Self-study
Support Anatomical bilateral symmetry is a common trait. ██ ████████ ██████████ ████ ██ ███████ ████████ ██████████ ██ ██████████ █████ ████ ██ █████████ ████████ ███ ███ ██████ ████ ███████████ ██ █████ ███ ██ ███████
Structure: Phenomenon-Hypothesis
We're told about a phenomenon: the trait of "anatomical bilateral symmetry" — let's call it ABS — is common. The argument explains this phenomenon with the hypothesis that ABS must give organisms a survival advantage. As support, the argument claims that if ABS did not confer such advantages, it would not be common.
Analysis: Parallel Reasoning
Let's follow the logical flow of the argument. The stimulus starts by saying that ABS is common, and, therefore, must confer survival advantages on organisms:
common → confer advantages
As support ("after all"), the argument claims that if ABS did not provide such advantages, it would not be common:
/confer advantages → /common
Notice that this is just the contrapositive of what we already diagrammed above. This might make it seem like the "after all" statement isn't so much a new piece of evidence in support of the conclusion as just a restatement of the logic the argument already takes for granted. To see why this argument isn't actually circular, think of it this way:
P1 (the "after all" statement): if ABS did not confer survival advantages, it would not be common.
P2: But ABS is common.
C: Therefore, ABS must confer survival advantages.
We're looking for an argument that follows a similar structure: if /B, then /A. But A is actually true, so B must also be true.
22.
The pattern of reasoning in █████ ███ ██ ███ █████████ █████████ ██ ████ ███████ ██ ████ ██ ███ ████████ ██████
a
Since it is ██████ ███ ██ ███████████ ███ ███ ████ ███████████ ██ ████ ██ ████ ████ ███ ████ █████ ███ ██████ ██████████ █████ ████ ██ ██████ ███ ███ ████ ██████████ ███ ████ █████ ████ ████████ ████ ███ ████████████ ██ █████████
Incorrect. The structure of the first sentence is:
Sawyer negotiating → city takes matter seriously
The next statement, given in support of the conclusion, can be diagrammed as:
/Sawyer available → city defers
These two statements don't follow the "contrapositive"-style argument we saw in the stimulus, so (A) isn't what we're looking for.
b
Clearly, no candidate ██ ██████ █████████ ███ ███ ███ ████ █████████ ██ █████ ████ ██ ███████ ████ █████ █████ ██ █ ████ ██████ █████████ █████████ █████ ██████ ██ █████ ███ ████ ████ ████████ ██ █████
Incorrect. (B) doesn't even follow a clear conditional structure.
c
If Powell lacked ████████ ███████████ ███████ ███ █████ ███ ████ ████ █████████ ██████████ ██ ████ █████ ██ ████████ ██████ ███ ██ ███ █████████ ███████████ ██ ███ ███████████ ██████ ████ ██████████ ████████████████ █████ ██ ██ █████████
Correct. The first sentence diagrams to:
/Powell has skills → /appointed arbitrator
Then we're told that Powell has been appointed arbitrator, so she must have the necessary negotiating skills:
appointed arbitrator → Powell has skills
This follows a structure parallel to the argument in the stimulus, where a counterfactual "contrapositive" (/B → /A) is used to justify the conclusion that since A is actually true, B must also be true.
d
Since Varga was ████ ██ ████████ ██ ███ █████ ██ ████ ████ ████ ██████ ███ █████████ ███ ██████ █████████████ ███ █████ ████████ █████ ██████ ██████ ███ ██████ █████ ████ ███ ███████████ ██████ █████ ██ ████████████
Incorrect. (D) argues that since Varga was away, Rivers must have conducted the negotiations:
Varga away → Rivers conducted
In support, we're told that "Rivers never does the negotiating unless Varga is unavailable." Notice that this translates to:
Varga available → /Rivers conducted
And, by the contrapositive: Rivers conducted → /Varga available
This doesn't actually support the conclusion. The argument makes a sufficiency/necessity confusion to get to the conclusion. So (D) is a flawed argument that doesn't match the structure of the stimulus.
e
If Wong is █████████ ███████████ █ ████████ ████ ██ ███████ █████████ █████ ██ █████ ██ ██████ ██ ███████ ██████ █████ ████ ████ ██ ███████████ █ ██████ ████████ ███ ██████████ ██ █████████
Incorrect. (E) starts with a conditional rule:
Wong appointed → prompt decision
We're then told that since the sufficient condition will likely be met (Wong will probably be appointed), the expected result will probably follow: we can reasonably expect a prompt decision. This is a different structure from what we saw in the stimulus.