# The author uses the word "immediacy" (line 39) most likely in order to express

Savannah on January 8, 2019

Question about missing premises

How do you find the missing premises? I understand how to answer these questions, and understand the sufficient and Necessary rules. But for example if something gives you: (this probably makes no sense but these are the questions I don't know how to answer) A>not B Missing Conclusion- C> not A How do you go about answering these? What are the steps to finding the correct answer? Do you need to do the contrapositive and the answer will pop out? I just have no idea how to approach problems such as these

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Ravi on January 8, 2019

@SavannahM,

Great question! It's great that you're feeling comfortable with S + N
rulesâ€”that's a good sign that you'll soon be able to conquer these
questions as well.

In going about answering these questions, it often helps to do the
contrapositives of the given statements so that you can easily see how
everything can link up. While you don't always have to do the
contrapositive for each given statement, it often helps. In the
example you give, it helps A LOT.

A - >not B

Missing

C: C - ->not A

Taking the contrapositive of the first premise, we have B - -> not A

How can B - ->not A plus another premise make the conclusion that C - ->not A?

What if C - ->B? We need to bring in the variable C so that it's in the
premise as well, and we need it to connect to the other premise so we
can have a conclusion that makes sense.

If C - >B, and B - ->not A, we have the chain

C - ->B - ->not A

From this, we can conclude that C - ->not A

Does this help? Do you see how taking the contrapositive of the
premise helped us see more clearly how to link up the statements
together to find what was missing?

Let us know if you have any additional questions!

Savannah on January 8, 2019

It helps a little bit, would you do the same thing in order to find the conclusion as well?

Ravi on January 13, 2019

@Savannah, where else are you getting stuck? Let us know, and we'll be
happy to explain it in a different way so that it clicks.

Yes, using this strategy to find the conclusion works well also. The
key is to have all of the information arranged in a manner where you
can easily see how the different conditional statements can link up to
each other to form a train that connects everything up.

Let us know if you have any other questions!