Supporter/Defender Assumptions and New Info in Conclusion

[Nikki Siclunov]

We recently received the following question:

This is more of a general question in regards to assumption questions and logical reasoning.

In the recent class I took with power score we discussed two types of assumption questions. There are supporter assumptions and defender assumptions. On the information that I gathered, it looked like supporter assumption questions can have new information show up in the conclusion of the stimulus.

And in regards to the defender assumption questions, it seems like there is no new information and the conclusion. That the stimulus discusses the same thing through out. But, in a stimulus that is a supporter assumption, new information can show up in the conclusion.

Is this always the case? Will there always be one type of assumption stimulus that present new information in the conclusion and then another type of assumption stimulus that presents no new information and the conclusion?

Thank you again!!! I'm doing my review before the exam on Saturday, so just wanting to clear up some confusion that I have!

I'm really grateful for your time.

Hi,

Thanks for the question. Let me put it this way: don’t worry too much about the distinction between Supporter and Defender Assumptions. Ultimately, all assumption perform the same exact role in the argument: they must be true for the conclusion of the argument to be logically valid, or else the conclusion would be rendered weak (or invalid). Test makers would only ask us to identify an assumption upon which the argument depends if there was something wrong with the argument: conclusions that are properly and completely justified by the premises don’t make any assumptions. So, if you know why the conclusion does not logically follow from the premises, you’re on the right track to identifying the assumption(s) upon which that conclusion depends, whether Supporter or Defender.

Yes, if the conclusion introduces a new (“rogue”) element, then the author must be assuming that this new element is logically connected to the rest of the argument. In such cases, the correct answer choice is likely to be a “Supporter" assumption that references the rogue element. However, oftentimes the conclusion makes a logical leap without overtly introducing an entirely new idea: a given argument can be weak for many reasons. In such cases, the correct answer choice is likely to perform a Defender role, negating the possibility of a weakness. In the end of the day, however, whether there is or there isn’t a new element in the conclusion is an ancillary question in Assumption questions, as the range of possible assumptions being made can be quite wide, and not all of them will “link” that element back to the premises. Let me give you an example:

Premise: Restaurant X just received a poor rating by one of the country’s foremost restaurant critics.
Conclusion: The quality of the food at Restaurant X must not be good.

The conclusion clearly introduces a new element (food quality) that the author is assuming to be causally related to the poor rating given to the restaurant. Clearly, many of the assumptions made here will fall into the “Supporter” function:

• The quality of the food at a given restaurant can influence what rating the restaurant receives.
  Poor ratings are sometimes given to restaurants serving inferior food.
  Restaurants serving high quality food generally don’t get poor ratings. Etc...

However, the author also makes many other assumptions that have nothing to do with the rogue element in the conclusion:

• The critic in question is able to accurately rate the restaurants that he or she visits.
  The critic in question is not biased by personal dislike of the restaurant’s chef.
  Restaurant ratings are not merely a measurement of the restaurant’s popularity or quality of service. Etc.

As you can see, the second set of assumptions do not “link” the food quality back to the premises, and yet they perform the same function: they establish conditions that must be true for the conclusion to make logical sense. In this particular case, the author is assuming that there was no other reason (except for the food quality) as to why the restaurant received the rating it did. As long as you understand (1) what makes the conclusion potentially suspect, and (2) what an assumption is, from a purely conceptual point of view, you'll be fine. Remember: Each and every assumption upon which a given argument depends is a claim that must be true for the conclusion of that argument to be logically valid. This is precisely why you can always prove the correct Assumption answer: if you negate it (whether it’s a Supporter or a Defender), the conclusion will be rendered invalid. This is the basic rationale behind the Assumption Negation Technique.

Hope this helps! Let me know.