Book Review: When I read a novel set in a city I know well, I must see that the writer knows the city at least as we...
180October 23, 2013
Negation of the S & F Condition
Greetings I am wondering from the video exposition why wasn't the necessary condition not negated in the contrapositive. For example the author says she can tell if the writer knows the city well as a premise of trusting the writer stories. Why wasn't that negated in the video we are supposed to reverse And negate correct please help me understand this thank you and please enjoy your day.
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The necessary conditions are being negated. The passage states: "When I read a novel set in a city I know well, I must see that the writer knows the city at least as well as I do if I am to that that writer seriously."
We can rewrite that (to be easier to diagram): If the B (book reviewer) is to take the W (writer) seriously, then the WK (writer's knowledge of the city) must be equal to if not more than the BK (book reviewer's knowledge of the city). Hence we diagram:
S ==> WK (greater than or equal to sign) BK
To negate "WK must be equal to if not more than BK," we merely state that BK is greater than WK (the book reviewer has more knowledge of the city than the writer).
If you notice, "the greater than or equal to" sign in the principle rule has been changed to just a "greater than" sign and the BK and WK variables have been switched:
CONTRAPOSITIVE: BK (greater then) WK ==> not S
Likewise with the next two sentences. If a writer is faking, that means that the book reviewers knowledge of the city is greater than the writer's knowledge of the city. So we diagram the second sentence:
BK (greater than) WK ==> not TW
To negate "BK (greater than) WK" we merely state that the writer's knowledge is at least as great as the reviewers.
CONTRAPOSITIVE: TW ==> WK (greater than or equal to) BK
Hope that helps! Let me know if you have any more questions!
180November 14, 2013
Awesome thank you I feel so silly after this explanation.
meAugust 1, 2015
Wait I see two trigger words in the first sentence: "When" and "If". How do I know which one is the sufficient?
NazAugust 4, 2015
Yes. This is a great example of why you should always take every sentence in context. Though there are two triggers for sufficient condition here, ask yourself which is sufficient to know something else.
We are given information on what is required for this person to take a writer seriously. It must be true that a writer knows the city at least as well as the book reviewer does for this book reviewer to take the writer seriously.
The clause introduced by the "when" is merely an overarching umbrella this Sufficient & Necessary statement falls under: in the situation that a writer writes about a city that the book reviewer knows very well, we have the following conditional statement: if the book reviewer is to take the writer seriously, then that writer must know the city at least as well as the book reviewer does.
Always step back and look at the sentence in context, rather than blindly follow trigger word rules.
Hope that clears things up! Please let us know if you have any other questions.
