#22 - All intelligent people are nearsighted. I am very near

[Paul Marsh]

Complete Question Explanation

The correct answer choice is D.

From the stem we know this is a Parallel Flaw question. The correct answer choice will have an argument that contains both of the flaws in our stimulus.

So first, we need to identify the flaws in our stimulus. Luckily, the stimulus is quite short so we don't have to do much digging. The argument in the stimulus clearly is using some conditional reasoning. Whenever conditional reasoning is involved in a Flaw question, we always want to keep a close eye out for Mistaken Reversals/Negations.

Sure enough, the argument here makes a Mistaken Reversal. The first premise gives us the conditional that Intelligent Nearsighted. The second premise tells us that John is very nearsighted. The conclusion switches the order of the conditional, and proclaims that John's nearsightedness is sufficient to say that John is intelligent. So we know that the first Flaw here is that the argument confuses the sufficient and necessary conditions of the conditional in the premise (aka a Mistaken Reversal).

How about the second Flaw? Whenever the conclusion contains a "new" word or phrase (in other words, that word wasn't mentioned in the premises), that ought to catch our attention. Here, "genius" should pop out as it is a brand new word in our conclusion. Did the premises support the conclusion that "I am a genius"? No; even if there wasn't a Mistaken Reversal here, the premises would only definitively support the conclusion of "I am intelligent". So there is some kind of gap here between the "intelligent" in the premises and the "genius" in the conclusion. That gap is the second Flaw in our argument. How exactly should we characterize that gap? I think Nikki did so very nicely in her earlier response, so I am going to re-post what she wrote when she said that this is an issue of "Assumed correlation. Just because nearsightedness is necessary for intelligence does not mean that the two qualities correlate in the way the author assumes that they do. The argument provides no reason to suspect that a higher degree of intelligence correlates with a higher degree of nearsightedness, or vice versa. There is a clear error of an assumed correlation."

So we are looking for an answer choice whose conclusion 1) relies upon a Mistaken Reversal of a conditional in the premises, and 2) assumes correlation between degrees. With that, let's turn to the answer choices.

Answer Choice (A): The author of this answer choice appears pretty down on herself, but she should have a little more confidence in her intelligence! Why? Well, the conclusion of her conclusion actually correctly uses the contrapositive of the conditional in its premise. So her argument has not made a Mistaken Reversal, meaning that this choice is wrong because it does not have the 1st Flaw in common with our stimulus.

Answer Choice (B): The argument in this answer choice does have a conclusion that relies upon a Mistaken Reversal, so it has the 1st Flaw in common with our stimulus. However, the conclusion does not assume correlation between the degrees like the 2nd Flaw that we're looking for. (In fact, it's pretty tough to imagine how it would even do so. "This bird has a giant beak, so therefore it must be a super chicken?")

Answer Choice (C): This is likely the most tempting wrong answer choice, since the conclusion kind of relies upon a Mistaken Reversal of the conditional in the premise, and it does sort of assume correlation between degrees albeit in a very bizarre way. I think we can rule this one out primarily because the part in the conclusion about the size of the spider ("twice as big") isn't really anywhere in the premises, so it isn't just a clean Mistaken Reversal of the conditional in the premises. That and the assumption about degrees is very mathematical in (C) (exactly 2x), whereas in both the stimulus and (D) it's similarly vague.

Answer Choice (D): This is the correct answer. The premise lays out a conditional, and the conclusion relies upon a Mistaken Reversal of it. So (D) matches our first flaw. And it also assumes correlation between degrees - just because he is very happy, he must be very tall. So the argument in (D) uses both Flaws that our stimulus did.

Answer Choice (E): This argument in this answer choice is correctly reasoned; it contains neither of the Flaws from our stimulus.

[destaat]

The answer is D. I see why but why wouldn't B work?

[Steve Stein]

Hi destaat,

This is a great question, because they've managed to include two distinct flaws in one short stimulus, and the question requires you to find the choice that exhibits both.

The first flaw is the classic Mistaken Reversal:
Conditional statement provided:
If you're smart, then you are nearsighted: Smart Nearsighted
Author's flawed conclusion (the Mistaken Reversal of the first statement).
I'm nearsighted, so I must be smart: Nearsighted Smart

The second flaw concerns the matter of degree. The author wrongly assumes proportional increases and decreases based on degree of nearsightedness. The reasoning would have been bad enough with the mistaken conclusion that if you're nearsighted, then you're smart. The author's conclusion goes even beyond this flaw, asserting that the more nearsighted you are, the smarter you are.

Answer choice D replicates both flaws (with the conclusion that goes beyond a simple Mistaken Reversal, adding the presumption of proportional increases: the happier you are, this choice concludes, the taller you are.

Answer choice B is the most popular incorrect answer, because it does provide a Mistaken Reversal, but the second flaw is omitted.

I hope that's helpful! Let me know--thanks!

~Steve

[destaat]

It was thank you.

[mlhousto]

This is the stimulus:

All intelligent people are nearsighted. I am very nearsighted. So I must be a genius.

Which one of the following exhibits both of the logical flaws exhibited in the argument above?

I got the answer right. I picked D because of the over exaggeration of the statement and the incorrect correlation. Extremely happy = extremely tall being parallel to intelligence = genius thought level.

My question is, however, is that I'm uncertain which flaws the book categorizes that my reasoning falls under. I think one of overgeneralization, would the other being cause and effect? Mistaking nearsightedness as a cause for genius level intelligence?

Sorry if this question seems strange, I'm probably over thinking things as per usual, but I just want to make certain that I even though I got the question right, I'm understanding WHY I got it right and recognising key components of the types of weaken questions as well.

[Nikki Siclunov]

Hi mlhousto,

Thanks for your question. There is no evidence of causation in the stimulus. The argument is flawed for two reasons:

1. Conditional reasoning. By saying that all intelligent people are nearsighted, the author posits nearsightedness as a necessary condition for intelligence:

Premise: Intelligent Nearsighted

The conclusion, however, assumes that being nearsighted is sufficient for someone to be intelligent:

Conclusion: Nearsighted Intelligent

Putting aside the exaggerated nature of both attributes in the conclusion, this is a Mistaken Reversal.

2. Assumed correlation. Just because nearsightedness is necessary for intelligence does not mean that the two qualities correlate in the way the author assumes that they do. The argument provides no reason to suspect that a higher degree of intelligence correlates with a higher degree of nearsightedness, or vice versa. There is a clear error of an assumed correlation.

Answer choice (D) parallels both types of logical flaws, and is therefore correct.

Hope this helps!

[mlhousto]

Ah, thanks Nikki! I keep forgetting about conditional reasoning for some reason, probably because I'm the worst at it, but I'll keep working at it. Glad I got the correlation right, though so that's a bonus.

[bella243]

I don't understand how to diagram D. Where does my thinking go wrong?
(D)
John -> extremely happy
Tall people -> happy
Conclusion: John -> extremely tall
In other words: A -> very B
C -> B
Therefore, A -> very C

Stimulus: Intelligent -> nearsighted
very nearsighted -> very intelligent
In other words: A -> B
very B -> very A

[Paul Marsh]

Hi bella 243! Nice job trying to diagram out the conditionals.

However, your diagram is a bit inconsistent in what was diagramed as a conditional vs. what wasn't. For Answer Choice (D), you drew out "John is extremely happy" as a conditional (you wrote, "John extremely happy"). But while diagramming the stimulus you didn't draw out "I am very nearsighted" as a conditional (which, if you wanted to, would be diagrammed as something like: I very nearsighted.

So to be consistent, you want to either diagram both of those statements as conditionals, or neither. If you do want to diagram both of those as conditionals, the stimulus would look like:
Premise 1: Intelligent nearsighted
Premise 2: I very nearsighted
Conclusion: I genius

And Answer Choice (D) would look like:
Premise 1: Tall happy
Premise 2: John extremely happy
Conclusion: John extremely happy

And so (D) still parallels the stimulus and is a good answer choice.

However, I would say that diagramming those two clauses (the second premises listed above) as conditionals is needlessly confusing. Diagramming conditionals is a tool that can often help you parse out the logic used in an argument. But not every sentence that can possibly be written in conditional format necessarily needs to be diagrammed as a conditional! In fact attempting to do so can be counterproductive. While practicing, always being on the lookout for conditionals is a good knack to have. But ask yourself after: how did diagramming that conditional help me to arrive at the answer? If you do that every time, as you progress in your studies you'll develop a sort of instinct about what statements are helpful to draw out the conditional for, and what statements are not. Here, focusing on diagramming "John is extremely happy" as a conditional doesn't do much to help us attack the flawed logic underlying this argument; as you experienced, it can even needlessly distract from the mistaken reversal at play.


With all that out of the way, I want to briefly run through this question from top to bottom. Please also refer to the full explanation I have posted above. Hope that helps!