LRB Chapter 4 Questions

[Stephanie Oswalt]

Below are two questions from a student pertaining to the LSAT LRB. An instructor will respond below. Thanks!

2017 LR Bible Pg 110-111 – Prephrasing with Must Be True and Most Strongly Supported Questions

Problem 1 is clearly a “Fact Set” question; i.e., not an argument. On page 111, the first paragraph indicates the student should “prephrase” a possible answer to the MBT/MSS question. The second sentence states, “To do so, consider the premises together, and look for the connection between the elements...” I do understand there are clear connections between the 3 statements and the question is clearly a “MBT” since it requests the inferences to be drawn from the statements. However, the stimulus is still a “fact set” without a conclusion. In such circumstances, it seems what I am looking for is not so much a conclusion since there is no argument but rather what judgment can be inferred from the 3 connected statements. On the other hand, perhaps I’m just nitpicking?

2017 LR Bible Pg 117 – 119 – Language: Negatives, Double Negatives, and Triple Negatives

Re the Beta cryptoxanthin example on Pg 118, I understand the process of eliminating 2 of the negatives (1st and 2nd “not’s”) to create a single negative statement. My version of that single negative statement was: “Beta cryptoxanthin is listed as a compound that inhibits neurogensis.” Discussion on pg 119 states the single negative as: “Beta cryptoxanthin possible inhibits neurogenesis.” What’s the basis for creating the possibility of negation?

[Jonathan Evans]

Hi,

Good questions!

For your first question, you've noticed a distinction between the common meaning of "conclusion" and its meaning in logical reasoning. Typically, the term "conclusion" indicates a determination that "makes sense" or would be a "likely outcome" of a set of circumstances.

• e.g. I'm hungry. I haven't eaten all day. There's a delicious piece of cake in the fridge with my name on it.

You might conclude I'm going to eat that slice of cake! However, this conclusion does not necessarily follow from the given premises (I could eat a banana instead).

For the LSAT, when we refer to a "conclusion" we mean a "proposition that is reached from given premises." In this sense, "conclusion" is synonymous with "inference," literally "a conclusion reached on the basis of evidence and reasoning."

There is still nuance between these two terms. We would more frequently refer to the "main conclusion" than to, say, the "principle inference" of an argument. However, for most purposes, you can use "inference" and "conclusion" largely interchangeably.

For your second question, you have to be very careful with statements that include negation. In this case, parsing the double negative goes beyond simply excising both "not"s from the sentence.

The book discusses the importance of this nuance in the explanatory paragraph:

Remember, the topic under consideration does not have an effect on the logical structure of the sentence, so try to look past the topic to see what the sentence is actually saying.

Start by explaining to yourself what the statement means:

• The BC is not on that list of compounds. Which compounds? The compounds that don't inhibit neurogenesis.

What do we know about the BC? It's omitted from the list of compounds that don't inhibit neurogenesis.

So... what can we say for sure about BC? Since it's not on the non-inhibiting neurogenesis list, it could maybe be a compound that does inhibit neurogenesis. Do we know for sure that it does inhibit neurogenesis? No, we don't know that for sure. Not every compound that's not on that list necessarily inhibits neurogenesis. For instance, maybe sodium chloride isn't on that list. Do we know whether salt inhibits neurogenesis? Not necessarily. Maybe it does. Maybe it doesn't. It just isn't on that list.

Thus, understanding this statement (and other difficult statements) often hinges on your description or accurate paraphrase of what a statement means.

I hope this helps!

[marieallen]

So I'd like to take this one step further with you. The reason the Bible text introduced the "possibility of BC on the inhibitor" list is that "could be true" is a logical opposite of the statement, once the triple negatives are reduced to a single one. Thus, in reading the answer choices, it is appropriate to keep any answer as a "contender" that by wording, allows for such a possibility. In other words, a "loser" would include any answer with too strong a wording (e.g., "will," "must," "always," etc.).

Hope I'm not nitpicking this!

[Adam Tyson]

That doesn't sound too nitpicky, Maria, and you're right on the money there! If a statement says something is impossible, you can negate it by saying it IS possible. Well done!