#19 - Some species of tarantula make good pets. However

[Administrator]

Please post your questions below!

[sodomojo]

I see why (A) is correct, but I am having trouble dismissing (C).

I have (C) diagrammed as:
P: Regular meter Poetry written by Strawn
P: Poetry written by Strawn ~ Collection
C: Collection ~ Regular meter

To me, combining the first two premises via Poetry written by Strawn would properly lead to the conclusion, because you'd get Regular meter ~ Collection.

Is the issue here that you cannot reverse the above inference into the Collection ~ Regular meter that (C) actually concludes?

[mattnj]

Would appreciate some detail here! Thank you.

[James Finch]

Hi Matt and Sodomojo,

As a Parallel Reasoning question type, let's start with the reasoning found in the stimulus itself:

Tarantulas Good Pets

Poison Fangs Good Pets

and the contrapositive:

Good Pets Poison Fangs

Combine the two premises and we get the conclusion:

Tarantulas Good Pets Poison Fangs

This is valid conditional reasoning. So now that we know what we're looking for, let's look at the answer choices:

(A): We have the following reasoning:

Collection RM

and

Strawn RM, thus RM Strawn

Combined, the premises yield the conclusion:

Collection RM Strawn

This exactly parallels the reasoning in the stimulus, and is the correct answer.

(B): The reasoning is as follows:

Collection RM, thus RM Collection

and

Strawn RM, or RM Strawn

However, because of the two "some" conditionals, we cannot logically infer the conclusion, that

Strawn Collection, because we don't know that the collection did not include all of the poems written by Strawn, both with either regular meter or without.

(C): This answer choice diagrams out to:

Strawn RM

and

Collection Strawn

and it concludes

Collection RM

The problem is clear: there is no logical way to link the two premises to create the inference needed to draw the conclusion, so the logic is flawed, as it is based on a Mistaken Negation of the first premise. This does not parallel our stimulus, so it is incorrect.

(D): Here we have:

Collection Strawn

and

Collection RM

therefore

Strawn's unpublished poetry RM

This answer choice relies on an assumption that the only poetry Strawn has published is in this collection. Unfortunately, we don't know that assumption to be true, and cannot draw the conclusion. More importantly, this is not a parallel to the stimulus, so it is a wrong answer choice.

(E): And finally, this answer choice says:

Collection RM

and

Collection Strawn

and concludes

Strawn RM

The conclusion here again doesn't follow, as we cannot logically chain the two conditional statements, and all we know is what is not in the collection of poetry. We cannot draw any conclusions about Strawn, so this is an incorrect answer choice.

Hope this clears things up!

[mattnj]

Thanks, James, it does.

[MikeJones]

Hi Matt and Sodomojo,

(C): This answer choice diagrams out to:

Strawn RM

and

Collection Strawn

and it concludes

Collection RM

The problem is clear: there is no logical way to link the two premises to create the inference needed to draw the conclusion, so the logic is flawed, as it is based on a Mistaken Negation of the first premise. This does not parallel our stimulus, so it is incorrect.

Hope this clears things up!

Hi. I'm curious as to what the Mistaken Negation is here.

This is how I diagrammed it:

PS some RM
TC /PS

RM some PS /TC

TC some /RM
or
RM some /TC

Where's the problem?

[James Finch]

Hi Mike,

"Some" and "most" are signifiers of formal logic (FL), and not conditional reasoning
(CR). While they may be strung together, formal logic does not follow the same rules as conditional reasoning--one cannot logically negate a formal logic statement in the same way that one can infer the contrapositive from a conditional statement.

Negating the Strawn RM statement is not possible, because of the inherent uncertainty of "some"--it could mean anything from a single instance to all of the poet's works. Thus we have to connect the statement that we are given, in its positive form, with the conditional statement Collection Strawn, to come up with Collection RM, which is not logically possible because of the inability to connect the conditional statement to the formal logic one.

Hope that clears things up!

[harvoolio]

This question hurt me for two reasons: (1) I got it wrong (chose C) and (2) I sunk too much time in this leading to later wrong answers.

Assuming the formal logic escapes me, could I apply some of the Logical Reasoning Bible to eliminate as follows:

(B) Eliminate two some's - stimulus has one.
(D) Eliminate because of different conclusion of only versus some.
(E) Eliminate because of two none's - stimulus has one.

Guess between (A) and (C) and move on. Thanks.

[Adam Tyson]

Absoutely, harvoolio! That process of "Doubling the Conclusion" and "Doubling the Premises" is a huge help here, getting you down to two contenders quickly! From there, you can guess and move on, or you could diagram the stimulus and then diagram one of your contenders. If the diagrams match, you have the right answer; if they don't, pick the other contender!

Well done - that's the way to move through Parallel Reasoning questions faster and with great accuracy and confidence, even when they are fairly complex.