Congress

Congress

(Hope this link works)

Implied premises/conclusion anyone?

Reflexive Logic

            I know that I blogged something similar to this before, but I have an hour commute that includes a lot of NPR and these things keep popping up.  The story had something to do with a recent effort in Germany to piece back together old shredded Stasi files from the Soviet days.  Again, I apologize that I don’t remember the details.  But they interviewed a young woman who was involved in the project and she explained her participation thus:  “If this work were not important, I would not be doing it.”

~Iè~D

            This seems like a perfectly reasonable thing to say, but my logic reflex kicked in and I immediately tried to discern her implicit premise and conclusion.  Is this an example of modus tollens, or the fallacy of denying the antecedent?

P:  ~Iè~D

P:  D

C:  I

            This works (with MT, DN), but seems strange:  “If this work were not important, I would not be doing it.  But I am doing it.  So, it must be important?”

           

            It seems more natural to say it the other way:  “If this work were not important, I would not be doing it.  But it is important.  So, that’s why I’m doing it.”

P:  ~Iè~D

P:  I

C: D

            But, alas, this is a clear case of FDA! Blasted logic! Perhaps the first formulation is not so strange after all, but it threw me for a loop.

Wednesday's Challenge

So this is my best guess at the problem that we were struggling with in class on Wednesday.  I’m not sure if I’m using Material Implication correctly, but it seems to work as far as I can tell.  Also, I know that it is in the front cover of the book, but I did not think that we had actually been given MI as a rule of inference yet.  Can anyone point me to when that happened?

1.  ~(PçèQ)                                    Prem. / Therefore: ~(QçèP)

2.  ~[(PèQ) & (QèP)]         1, BE

3.  ~(PèQ) ∨  ~(QèP)         2, DM

           

            4.  QèP                      Supp. CP

            5.  ~(PèQ)                 3,4, DN, DS

6.  (QèP) è~(PèQ)           4-5, CP

7.  ~(QèP) ∨ ~(PèQ)          6, MI

8.  ~[(QèP) & (PèQ)]         7, DM

9.  ~(QçèP)                        8, BE, QED