Anyone who believes in extraterrestrials believes in UFOs. But the existence of UFOs has been conclusively refuted. T...

Nathan on August 30, 2013


I chose answer 'E'. Why was this wrong and 'A' right.

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Melody on August 31, 2013

Let's take look at the stimulus...

not BUFO ===> not BET

P: not UFO
C: not ET

The stimulus is flawed because it assumes without presenting any evidence, that just because UFOs do not exist, that a belief in extraterrestrials is also false. Remember, the contrapositive of the the principle rule is "If one does not believe in UFOs, then one does not believe in extraterrestrials." We cannot equate this with "If UFOs do not exist, then extraterrestrials do not exist." We have not been given any information as to when a belief in something should be considered the same thing as reality.

(A) is CORRECT because it exactly parallels the flaw in the stimulus.

PR: BU ===> BC
not BC ===> not BU

P: not C
C: not U

Again, just because the contrapositive of the principle rule is true: if one does not believe in centaurs then one does not believe in unicorns, that does not mean that the nonexistence of centaurs is sufficient to conclude the nonexistence of unicorns. We cannot equate the non-belief in something with the nonexistence in something because beliefs and reality are not necessarily the same thing.

(B) is incorrect because it is a valid argument.

PR: BU ===> BC
not BC ===> not BU

P: not BC
C: not BU

This argument is a correct application of the contrapositive.

(C) is incorrect because, while flawed, it does not parallel the flaw in the stimulus.

PR: BU ===> BC
not BC ===> not BU

P: not BU
C: not BC

This is the incorrect contrapositive. Remember to negate AND reverse. DON'T JUST NEGATE! We cannot take the nonexistence of the sufficient condition to conclude the nonexistence of the necessary condition (i.e. just because something is not a carrot, doesn't necessarily mean it is not a vegetable). The flaw in the stimulus is not an incorrect contrapositive, but rather equating non-belief with non-existence.

(D) is incorrect because it does not parallel the stimulus.

PR: BU ===> BC
not BC ===> not BU

P: no good reason to BC
C: BU unjustified as well

We have no evidence to support the argument being made. Just because there is no good reason to believe in centaurs, does not necessarily mean that a belief in unicorns is also unjustified. The principle set forth does not give us any information on when a belief is justified or unjustified.

(E) is incorrect because it does not parallel the stimulus.

PR: BU ===> BC
not BC ===> not BU

P: not U
C: not BC

Though this is similar to the flaw in the stimulus, it is not the "most similar" because unlike the stimulus, (E) is not incorrectly invoking the contrapositive. Here we see the author equating "not U" with "not BU" to conclude "not BC." This is clearly flawed (i.e. don't just negate and "not U" is not the same thing as "not BU") but it is not the same flaw that we encountered in the stimulus.

We are looking for the answer choice that best parallels the stimulus. Therefore, (A) is our correct answer.

Hope that helps! Let me know if you have any other questions!

Nathan on August 31, 2013

Thank you. I am consistently missing key words when reading the stimulus. However, things are improving.