#22 - A book tour will be successful if it is well

[Administrator]

Complete Question Explanation

Parallel Flaw. The correct answer choice is (C)

The conditional statements here lead the author to a unique kind of mistaken conclusion. The first
conditional statement: if a book is well publicized and the author is established, then a book tour will
be successful:

well publicized book tour
+ book tour successful
well established author

Next, we are told that Julia is an established writer and her book tour was successful. Based on the
diagram above, these two pieces of information do not lead to any logical conclusion. However,
the author incorrectly concludes that Julia’s book tour must have been well-publicized. The author
appears to mistakenly think that if any two conditions are met, the third one is met as well.

The question that follows is, not surprisingly, a parallel flaw question, which means that the correct
answer choice will reflect the same mistaken notion—that if one of two sufficient conditions is met,
and the sole necessary condition is met, this must mean that the second sufficient was met as well.

Answer choice (A): This clever wrong answer choice might have been appealing at first, but here we
have two necessary conditions and one sufficient:

This recipe will turn out only if it is followed exactly and high quality ingredients are used:

followed exactly
recipe will turn out +
high quality ingredients

All we need to know is that the recipe turned out in order to logically conclude that high quality
ingredients were used. Since the conclusion here is valid, this choice cannot parallel the flaw.

Answer choice (B): Although this choice does illustrate flawed logic, it is not precisely the same
type. This answer choice presents something that looks almost like a standard mistaken reversal, but
adds an additional error as well:

If a computer has the fastest microprocessor and the most memory available, it will meet Aletha’s
needs this year:

fastest microprocessor available
+ meet Aletha’s needs this year
most memory available

The computer Aletha used met her needs last year, so it must have had the fastest microprocessor and
the most memory available last year:

fastest microprocessor available
met Aletha’s needs last year +
most memory available

Again, this looks almost like a straightforward mistaken reversal, but this statement adds the
additional error of basing a conclusion about last year on a conditional statement about this year.

Answer choice (C): This is the correct answer choice. As prephrased above, this choice provides
a conditional statement with two sufficient conditions and one necessary, making the exact same
mistake as that in the stimulus: If cacti are kept in shade and watered more than twice per week, they
die:

kept in shade
+ die
watered more than twice per week

Based on the fact that a particular cactus was kept in the shade and is now dead, this choice
concludes that it must have been watered more than twice per week. Exactly like the flawed logic
from the stimulus, this choice illogically presumes that meeting one of two sufficient conditions,
along with the necessary condition, will assure that the second sufficient condition was met as well.

Answer choice (D): This incorrect choice might look good at first, because it deals with two
sufficient conditions and one necessary condition. The problem is that it uses valid logic:

A house will suffer from dry rot and poor drainage only if it is built near a high water table:

dry rot
+ built near high water table
poor drainage

This house has suffered from dry rot and poor drainage, so it must have been built near a high water
table. This logic is valid as shown by the diagram above, so it cannot parallel the flawed logic from
the stimulus.

Answer choice (E): Much like incorrect answer choice (D), this choice might have initial appeal
because it presents two sufficient conditions and one necessary. The problem, as with answer choice
(D), is that this answer reflects valid logic. In this choice, we are first told that if you wear a suit with
double vents, and it has narrow lapels, then you will be fashionably dressed:

suit with double vents
+ .....fashionably dressed
suit has narrow lapels

Thus it is valid to conclude that if Joseph was wearing a suit with double vents and narrow lapels that
Joseph must have been fashionably dressed. Since this choice uses valid logic it cannot parallel the
flawed logic found in the stimulus.

[anahi78]

Why is choice C better than A?

[Jacques Lamothe]

Hey anahi78,

The issue with answer choice A is its use of the phrase "only if." While that sounds similar to the standalone "if" used in the stimulus reasoning, the two phrases mean very different things when you are diagramming sentences into formal logic.

The stimulus is:
well publicized AND established writer --> successful book tour
established writer AND successful book tour --> well publicized

Put into symbols:
A+B --> C
B+C --> A

Answer choice A is:
Recipe turns out --> follow exactly AND high quality ingredients
follow exactly AND recipe turns out --> high quality ingredients

Put into symbols:
A --> B + C
B + A --> C

Once written out, you can see how it looks much different than what we see in the stimulus. In contrast, answer choice C follows the reasoning pattern of the stimulus exactly because it also uses "if" instead of "only if."

I hope this makes the difference clear!
Jacques