Necessary Assumption v. Strengthen

[uhdang]

Hi, I have a question regarding a distinction between Necessary Assumption and Strengthen Question.

As I understand that the right answer choice for a strengthening question solidifies the argument in multiple ways. One of the ways is to eliminate a possible assertion that would undermine the conclusion.

I find this "possible assertion" very similar to assumptions that I could see from Necessary Assumption Questions. And the right answer choice for this ALSO seems to eliminate possible scenario that would undermine the conclusion. (Some have referred this type of Assumption as "Defender" type or "Shield."

I have been trying to pinpoint and clarify their differences.

So far, my take is that Strengthening choice sounds a bit more general than Necessary Assumption choice. How do I put it... When imagining premise and conclusion as two blocks separated apart, it feels like Strengthening choice not only connects this two by pouring porcelains but the porcelain cover the whole now-connected two blocks. On the other hand, Necessary Assumption choice is like pouring JUST about the right amount of porcelain between premise block and conclusion block so that they would become one block, JUST connecting these two.

Even if I could tell the differences by "sense" in questions, it is just really hard to put it in words when I am trying to reason why those two are different.

Could you tell me your take on this matter?

[chike_eze]

Why do you need to differentiate between the two? They are more similar then they are different. And I think it actually helps to think of them as similar, rather than wasting time trying to figure out why they are different.

Both are asking you for a premise that helps bridge the gap between the other premises and the conclusion. Necessary assumption questions ask "What premise must the author be assuming in making that conclusion?" Strengthen questions ask "What premise will make the author's conclusion more likely?"

Both are asking you for a missing premise. The difference in my mind is that Necessary assumption questions require you to provide a premise that must be true for the conclusion to hold. i.e., if the necessary assumption is false then the conclusion will also be false (and contra). Strengthen questions require you to provide a premise that helps bridge the gap, however, this premise need not be necessary but could be.

Regardless of this difference, they both share the same initial step: you must identify the gap in the argument.

You will notice that some strengthen questions are actually necessary assumption questions in disguise; especially the more difficult Strengthen questions. The reason for this is that any argument will be strengthened by explicitly stating that a necessary assumption of that argument is true.

I think you are a bit too deep in the trees. You need to step back and see the forest.

[tommywallach]

I'm going to disagree here, though Chike's overall thought process is still solid.

In reality, a Necessary Assumption is really no different from a Strengthener.

But a Sufficient Assumption is VERY different. A sufficient assumption means the argument is now 100% true. Strengthens DO NOT DO THIS. Necessary Assumptions DO NOT DO THIS. But sufficients do.

Now, as far as differentiating between necessary assumptions and strengtheners, you could probably drive yourself crazy looking for rules, and still find lots of exceptions, so I'm going to leave that one floating. If anybody else wants to weigh in, they can.

-t