Assumption Question

[yugal_kishore]

Hi

Referring to the problem -

*text of question and answer choices removed due to copyright (for those wanting a look at the question, it's in LRB Chapter 11, Page 374, q4)

I want to check my understanding whether I have confused myself or I am not understanding the explanation correctly.
Mapping the options A and D based on conditional reasoning.

A) Elevation of mood ----------------> increased level of serotonin
D) Increased level of serotonin ---------> Elevation of mood

Increased level of serotonin - is necessary in the first and sufficient in second. But per your earlier explanation of assumption question -

The stem never uses the word “if” or any other sufficient condition indicator.
.

Also,

Reading through the book in earlier chapters -

1. 'Justify the conclusion' - correct answer is sufficient to prove the conclusion
2. Assumption - correct answer is necessary to prove the conclusion


Now to me, the answer explanation and the aforementioned statements appear contradictory. Please can you help me understand this.


Regards
Yugal

[Adam Tyson]

Thanks for the question, Yugal. I'm not sure what contradiction you are seeing here - can you elaborate?

The stimulus tells us a few things about amino acids, insulin, tryptophan, sugars and seratonin. After telling us that sugar helps seratonin get into the brain, the author concludes that sugar plays a major role in mood elevation and relaxation. Nowhere else in the stimulus is anything mentioned about moods, which means this argument has a logical "gap" in it, a hole in between the premises and the conclusion. The stem asks us to identify an assumption of the argument.

When we see an obvious gap like this one, the assumption answer must do something to close that gap. It must link the premises (sugar, seratonin, etc.) to the conclusion (mood and relaxation). Two of our answer choices do that, as you found, and you have diagrammed them both correctly.

Now, as you read in the LR Bible, an Assumption answer is necessary when the conclusion is true. That is, the conclusion, if valid, proves the answer is true. So we need to pick an answer that MUST be true if the conclusion is true. That is, if sugars really do play a major role in mood elevation and relaxation, then one of these two answer choices is required to be true. Not just one part of the answer, but the whole answer, the whole conditional relationship. I think perhaps you were focusing on the necessary condition in the answer choices, rather than on the entire relationship in the answers?

It is not necessary for mood elevation to require seratonin in order for our conclusion to be true. There could be many other ways to elevate mood and increase relaxation without seratonin being involved. What we need is for seratonin to be sufficient for mood elevation, as shown in answer D.

One more way to approach this is by using the Assumption Negation Technique. Since there is a conditional relationship between the conclusion and the answer choice, with the conclusion (sugar plays a major role in mood elevation and relaxation) being sufficient for the answer, the contrapositive of that relationship must also be true. If you negate the answer choice, it should destroy the argument. In other words, if the answer is false, the argument is false. When you negate answer A, you get "elevation of mood doesn't require seratonin". Does that mean that we now have no evidence that sugar promotes mood elevation through its relationship with seratonin? Nope! Just because it wasn't required doesn't mean it wasn't good enough to do the job. I don't require a hamburger to ease my hunger pains, but eating one will get the job done.

Negating answer D, however, does major damage to the argument. There, we get "seratonin doesn't promote relaxation". If that's the case, then the fact that sugar promotes seratonin would be insufficient to show any connection between sugar and relaxation. With no evidence to link the two, the argument falls apart. That proves answer D to be what we needed.

I hope that explanation made sense and that you can see the difference between what was necessary for the conclusion and what was merely a necessary condition within the answer choice. Don't get those two mixed up!