The author uses the word "immediacy" (line 39) most likely in order to express
haleson June 25, 2019
Sufficient and Necessary - Example 8
On question eight I have a clarifying question. The rule used to correctly identify the flawed logic in the explanation was "don't just negate" - however, when I solved on my own, I used the contrapositive and saw it as invoking N to conclude S. Would this also be correct? What is the difference in these two? When doing this I also came to the correct answer. Will this always be the case, or was this just a fluke instance?
Do you have any recommendations for which rules to use on these types of questions - is it ok to use the contrapositive?
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Great question. The truth is that it doesn't really matter how you diagram it as long as you understand what the symbols you're using are referring to so you don't get confused.
I recommend using the shortest possible symbols/words/phrases for you to capture what's going on. This way, you're being efficient, but you're also covering everything.
Instead of writing "distinguish," you could even just write "D" to connote the phrase you're identifying as the necessary premise.
Does that make sense? Let us know if you have any other questions!
Ravion June 25, 2019
@hales, please ignore the above response (that was for one of your other questions). I'll post another reply on this thread for this one.
Ravion June 25, 2019
@hales,
Great question. When Mehran was saying, "Don't just negate," he was referring to the error in the reasoning in the stimulus. The stimulus said
PL - >O
and the argument concluded
/PL - >/O (this is what don't just negate referred to)
The contrapositive of the argument's conclusion is O - >PL, and this is exactly what you picked up on (invoking N to conclude S). This is the same mistake that Mehran is referring to, so you're on the right track with your analysis.
It's always o.k. to use the contrapositive since it's a logically equivalent statement, so you're good there. Regarding which rules to use, there's not hard rule—it really depends on the question. You're doing great with how you're currently looking at it.
Hope this helps. Let us know if you have any other questions!
