#16 - Anyone who believes in extraterrestrials believes in

[jonwg5121]

Why can the answer choice not be (B) then?

Does it not follow
"anyone who believes in unicorns believes in centaurs"
unicorn --> centaur
"But you do not believe in centaurs, so you do not believe in unicorns either"
not centaur --> not unicorn

Also why would choice (D) not work?

Thanks!

[Steve Stein]

Hi Jon,

Let's take a look at the reasoning in this stimulus:

Anyone who believes in E.T.s believes in UFOs: Believe in ETs Believe in UFOs

And the contrapositive: NOT Believe in UFOs NOT Believe in ETs

Instead of drawing the valid contrapositive above, the author makes a subtle but important mistake: based on the premise that belief in UFOs is apparently mistaken, the author draws the flawed conclusion that a belief in ETs is mistaken as well:

Author's flawed argument:
Believe in ETs Believe in UFOs
Belief in UFOs is mistaken Belief in ETs is mistaken

Correct answer choice (A) reflects the same flawed reasoning:
Believe in unicorns believe in centaurs
Belief in centaurs is mistaken belief in unicorns is mistaken

Answer choice (B), however, does not make the same mistake in logic, as it presents a valid contrapositive:

Believe in unicorns believe in centaurs
NOT believe in centaurs NOT believe in unicorns

Since this is not flawed logic, it cannot parallel the flaw reflected in the stimulus.

I hope that's helpful! Please let me know whether this is clear--thanks!

~Steve

[jcrodriguez1302]

Could you please explain why answer choice "E" is incorrect?

[fannyfoo92]

I chose answer choice E for this problem and I'm still not convinced that A is the correct answer. The stimulus states that if something hasn't been proven the belief in the other thing is wrong as well. BUT A talks about there not being unicorns at all, rather than there not being a belief in unicorns. Help

[Robert Carroll]

jc,

The stimulus proceeds by presenting a conditional:

believes in ETs believes in UFOs

It then claims that the existence of UFOs has been conclusively refuted. Thus, the thing believed in the necessary condition of the conditional above does not exist.

It then concludes that belief in ETs is false as well.

The stimulus is a flawed argument - the evidence about UFOs really has nothing to do with ETs, so the fact that one belief in false really says nothing about the truth or falsity of the other belief. Since this is a Parallel Flaw question, you must choose an answer that itself contains flawed reasoning, but not just any flaw will do - you must parallel the (bad!) reasoning in the stimulus. The general pattern of that is as follows:

Premise: Belief A Belief B

Premise: Belief B (belief in the necessary condition) is mistaken

Conclusion: So, belief A (belief in the sufficient condition) is mistaken.

Answer choice (E) attempts to claim that the fact that belief in the sufficient condition is mistaken allows one to conclude that belief in the necessary condition is also mistaken. This does not follow the pattern in the stimulus, because the premise is about the wrong condition, and so is the conclusion.

Robert Carroll

[Robert Carroll]

fanny,

I think my discussion here will be helpful:

http://forum.powerscore.com/lsat/viewto ... 046#p19046

However, it may not completely answer your question, so I will elaborate here. The first sentence of the stimulus links one belief with another, making belief in ETs sufficient to make belief in UFOs necessary. The second sentence claims that the object of belief in the necessary condition has been proven not to exist. The conclusion then claims that "belief in ETs is false". This does not mean that the belief doesn't exist; it means the belief is false, so the object of the belief must not exist. Thus, answer choice (A) is the correct parallel.

Robert Carroll

[oli_oops]

Hi Reop,

Thanks for the question.

The phrasing in D indicates that "there is no good reason to believe". This is not as closely equivalent to the stimuli, which indicates that a belief has been "conclusively refuted". The original version is much more certain and definite, whereas the answer choice reads more like an opinion. Answer choice A says "it has been demonstrated", which is closer to "conclusively refuted". Both indicate actual proof.

Answer choice A actually uses the term "belief", so I'm not sure I'm following the argument that it deals with phenomena, rather than beliefs.

Hope this helps!

Beth

Hi Beth,

Thanks for your explanation. Though I have the same questions as well and I don't think you addressed it,
In the Question stem, it said "the existence of UFOs has been conclusively refuted. Therefore a belief in extraterrestrials is false as well"
I think the person I quoted was trying to ask:
In the question stem, ~existence of UFOs ---> ~*belief* in extraterrestrials
HOWEVER, in answer choice A), it was ~centaurs ----> ~unicorns (INSTEAD OF the *belief in unicorns*)
I think that's what he/she meant by necessary condition was a belief, instead of a phenomenon.
That's why I chose D instead of A as well.

If you could explain again that would be great!!

Thanks,
oli

[Robert Carroll]

oli,

Only the first sentence of the stimulus is really about belief. The conclusion says "belief in ETs is false." Does this mean no one believes in ETs? Of course not. It means that a belief in ETs would be a false belief, so if anyone does believe that, that person is believing a thing that is false. In other words, because a belief that ETs exist is a false belief, ETs don't exist.

The first sentence of the premise is thus the only one that's "really" about belief. The conclusion uses the word "belief" while trying to make a statement about the EXISTENCE of something.

Robert Carroll

[Leela]

I diagrammed the stimulus as:

believe in ET --> believe in UFO

UFO existence refuted --> don't believe in ET

Is the reason A is correct, rather than B, because it includes the demonstration of no centaurs, rather than lack of belief in centaurs, similar to the refuted existence of UFOs? I'm not seeing anything else distinguishable between those two answer choices.

[Brook Miscoski]

Leela,

The stimulus shows that everyone who believes in extraterrestrials has a false belief about UFOs, but that doesn't prove that extraterrestrials don't exist. You need to find a similar flaw.

The proper logic is: Believe ET Believe UFO False Belief UFO. Full stop.
The stimulus goes a step further, equating a resulting false belief with the falsity of the original belief.

The contrapositive you have written out isn't used by the stimulus, and you need to be careful since it isn't correct. The contrapositive of the information in the stimulus is:

Not Believe UFO Not Believe ET.

You could argue that the stimulus is making the error of replacing the "not" with "false," but I think it's easier not to do that.

Looking at (A), we have an original belief (unicorns) that is associated with a second belief (centaurs), and the second belief is false. (A) then concludes that the first belief must also be false, the same as the stimulus.

(B) cannot be correct because it does not involve the step of finding either belief to be false, so it leaves out a step. Also, (B) does not have a flaw. It is correct conditional reasoning.