2017 LRB pg. 78

[Stephanie Oswalt]

We recently received the following question from a student. An instructor will reply below. Thanks!

I'm currently using the 2017 edition of the Logic Reasoning Bible and I think I have found a typo but I'm not sure. It is possible that I am viewing the content inaccurately.

Its the first sentence of page 78. It states "If any answer choice contains information that does not appear directly in the stimulus or as the result of a combination of items in the stimulus, then the answer choice could be true and it is incorrect." This is referencing the Fourth Question Family. It is the second rule pertaining to this family. I feel that the word "not" shouldn't be used. This is quite important because the use or lack of the word in this situation would change the meaning of the statement 180 degrees.

Thanks for your help with this matter.

Cameron

[Dave Killoran]

Hi Cameron,

Thanks for the question! Fortunately, there is no error in the text. This is a difficult idea, however, so let's talk about it a bit more.

The first important thing to notice is that these are Cannot Be True questions. That fact turns everything upside down from what you'd expect, because instead of proving a point, you are actually trying to find something that cannot possibly occur. That sounds easy, but in practice these questions are often troublesome.

The second key is to understand that anything that is possible is immediately a wrong answer; only impossible things could be correct. So, if something can occur, then it will be wrong. Well, what types of things would fall into the "could occur" category in a question like this? One big area would be topics or information that did NOT appear anywhere in the stimulus. Why? Because if something wasn't addressed in the stimulus, then it can't be directly ruled out, and thus could never classify as Cannot Be True.

So, in this case, the "not" is extremely important, because if something is not talked about in the stimulus, then for sure it would be possible, and thus an incorrect answer. I know that sounds convoluted, but that's the effect of the Cannot question type—it can get your head turned around!

Please let me know if that helps. Thanks!