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Olivia on January 19, 2020

Missing Premise Drills

I did pretty good with the questions in the video, but I am having difficulty with the missing premise drills. What would be the best way to get clarity on these, is there a part of the video or is it just deduction and I really don't understand the rules if I'm not getting these?

1 Reply

on January 20, 2020

Hello @oliveds,

These drills are somewhat abstract, so they are different from what you will see on a test. However, they are very helpful for practicing with sufficient and necessary reasoning. I'll walk through one of these drills, maybe that will help.

P1: X - -> not D
P:2 ?
P3: B - -> D
C: B - -> A

First things first, we notice that our conclusion says something about A. But, with our given premises, we know nothing about A. We will need to provide it in the form of our missing premise. Keep that in mind.

We do know something about B. Where does B factor in? Look at premise 3. We now have D. What does that lead to? According to premise 1, we now have not X.

At this point, we have used both of our given premises.We last concluded not X. We can now bring in A.

P2: not X - - - > A

This leads us to the conclusion, using each of our premises.

The conclusion gives us the starting point and the ending point. We were given B, and we followed the chain of reasoning. Then, we plug in our missing premise that includes the information we need to reach the end.