LR Bible 2020 Edition, Chapter 21

[sim.LSAT]

Hi,

I have a question regarding Chapter 21 in the LR Bible. It states on page 21 the items that can be concluded, which includes 2 scenarios. However, in the explanation to Question 1 on page 668, it states "Remember, there is no way for you you to conclude that a sufficient condition has occurred or that a necessary has not occurred." Is this not in direct contradiction to both the statements made on page 21? I'm not sure what I am missing here....

Thanks in advance

[Jeremy Press]

Hi sim,

When the LRB is talking about "What You Can Conclude," it's referring to what the conclusion of the answer choice can safely say. So for the first examples, it's saying that if you knew the sufficient condition was met (in other words, if the premises of the answer choice told you the sufficient condition was present), then you'd be able to conclude the necessary condition has also occurred (so the answer choice could make a valid conclusion that the necessary condition had occurred).

For the second example, it's saying that if you knew the necessary condition was not met (in other words, if the premises of the answer choice say that the necessary condition did not occur), then you'd be able to conclude the sufficient condition also did not occur (so the answer choice could make a valid conclusion that the sufficient condition did not occur).

So what those two examples tell us is that the only two conclusions in answer choices that are valid in this context are that (1) a necessary condition occurred; or (2) a sufficient condition did not occur.

Since the conclusion in answer choice B is that a necessary condition did NOT occur, it doesn't fit those two criteria, and we won't be able to make a confident conclusion about it. Similarly, the answer choice wouldn't be able to make a confident conclusion that a sufficient condition DID occur. That's what the explanation means when it says "there is no way for you to conclude that a sufficient condition has occurred, or that a necessary condition has not occurred." It just means there's no way for the conclusion of the argument to validly say either of those things.

Let us know if that clears it up!

Jeremy

[sim.LSAT]

Hi Jeremy,

Thank you for the reply.

So, "What You Can Conclude" is based on the idea that the answers represent a valid argument argument form. That is, either the repeat or the contrapositive. If this is the case, then why in Question 1 do we look for an answer that is completely the opposite. Wouldn't we want to a valid argument form in the answers? Or an answer that shows that either the necessary did not occur, or the sufficient did occur? If we did look for a valid argument form in the answer, then wouldn't the answer's judgement match the valid judgement made in the stimulus?

I guess, I am confused as to why "only two conclusions in answer choices that are valid in this context are that (1) a necessary condition occurred; or (2) a sufficient condition did not occur."

[Jeremy Press]

Hi sim,

No problem, and thanks for following up!

The reason those are the only two valid conclusions in this context has to do with the nature of conditional reasoning. In conditional statements (for example, the two principles that are stated in the stimulus of this question), we only have information about two things: a sufficient condition and a necessary condition. So we have only those two things to rely on to derive any conclusions.

In conditional statements, the occurrence (or the presence) of a necessary condition does not tell us anything about the occurrence (or the presence) of a sufficient condition. This is because a necessary condition is an event whose occurrence is independent of the occurrence of a sufficient condition. That's just the nature of being a necessary condition. So we'll never be able to make a confident conclusion that a sufficient condition occurred from the occurrence of a necessary condition. That's why the arguments in the answer choices here could never validly conclude that a sufficient condition occurred. On the other hand, since a sufficient condition is dependent on its necessary condition, if we know that the sufficient condition occurs, we can be absolutely certain that the necessary condition occurs as well. That's why the arguments can validly conclude that a necessary condition occurs (so long as the premises tell us the sufficient condition occurs).

By the same token, since the necessary condition can occur without the sufficient condition occurring, we'll never be able to make a confident conclusion that a necessary condition did not occur just from knowing that a sufficient condition did not occur. That's why the arguments in the answer choices here could never validly conclude that a necessary condition did not occur. On the other hand, since a sufficient condition is dependent on its necessary condition, if we know from the premises that the necessary condition does not occur, we can validly conclude that the sufficient condition does not occur (if it did occur, the necessary would also have to occur).

Let me know again if that helps!

Jeremy

[sim.LSAT]

Okay! I think this makes sense now.

However, I do have one question in regards to answer option D:

In answer choice D, the author concludes that Walter did lie (or in other words, that the necessary condition occurred, which is valid). He also, then shows us that the sufficient occurred (intended to deceive, which matches the reasoning used in the stimulus.) So this answer is clearly correct.

However, what if the author of answer choice D concluded that Walter did lie (which is valid), but then says "he did not attempt to deceive" (so the sufficient did NOT occur). Would his conclusion be invalid or valid? Would this be a mistaken negation?

[Adam Tyson]

Let's write that out and see what we have! "Walter's claim to a potential employer that he had done volunteer work was a lie. Walter had worked without pay in his father's factory, and he did not use the phrase "volunteer work" in an attempt to deceive the interviewer."

In that situation, sim.LSAT, the conclusion that Walter lied would not be valid because there would be no reason to believe that he had lied. In the absence of the sufficient condition (intent to deceive or failing to clarify a misinterpretation), we cannot know whether or not the necessary condition occurs, so concluding that it did occur is unsupported. Also, the answer would no longer "conform to the principle" because it wouldn't be following the rule in the principle. It no longer has anything to do with the principle, really.

Necessary conditions aren't things that are always true. They are things that must occur IF the sufficient condition occurs, and which MAY occur even when the sufficient does not. The only time you can prove that a necessary condition occurs is when the sufficient condition occurs.

The question of whether a claim is "valid" is not a question of whether that claim is objectively true. It's about whether that claim is logically supported by one or more premises. If I say "I'm happy", we cannot say whether my claim is valid or not, because it was not connected to any supporting statements. But if I say "I am always happy when I am working, and I am working right now, so I am happy," then we can say my claim is either valid (logically supported by the premises) or invalid (NOT supported by the premises). It doesn't matter whether it is true that I am always happy when I am working (I usually am, but not always), because we aren't evaluating truth on the LSAT. What matters is whether those premises provide sufficient support to reach that conclusion (they do - it's a valid argument). So we cannot say that the conclusion "Walter did lie" is a valid claim unless we evaluate it in light of whatever premises were used to support it.

I hope that helps clear things up!

[sim.LSAT]

Thank you! The last paragraph really helped.