Before Session 3 Homework Quiz Question 4

[laural421]

The question is as follows: "Turn to page 18 of PrepTest Book 1. If question 16 were a necessary assumption question, which 2 answers would be correct?"

I opened the green PrepTest book---PT 52-61. I have no idea what they are asking.

Feedback: I haven't found the homework to be sufficient to explain the Necessary/Sufficient assumption questions. I spent a lot of time outside of Manhatten Prep to get a grasp on this section.

[ohthatpatrick]

Yeah, I often warn my students as we're starting to discuss Nec and Suff Assump, "This is possibly the concept students struggle with the most. Don't feel like you need to master it this week. Students are usually STILL asking about this even as the course ends."

It's pretty simple to define them, but it takes a lot of practice to feel comfortable applying them.

SUFF ASSUMPTION = if this idea is true, then I can add it to the existing evidence and mathematically derive the conclusion.

NEC ASSUMPTION = if this idea were false, it would badly weaken the argument


full disclosure -- I don't love this HW Quiz question (it's just an annoying amount of hassle to get to that problem, w/o much payoff).

I lost my copy of OG1, so I'm assuming I'm looking at the correct question here:

If you're looking at PT 56, sec 3, Q16,
and the HW question was "Which of these would be Necessary Assumptions?"
then you would just ask yourself, for each answer choice,
"If this were false [i.e. If I negate this], would it badly weaken the argument?"

The argument:
CONC: If you don't have trust, you can't be happy
EVID: If you don't have trust, you will feel isolated and w/o meaningful emot connections

hopefully we can hear the missing links are "If you feel isolated or you don't have meaningful emotional connections, you can't be happy"

negating (A)
"Some people who are feeling isolated can feel happy".

Would that weaken? YES. That is the opposite of what the author was assuming. The author thought that you can't be happy without trust, because having no trust means you feel isolated (and she's assuming that if you feel isolated you can't be happy). Negating this answer goes against that: "some people who feel isolated CAN feel happy". Since the negation weakened the argument, (A) would be a necessary assumption.

negating (B)
"at least some people who have meaningful emotional connections are not happy".

Would that weaken? NO. The author believes that people WITHOUT meaningful emotional connections are NOT happy. It doesn't interfere with that thought to hear that some people WITH emotional connections are not happy. Since the negation didn't weaken, this isn't a necessary assumption.

negating (C)
"you can avoid feeling isolated even if you don't trust other people"
i.e. it's possible to not trust other people and not feel isolated.

Would that weaken? It would actually contradict. The author's evidence says
"Not trust --> no meaningful connections -> feel isolated"
So is this a necessary assumption? Sigh, it's very complicated.
This is why I think this HW question is dumb.

So ... (C) reiterates a conditional connection we already knew from the prompt.
~Trust --> ~Meaningful Connection -> Isolated

From that chain, we know that
~Trust -> Isolated
~Isolated -> Trust

(C) is saying "~Isolated -> Trust"

It's hard to call (C) a necessary assumption because it's just reiterating something we already knew. Assumptions are "unstated" ideas, but the idea in (C) is already fully knowable from the evidence. However, the author never explicitly said this.

If an author says A leads to B and B leads to C, is she ASSUMING that A leads to C? Honestly, I'm not sure and have never had to question whether that is so because LSAT has never written an answer choice on Necessary Assumption that behaves this way. Assumptions should be ideas that may or may not be the case. The idea in (C) is already fully inferable from the evidence so it's not a toss-up whether (C) is true. We already know it to be true from the evidence.

If you merely applied the negation test to (C) and asked, "does this weaken the argument?", you might say "Yes, it contradicts a premise". But LSAT doesn't ever provide answer choices on Necessary Assumption that reiterate a premise or provide a derivable inference from the premises.

Here's a quick example
"Jerry is a boy. All boys like cool vehicles. Thus Jerry must like monster trucks."

Which needs to be assumed?
(A) Jerry likes cool vehicles
(B) Monster trucks are cool vehicles

The correct answer would be (B). (A) would never show up as an answer choice on Necessary Assumption. From the two premises, we already know Jerry likes cool vehicles. It's not being assumed. It's just something rational beings can know by synthesizing the 1st and 2nd sentences. Remember that assumptions have to do with getting from the evidence to the conclusion, so even though negating (A) would weaken (i.e. contradict) our premises, it wouldn't hurt "the move" the argument is trying to make from
"Jerry likes cool vehicles" to "Jerry likes monster trucks"


negating (D)
"zero people who feel not-isolated are happy"

Would that weaken? No. The author is making an argument that concludes that certain people would be UNhappy. He doesn't need to assume anything about people who would be happy. I don't know why our quiz answers would say that (D) is necessary (maybe I'm looking at the wrong problem)



negating (E)
"there's at least one person who DOES trust, but who does NOT have any meaningful emotional connections."

Would that weaken? No. The author is only discussing what happens when you don't trust people. She doesn't need to assume anything about people who DO trust.


Okay, that was probably a huge waste of all of our time.
I'm guessing it got confusing enough that you don't sense much payoff, and I'm either looking at the wrong problem or disagreeing with the answer key to our quiz.

Let's circle back to the initial takeaways of:
- this HW question is not worth our effort and probably shouldn't exist

- SUFF ASSUMP = an idea that, if true, could be added to the evidence and allow us to derive the conclusion

- NEC ASSUMP = a previously unstated / unknown idea that, if negated, would badly weaken the argument