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Ariel August 12, 2020

Not understanding Sufficient and Necessary Section

Hello, I was not able to do the premise nor argument drills because I don't understand how to do them. I am also struggling to complete the sufficient necessary questions on my own without the explanations but I don't find the explanations helpful either. I am feeling hopeless at this point. What can I do to finally understand how to do these questions on my own?

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Ravi August 13, 2020

Hey there, for the missing premise and argument completion drills, you're looking to plug something in so that you have a complete chain from the premises all the way to the conclusion. If you have specific ones you'd like help with, please let us know, and we'll be happy to walk through them.

For the sufficient and necessary questions, it sounds like you may need to rewatch the lectures to better familiarize yourself with the different elements of conditional logic. Sometimes you might need to to rewatch a lecture once or a few times to let everything sink in, as there's a lot that's covered in each module.

Let us know if you have any other questions!

Ariel August 13, 2020

Thank you for answering. Yes one example for the premise drills is..... P: A -> B P: ? C: not B -> C.

I looked at the explanation but I don't understand how they figured out what goes in the premise.

Ariel August 17, 2020

Hello,

Can someone please answer this for me. Im trying to figure out how to complete these premises

Victoria August 18, 2020

Hi there,

I would suggest looking at the Message Board for the Missing Premise Drills as a variety of walkthroughs have been posted in the past, but I'll walk through the example you've posted above to see if this helps clear things up a bit!

The Missing Premise Drills are designed to familiarize you with the pattern of logic discussed in the Sufficient & Necessary Premises lesson. LSAT exam questions can be thought of as word problems. These drills are just simplified versions. We have removed the words, which students often find confusing, and have brought it back to the basics - just the variables.

Your goal in these drills is to connect everything you are given to figure out what is missing.

The first step is to identify all contrapositives. The second step is to look to connect the variables to come up with the missing premise.

So, let's start by finding the contrapositives here.

P: A --> B
Contrapositive: Not B --> Not A

P: ??
Contrapositive: ??

C: Not B --> C
Contrapositive: Not C --> B

Essentially, what we want to do is make a transitive chain, but we are missing the middle piece.

Not B --> _ --> C

Notice that the contrapositive above says Not B --> Not A. Therefore, our missing premise must connect Not A and C.

P: Not A --> C
Contrapositive: Not C --> A

The way to double check if you are correct is to make the transitive chain and see if the conclusion can be properly drawn.

Not B --> Not A --> Not C = Not B --> C

Contrapositive: Not C --> A --> B = Not C --> B

Hope this helps clear things up a bit! Please let us know if you have any further questions.