Self-study
Geologist: A new method for forecasting earthquakes has reliably predicted several earthquakes. ██████████████ ████ ██████ ███ ███████ ████ ████ ██ ██████████ ████ ████ █████████ ██████ █ █████ ██ ███ ███ █ ████ ██████ ██ ███ ███████ ██████ █████ █████ █ ██████████ ██ ███ ███ █ ████ ██████ ███ ██ ███ ██████████ ███████ █ ██████████ ███████████ ███████ ███ █ █████ ████ ██████ ████████████ ███████ ███ ███ ██████ ██ ████████ ██ ██ ███████
Summary
The geologist concludes that the earthquake-forecasting method is unlikely to be useful. He supports this by saying that it can only predict that an earthquake will fall somewhere within a range of two and a half points on the Richter scale, and two and a half points can be the difference between a barely noticeable earthquake and one that causes significant damage.
Missing Connection
We know the new method can’t always tell the difference between a barely noticeable earthquake and one that causes significant damage.
The geologist then draws a conclusion about the method’s usefulness, but his premises never address usefulness at all. To get from his premises to his conclusion, he must assume that an earthquake-forecasting method is unlikely to be useful if can’t always tell the difference between a barely noticeable earthquake and one that causes significant damage.
20.
Which one of the following, ██ ████████ ███████ ███ ███████████ ██████████ ██ ██ ████████ █████████
a
Even if an ██████████████████████ ██████ █████ ███████████ ██████ █ ████ ██████ █████ ██ ███ ███████ ██████ ████ ██████ ██ ███ ██████ ██ ██ ██████ ██████ ███ ███████████ ███ █████████
We need to know whether useful methods must be able to tell the difference between barely noticeable earthquakes and ones that cause great damage, not whether useful methods must be reliable. We already know that the new method has reliably predicted several earthquakes.
b
An earthquake-forecasting method ██ ████████ ██ ██ ██████ ██████ ███ ███████████ ██████ █████████████ ███████████ ████ ███ ██████ ██████████ ████ ████ ████ ██████ ██ ███████████ ████████████
The new method’s predictions can’t always differentiate between earthquakes that are barely noticeable and ones that cause great damage. If a method that can’t always differentiate between these things is unlikely to be useful, then the new method is unlikely to be useful.
c
An earthquake-forecasting method ███ ███ ████ █████ ██ ██ ██████ █████ ██ ███ ████ ████ ██ ████████ ███████ █ █████ ██████ ██ ████████████
We know that the new method has reliably predicted at least several earthquakes, but (C) fails to establish that a method that can’t always tell the difference between non-severe and severe earthquakes is unlikely to be useful.
d
Several well-established methods ███ ███████████ ███████████ ███ ███████ ██████ ████ ████████ ██████ ████ ███ ███ █ ████ ██████ ██ ███ ███████ ██████
The geologist’s argument only addresses the new method; the predictions of any other methods are irrelevant. Instead, we need to prove that the new method is indeed unlikely to be useful.
e
An earthquake-forecasting technique, ████ █ █████████ ████████ ████ ████ ████████ ██ ██ ██████ ███ ██ ███ ███████████ █████ ███████████ ███████ ███████████ ████ ███ █████████████ █████ ███ █████ ████ █████ ████████████ ███████
The new method’s prediction range can be the difference between a barely noticeable earthquake and one that causes considerable damage. We don’t know that it never distinguishes between the two. (E) also seems to point to a much greater range, from “imperceptible” to “catastrophic.”