Necessary Assumption Questions

PreWorkout

YOOOO! I just wanted to ask a quick question about the must be true test for Necessary Assumption answer choices? could someone elaborate on that? Im confused with it. Specifically for the Rattlesnake question JY gives us in the lesson. The AC has to do with food which was never even mentioned in the premises/conclusion. How do we determine whether foreign information is relevant to the argument?

BinghamtonDave

The necessary assumption is something that must be true in order for the conclusion to follow from the state premise(s). Sometimes, this assumption is going to take the form of a "blocking" assumption. I like to think of these particular assumptions as something that must be true in the background of our argument, an assumption that must be operating in a specific way in order for our argument to function. so the rattlesnake question has this basic core:
-Because a new section of the tail forms each time the snake molts
-We can reliably determine the age of the snake by counting the number of sections (paraphrase)

What must be true in order for this conclusion to follow from this stated premise? what must be true is that the concept of "molt" must have some reliability in it, meaning we must be able to deduce something about a time frame from the action of the molt. What if the molting occurred in some randomly generated impossible to predict sequence individually tailored to each snake's habitat, diet, stress levels etc? Like, between molting 1 and 2 was 4 years for one snake, between molting 2 and 3 was 9 days for that snake and between molting 3 and 4 was 6 hours for that snake and on top of that each individual snake was drastically different? Then how could we reliably tell the age of two different snakes with 4 sections of rattles? One could be 9 days old and the other could be 3 months 2 weeks and 5 days old.

Answer choice (E) attempts to control or make level at least one aspect of the playing field when it comes to the snakes molting. Now, notice what we might predict going into the answer choices and notice how far (E) is from that. What we might predict is something like: the molting happens with some/in some reliable time frame (regularity). (E) says that food scarcity or availability does not have an effect on the time frame that the molting happens, meaning that molting does not depend on this external factor that would make the job of calculating the snakes age from the number of rattles which relies on molts very, very difficult. This is necessary. This is relevant to the argument because at bottom it deals with the molting.

Now, notice what is not necessary here: (A). We don't need it to be the case that the snakes molt in that specific time frame. They can molt once every 6 months. As long as we can deduce the age from the molting that occurs with some regularity, we don't need that molting to occur in a such specific timeframe, we just need it to occur in some time frame that we can rely on
(the basis of our calculation of age). It's not necessary that it need occur in this specific time frame.

I hope this helps
David

Cant Get Right

David explains all this really well, and I just want to jump in to reinforce because this method is one I really embrace and hope to see it replace Negation Technique as the new standard, at least for all those already testing in the 160's. I almost don't even want to call the question type Necessary Assumption. It's such an entrenched terminology that it wouldn't do to change it, but I'd rebrand it to Conditional Must Be True if I could have my way. The concept is logically identical, but I think the name suggests the better approach. The sufficient is the validity of the argument: If the argument is to ultimately be made valid, Then what Must Be True? I think this gets more directly at the concept of what it really means for something to be logically necessary.

No study of NA is complete without revisiting JY's lesson on what necessity even is: The one about basketball, so check it out if you haven't recently. This lesson was a major breakthrough for me; I must have watched it a dozen times when I first came across it. This was the first time I really understood the concept of necessity, but I was still trying to answer these as some weird cousin to SA questions. What I've come to learn though is that NA (CMBT?) and SA are about as different as any two question types can be. MBT is the much better type to pattern CMBT questions off of. Once I both understood the concept of necessity and how to think about answering them more intuitively, these turned from a liability--both on my accuracy and on my time--to an enormous strength. Not only would I get these correct, I'd be finishing even the 5 star questions in the time that before I would still be struggling to negate the first AC. The CMBT approach works the same logical principles as the Negation Technique, it's just much more direct and intuitive.

maryyiam

@"Cant Get Right" What is CMBT?

Cant Get Right

@maryiamimam said:
@"Cant Get Right" What is CMBT?

Conditional Must Be True