Linking Assumptions (PT51, S1, Q16)

*Ari*
Posts: 47
Joined: Sun Dec 05, 2010 1:20 am

Linking Assumptions (PT51, S1, Q16)

Postby *Ari* » Mon May 02, 2011 12:18 am

Hi,

I am just wondering if someone can explain to me the reasoning behind knowing how to establish the contrapositive to link the assumption to the conclusion.

Anyway, the conclusion of the question is individuals are not always morally blameworthy for feeling certain emotions.

The premise is responsible -> control

My question is why can you not link control -> not morally blameworthy to form "responsible -> control -> not morally blameworthy"? Wouldn't that equally entail the conclusion that individuals are not always morally blameworthy. Is it merely a matter that this does not appear as an answer choice?

Instead, you have to contrapose the premise to equal -control -> -responsible -> not morally blameworthy and then contrapose again to get morally blameworthy -> responsible (the answer)

Am I missing something here?

Thanks,
Ari

tomwatts
Posts: 1551
Joined: Wed Sep 16, 2009 12:01 am

Re: Linking Assumptions (PT51, S1, Q16)

Postby tomwatts » Mon May 02, 2011 1:18 am

Huh. I've never done this with conditional statements, to the best of my note-reading, but here's what it would look like if I did. (Take the ~ as "not.")

Conclusion: ~blameworthy
Premise 1: responsible -> control
Premise 2: ~control

Take a contrapositive of Premise 1, and you'd get "~control -> ~responsible." From there, you know that you want to connect to "~blameworthy", so presumably the missing link is "~responsible -> ~blameworthy," which you then take another contrapositive of to get B. Which I guess is what you were saying to begin with.

Now, you asked for someone to "explain... the reasoning behind knowing how to establish the contrapositive to link the assumption to the conclusion." Well, I knew to take the contrapositive of Premise 1 because Premise 2 was a negated version of part of Premise 1, and as soon as you see that, you know you want a contrapositive. The correct answer could have been phrased as "~responsible -> ~blameworthy" or "blameworthy -> responsible," and you don't know until you get to the answer choices that the right answer is the latter, not the former, so you just have to look for both.

I'm not sure if that's what you're asking, though.

*Ari*
Posts: 47
Joined: Sun Dec 05, 2010 1:20 am

Re: Linking Assumptions (PT51, S1, Q16)

Postby *Ari* » Mon May 02, 2011 1:48 am

That is precisely what I was asking. Thanks! So, any time that a premise is a negated part of another premise, you should invoke the contrapositive in linking the premise to the conclusion?

tomwatts
Posts: 1551
Joined: Wed Sep 16, 2009 12:01 am

Re: Linking Assumptions (PT51, S1, Q16)

Postby tomwatts » Mon May 02, 2011 3:25 pm

*Ari* wrote:That is precisely what I was asking. Thanks! So, any time that a premise is a negated part of another premise, you should invoke the contrapositive in linking the premise to the conclusion?

Yeah, as soon as you start seeing that something is a negated form of something else (whether premise, conclusion, etc.), you probably want to look at a contrapositive.




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