PrepTest 117, Section 2, Question 1
The tidal range at a particular location is(65 more words not shown)
Which one of the following(9 more words not shown)
- AIt gives only(6 more words not shown)
- BIt fails to(19 more words not shown)
- CIt does not(16 more words not shown)
- DIt presumes, without(18 more words not shown)
- EIt does not(15 more words not shown)
Reading the argument
Gravity makes the tides happen. Does that tell us everything about how far the water rises and falls?
The passage defines tidal range for us: the difference between the height at high tide and the height at low tide. In the Bay of Fundy, that difference can exceed seventeen meters. That's a large change, but we don't need to know anything about this bay to follow the argument.
Let's accept that the sun's and moon's gravity are the only forces inducing the tides. The author then claims that gravity must also explain the entire size of the tidal range. Wait. Causing the movement and determining the size of that movement aren't necessarily the same job. Could something about the location also matter?
What we’re looking for
Perhaps the shoreline or erosion affects the result. I don't know whether either actually does, and we shouldn't treat that guess as a fact about tides. The question is whether the author has ruled out anything beyond gravity affecting the range. The premise doesn't do that. For the flaw question, look for this jump from what produces tides to what fully explains their size.
Working the answers
- A
Adding more examples of tidal ranges wouldn't fix the jump. We could list twenty bays and still need to explain why the force that induces tides is the only thing affecting their range. The problem concerns the connection between the premise and conclusion, not the number of places named.
- BCorrect
The 'conditions in which gravitational forces act' are features of the situation where gravity produces its effect. That wording is abstract, but it captures the concern: gravity could induce tides while the surrounding conditions help determine how large the range becomes. We don't need to establish precisely which condition matters. Failing to consider that possibility makes the claim that gravity explains everything unsupported.
- C
How we measure the two heights doesn't identify the missing connection. The argument concerns what determines the size of the range, not whether we use a ruler or some other measuring method. Nothing given here shows a measurement problem that undermines that reasoning.
- D
Most ocean activity? The author never claims that. The premise concerns the forces inducing tides. Ocean activity is a much broader category, and we aren't told that tides make up most of it. D attributes a sweeping assumption to the argument instead of identifying its actual leap.
- E
Both gravitational effects are already included in the proposed explanation. The author needn't separate the sun's contribution from the moon's to claim that their combined gravity explains the range. Our concern is whether something besides those forces also affects the result.
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