind of conclusion; it isn't the mistake here.
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