Which one of the following statements most accurately characterizes a difference between the two passages?

Johnathan on May 9, 2018

Valid/Invalid Arguments #2

Hello - what confuses me about this portion is that we're told the premise of "anyone named Sue is a girl" is false, which I understand, but then we're also told to "assume all premises we're given are true". So, where is the line on when to assume all premises given are true and when to question them? Thanks!

7 Replies

Johnathan on May 17, 2018

Hello - I wrote this message over a week ago.

Johnathan on May 17, 2018

I am completely lost on the "Missing Premise" drills. I can mostly follow the video lectures and the questions themselves, but I have absolutely no clue how to answer these missing premise questions. I'm not going to look at them anymore since they're only confusing me.

Abby on May 17, 2018

I'm pretty sure, and this may be incorrect, that the argument is actually valid. Watching this video is bringing back the information I learned in logic class and, I believe, that as long as a conclusion is true based on premises it is valid even if the premise(s) is a false statement. The argument is certainly flawed but still valid. However, I took logic 7/8 years ago so I may just be remembering incorrectly. There will be, and are, many times that you are not sure of the truth of a premise without research.

on May 21, 2018

Johnathan,

You are not alone. I am severely lost. I have watched the video twice now and about to do it again. I am struggling with the questions and really have no clue where to go for guidance except to find a live class.

Mehran on May 22, 2018

Hi @jnucci & @Priska thanks for your posts. As stated in the video lesson, in the history of the modern LSAT, there have perhaps been two questions that have weakened an argument by pointing out that a premise is false. This is why we advise students to assume that all given premises are true. On those exceedingly rare occasions when you weaken an argument by stating that the premise itself is false, it should be fairly straightforward (e.g., not everyone named Sue is a girl . . .).

Hope this helps. Please let us know if you have any additional questions.

on May 28, 2018

I think this is best posted here and not in a separate thread, but to add on to a point from anonymous (4th message), I believe that the argument about Sue is actually valid, in a technical way of speaking. However, it is not sound (meaning not all premises are true), to use another technical philosophy term. That is to say, it really is valid, and also "flawed," because it is not sound. At least, this is what my philosophy program teaches. Perhaps this is not of import to LSAT prep, or maybe it is just some sort of convention to define validity and soundness in this way, but I am just concerned that the lesson in this video can be easily applied incorrectly, though I don't think the LSAT asks to identify valid and sound arguments, or distinguish between these. Anyways, I just wanted to voice my convert over words being misused, and would appreciate any reasoning behind this choice.

Christopher on June 6, 2018

The Boy Names Sue reference is meant as a joke and doesn't reflect the way that LSAT questions work. The only information that matters on any question is the information that is written on the page. You won't need to know Johnny Cash's discography or anything else going in.

So the the argument about Sue is valid, given the information that you have on the page. It is possible that they create a question that provide evidence directly contradicting a key premise, but that information will be explicit and not based on the assumed knowledge of the reader. More often, they test makers will provide information that calls the USE of a premise into question but not the truth or untruth of the premise. The point of the exam is to test your ability to evaluate the logic - not to prove your exhaustive knowledge about masculine names.

Does that clear it up?

To some extent, this issue become moot as you progress in the class because you will not run into questions that require outside knowledge to answer.