This is a "must be true" question, so you're going to have to PROVE the answer is true using ONLY the premises in the stimulus. If we find the right answer, it MUST BE TRUE, which means it CAN'T BE FALSE. So let's see how that works for answer choice D:

D) In many municipalities there is, or eventually will be, a shortage of rental units.

Let's make answer choice D false and see whether there's anything in the stimulus that gets in the way. Let's do this is study buddy form.

Antonia: I think the answer is D, there will be a shortage of rental units in many cities.

Trevor: A shortage of rental units? Huh uh! There won't be any shortage.

Antonia: It says here rent-control ordinances have negative effects, and one of them is a shortage of rental units.

Trevor: Yeah, UNLESS they are strictly temporary. Maybe they're all strictly temporary!

Antonia: Except it says down here that in many municipalities, tenants get political power. They're not going to give up their low-cost rent!

Trevor: Huh. Well, okay, so, but that doesn't mean there will be shortages.

Antonia: Yes it does -- that's what the first sentence says!

Trevor. Oh. Well, that doesn't mean D has to be right.

Antonia: Yes it does! If it CAN'T be false, it MUST BE TRUE!

Is it Beta? I just heard about it on June 1 (launch day) and am experimenting with it. Didn't have to make any non-disclosure agreements that I recall.

I hate this kind of question. Normally, I read the stimulus very carefully because I find it easier to find the flaw than to match it with the answer. That's especially true here--it is a classic example of an incorrect negation but that's not what the answer says. The credited answer is that the author "overlooks" a negation of the conclusion. That's certainly true, but you could say that about ANY argument.

I guess the take-away is, "If one of the answers is a negation of the conclusion, it might be just what you're looking for!" Somehow I don't see that being all that helpful all that often.

I agree with your hunch, here. Not all strengthen questions involve a necessary assumption, but I think that every "eliminate the weakness" variant does.

Nice insights!

Actually, I don't know why you edited it, but I see I better err on the super safe side. I value the input I get here tremendously, and I am NOT trying to exploit this side to boost my own business. This community is one of the finest places on the Internet for testing out ideas and seeing what is the BEST way to learn the LSAT, and I am eager to promote 7Sage.

Just went over this and got to try out the "A/B" and "/[AB]" explanations. It went great. SO much for making up two new symbols to replace the "double not arrow." Let's go with Quinn's approach!

Admin edit: You know why I edited this. Last warning.

So... I'm still thinking through what you said, Quinn. I hadn't thought of writing down the original statement in the "A or B" form. THAT would be fast, easy, and powerful. Likewise, I should read a "A->/B" rule and write down "/A or /B," which is probably better expressed as "NOT (A AND B)" (which I would write as an AB block with a slash through it.

So... thinking this out... I read "/A->B," and I write down "A/B." I read "A->/B," and I write down "NOT [AB]." Right?

Quinn, I agree with your logic but not your advice. I can figure out "/A->B" on the fly by saying, "So... if A is IN, B can go anywhere, so they can both be in." But... it takes a moment to work that out, and it would take ME a moment to work out the same result using your method. PowerScore uses the "double-not arrow" to save that moment, and I think there is some merit to that. It's just that I haven't figured out a way to reliably USE the double-not arrow for its intended purpose because I'm always second-guessing myself (is that both in or both out? Did I write that down properly?).

Bottom line: there's a trade-off between fast and simple. People who use flashcards are trying to get their speed up by exchanging a thought process for instant recognition. I PREFER working out the logic in my head, but I only have 35 minutes on a logic game section, and a fast, reliable mnemonic may have its advantages.

Having said all that... I love your explanation of the "NOT A or B" mode, and I'm going to try it out with some guinea pigs. If I can explain that effectively, I'll gladly use it instead of a new mnemonic. If I can't, though, I think I'll stick with my "erupting volcano" and "leaky faucet" pictures.

I just posted a new idea that is especially intended to help in/out games. Look for my "better than a double not" post.

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Your argument assumes that "1+1=3" is false without stating that it is false. If you spelled it out fully instead of making that assumption, the atomic proposition would appear twice.

It is certainly possible to make assumptions that are never spelled out in an argument. MOST LSAT questions either don't make such assumptions or else make the assumptions a part of the answer, but that is not always necessarily so as a matter of logic.

In trying to figure out the key parts of a stimulus, I want to be able to assure myself that there's something really there which one really can find if one really looks hard enough. (Really.) If I can count on there ALWAYS being two instances of every "key term" (in the stimulus+answer), then it's worth pushing them to keep hunting until they find it. If it could even theoretically be possible that a well-formed, complete, and non-trivial argument does not have at least two "key terms," both of which appear at least twice, then I don't want to go looking for them.

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Thanks, Quinn. I took academic logic a long time ago... very likely before you were born, which means you're much more likely to be correct than I am, working from memory.

Insofar as the large majority of LR stimuli involve conditional or categorical reasoning, I'm happy to use the term "atomic proposition" if you think it would be clearer than "term." (I certainly don't find the term "term" to be unambiguously clear.)

So, partly echoing you and partly repeating myself from above, there are completely trivial arguments that only use one atomic proposition, but I haven't seen this in any actual LSAT stimuli. Until we discover one, I'm sticking with the observation that a VERY large majority of LR questions have at least two atomic propositions.

Moving on to the more controversial claim--I can't think of a way to write a conditional or categorical argument in which an atomic proposition only appears once. Can you?

I chose the term "term" after looking around hard for another word to express the concept. If you know a better word for the symbols we use in conditional statements, please let me know. I know that logicians routinely refer to the "terms" of a categorical statement as "terms," which is why I used the word in this context.

A->B

A

Therefore B

Good example, @quinnxzhang542. Interesting example, too, since I had gone over it and used it to support the "some people say" principle (which I have discussed elsewhere) without noticing that it broke the "should" principle.

"Normative" is a better term than "moral" for this purpose. It expresses what I wanted to say much better than "moral" does, which has a lot of unnecessary connotations.

In light of the general feedback and specific counterexamples, I'm deleting the "should" principle.

PrepTest 63, Section I, Question 8 has an extreme case of "some people say." I won't quote the actual text, since it is copyrighted, but the logic of it is identical to this:

Student complaint: Professor Smith was wrong to say that "climate science deniers" falsely claim that the earth has not gotten hotter over the last eighteen years. He claimed that surface temperature measurements show a steady increase in temperature over time. But satellite measurements, which are not subject to local "hot spots" and other instrumentation problems, do not show an increase in temperature.

Question stem: what is the main point?

(A) The increase in surface temperature measurements does not support the professor's rejection of the "climate science deniers" claim.

This question pushes the "some people say" principle to its limits... but it also shows the value of the principle. This is a case of "some people say that some (other) people say." Despite the exponential complexity of the case, the right answer happens to be exactly what the "some people say" principle would indicate--the correct answer is, in effect, "What some people say that some (other) people say is wrong."

I'm sorry, @quinnxzhang542, I miscommunicated. What I TRIED to say (as clearly as possible) was that "IF the word should appears in a stimulus, THEN it appears in the conclusion." In a moral argument, "should" often appears as a premise... but I have yet to find a moral argument that uses "should" in a premise but avoids the word in the conclusion.

As @quinnxzhang542't_get_right noted earlier, these empirical observations are NOT logical rules. The fact that the LSAT writers tend to do the same things over and over is NOT proof that they will always do the same in the future.

That said... I'd like somebody to do a little more digging and come up with an actual counterexample. There are a lot of published tests out there...

You guys are truly terrific. Thank you for your honest feedback, and the broader perspective on the LSAT that informs it.

That said... Quinnxzhang, what do you perceive to be the conclusion in PT9.S2.Q20? I think it is "A university should not be entitled to patent the inventions of its faculty members." Do you disagree with that? If so, what do you perceive as the conclusion, and why?

DEEPLY grateful for the all the constructive criticism and counterexamples, folks. I have edited the title of this post (it's a "principle," not a "rule" now).