The author uses the word "immediacy" (line 39) most likely in order to express
Partvon April 30, 2020
Missing Premise Drills
For the flashcard missing premise drill problem: P:? ; P: not B --> A ; C: X --> B
I answered that the first premise would yield not A --> X but the answer key states that not X --> A. Is my answer still correct? if not, how come? I keep swapping the two right variables.
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Hey, I made the same mistake then I realized that for drill 23 of 30 the answer on the flashcard is actually "X - not A" or the contrapositive "A -> not X". It seems like you have the right variables and applied the negation, but forgot to reverse them.
That's my guess...
Skylaron June 25, 2020
@Partv, happy to help!
@AnthonyH is correct- the answer to this drill is "A -> not X" and "X -> not A." Great job!
Let's take a look at the drill. We are given: P: ? P: not B -> A C: X -> B
Our first step should be to find the contrapositives of all our given statements. This gives us: P: ? P: not B -> A not A -> B C: X -> B not B -> not X
Now, we need to connect the information. We know that there is a new variable in our conclusion- X. We'll want to include this in our missing premise somehow. We also know that we want to be able to conclude "B." Do we have any other statements that allow us to conclude "B"? Yes, the contrapositive of our given premise says "not A -> B." Since we want to be able to say "X -> B," we should therefore say "X -> not A." This allows us to make a larger chain of "X -> not A -> B." This simplifies into our conclusion, "X -> B." Therefore, our missing premise is "X -> not A." Its contrapositive is "A -> not X." Since contrapositives are equal in meaning, it does not matter which we write first as the original missing premise/which we write as the contrapositive of the missing premise.
So, our final diagram looks like: P: A -> not X X -> not A P: not B -> A not A -> B C: X -> B not B -> not X
Does that make sense? Hope it helps! Please let us know if you have any other questions!
Partvon July 2, 2020
This helps! It tethers to what was said in the video lecture: The sufficient can never be concluded, so me switching the A and X concludes X and not B!
