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Diamondon January 20, 2022
Missing Premise Approach Clarification
I understand the lecture on S&N but he doesn't talk about how to go about missing premise? I can see on some questions that you want to make a chain in order to use the transitive property...but on others it seems random. Sometimes I answer the missing premise with what the answer has as the contrapositive but it's hard to definitively know when to use what.
For Example:
P: not X -- not y
P: ?
C: not X -- not B
I started with the CP of P1 and C
P: not X -- not Y
Y -- X
P:
C: not B -- C
not C -- B
Then I didn't see how those helped so I just brought the "not Y" from P1 down to P2 and added the new N condition that is in the conclusion to make use of the transitive property.
P: not X -- not Y
Y -- X
P: not y -- not B
B -- Y
C: not B -- C
not C -- B
But the answer for the missing premise is B--Y so am I still wrong? How do you know when to work from the contrapositive or not? in other examples, this approach works so what's the step by step process for missing premise drills? Is there a video somewhere?
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Nevermind! I found the office hour video that extrapolates on missing premise drills!
Naryan-Shukleon January 22, 2022
Hey @Diamond,
Great questions! And yes, there are ample office hours that dive into these topics, so make sure to check them out.
As for missing premise questions, think of contra positives as a tool, not a rule. If the variables aren't lining up, or if there are variables that line up but in inverted form (A and notA), then trying out a contra positive can very often get you to the answer.
A word of caution - lots of people take the contra positive of everything. This isn't necessary! Sometimes you only need the contrapositive of one statement, sometimes none. Save yourself the work, and flip statements only when it helps you reach the answer.
