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Mehran on March 16, 2018

These concepts are discussed throughout the Sufficient & Necessary lesson and are directly related to the transitive property and what you can properly conclude from S & N statements.

Let's try a missing premise drill together to see if it helps:

P: B ==> Not X

P: ?

P: Not A ==> Z

C: Not Z ==> Not X

Okay so first these are Strengthen with Sufficient Premise questions in the abstract.

The idea is there is a gap in the argument and we are looking for the answer choice that would make the conclusion follow logically.

Notice the sufficient condition of your conclusion is "not Z" so that is where I will start.

Contrapositive of P3 is Not Z ==> A

So we have A but then we are stuck because A is not a sufficient condition of any of our premises.

So the jump here clearly will relate to A.

We are trying to get to "Not X" because that is your necessary condition of the conclusion.

P1 gives us "Not X" because "B ==> Not X"

So if we can connect A to B we would complete this argument logically as follows:

not Z ==> A ==> B ==> not X

So the missing premise is A ==> B.

Hope that helps! Please let us know if you have any other questions.

eades_309 on March 24, 2018

Hi! I'm also struggling with the Missing Premise drills. I've rewatched the lecture but can't seem to grasp it. Can you give another example? Thanks!

Mehran on April 4, 2018

Did the example above make sense?

jennealvarado on April 10, 2018

I'm having trouble with the same concept. However, I can't follow with your example above as some of the characters are experiencing text encoding issues. For example, I am seeing the following:

"We are trying to get to 'Not X' because that is your necessary condition of the conclusion". Could this possibly be fixed or could another example be given?

Thanks!

Mehran on April 11, 2018

Not sure I understand.

You are only seeing "We are trying to get to 'Not X' because that is your necessary condition of the conclusion"?

jennealvarado on April 13, 2018

Hi Mehran,

I believe I finally understand how to do the drills, but I have one more outstanding question. I'm getting the correct answer for the missing premises, but there are times that I get it backward. What I mean by that is that I usually have my answer as the contrapositive or vice-versa. So my question is, does order matter? Does it matter whether I'm using the contrapositive as my answer? I hope this made sense.

Thanks in advance for your help!

jennealvarado on April 13, 2018

Nevermind! Figured it out. Thanks!

Mehran on April 15, 2018

Great but just in case any one else reading this thread is wondering, the contrapositive is identical in meaning so it is absolutely the correct answer.

Remember, you will never see both as answer options on an LSAT question because that would mean there would be two right answers.

Hope that helps! Please let us know if you have any other questions.

djayasinghe on May 10, 2018

Hi Mehran, your explanation did not work because it did not appear in common letters, it showed up in an unusual way, as Cydney said. Can you reupload your explanation? If you don't see what I mean, try logging into a different computer and seeing it, because on our end, the formula explanations your produce arent coherent

pepperlei on August 5, 2018

Hi Mehran, I keep getting close to the right answer on missing premise, but sometimes I mix up which side the "not" should be in the answer. What's the trick to breaking that down? Thank you!!

Anna20 on May 16, 2020

Hi @Mehran, Team - Grateful if I could please follow up on this thread. Are all these questions Strengthen with Sufficient Premise questions?

Could someone please walk through the following Missing Premise drills:

P: A --> Y
P: ?
P: B --> C
____________
C: not Y --> not B

When I did this question, I got the contrapositive - C --> A (following the transitive property of B --> C --> A --> Y). I understand that the contrapositive generally has the same meaning as not A --> not C - however, to what extent can you manipulate the contrapositives for these exercises? I also had the same issue with P1: D --> A P2: C --> D P3: ? C: not X --> A. For P3, I got not X --> C.

Separately, please could you also explain:

P: X --> Z
P: not Z
P: ?
______
C: A

I was completely stuck on the following (how do you combine this to take advantage of the transitive property? - Why is this question especially causing difficulty? Is there a pattern here to beware of?)

P: not X --> not Y
P: ?
-----------------
C: not X --> not B

Thanks so much in advance for your help! Very much appreciated.

Anna20 on May 29, 2020

Please can I follow up on this. Thank you.

Anna20 on June 2, 2020

Please can I follow up on this. Thank you.