Rifka: We do not need to stop and ask for directions. We would not need to do that unless, of course, we were lost.C...

Batman December 3, 2013

Need your help!

First, I don't know what the implicit premises are in Rifka's statement, which seems explicit premise to me. Second, are there more than one implicit premise in Rifka's argument?

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Mehran December 4, 2013

Let's take a look at Rifka's argument first. Rifka's conclusion is: "We do not need to stop and ask for directions (aka "SAFD")." Why? Well the general principle Rifka sets forth is: "We would not need to do that unless, of course, we were lost (aka "L")."

We know unless introduces the necessary condition and the negation of the other part of the statement is our sufficient condition so this statement would be diagrammed as follows:

SAFD ===> L
not L ===> not SAFD

Rifka's conclusion is that we do not need to stop and ask for directions, i.e. not SAFD. Rifka's implicit assumption here is that we are not lost because that would invoke the sufficient condition of our general principle's contrapositive and allow us to properly conclude that we do not need to stop and ask for directions.

Craig clearly disagrees with this implicit assumption because he states, "The fact that we are lost is precisely why we need to stop." As such, Craig believes we are lost and this is why we need to stop and ask for directions.

Notice answer choice (B) states exactly this, i.e. "deny one of Rifka's implicit premises (i.e. we are not lost) and thereby arrive at a different conclusion (i.e. we need to stop).

Hope this helps! Please let us know if you have any other questions.

Batman December 4, 2013

Thanks a lot!!!!^^

RyanSpencer May 3, 2019

I'm not sure if I understand... so the contrapositive is the implicit premise?