On Sun, 23 Jul 2006 23:24:56 -0400, firstname.lastname@example.org wrote:
> > >Lester Zick wrote: >> >> Virgil wrote: >> >> > Lester Zick wrote: >> > >> >> email@example.com wrote: > >[...] > >> >> >> >No. P may be false and validly imply true Q. >> >> >> >> >> >> I don't follow this. If P is false then any Q demonstrated of P is >> >> >> false too. >> >> > >> >> >Let P = Margaret Thatcher is a man, and all men are politicians. >> >> >Let Q = Margaret Thatcher is a politician. >> >> > >> >> >P is false, and validly implies Q, which is true. >> >> >> >> Well sure but you're using compound predicates which are false to >> >> begin with > >I think you mean "compound sentences" or "compound propositions".
No. I mean compound predicates.
>> >> and don't really imply Q except to the extent they're >> >> false. > >No. The validity of the argument does not rest on the premise being false.
The invalidity of the argument does.
>> >> If I were simply to say "Margaret Thatcher is a male politician" >> >> the effect would be exactly the same. > >This is correct. "Margaret Thatcher is a male politician" follows from >"Margaret Thatcher is a man, and all men are politicians".
Not exactly. It's the other way around.
>Futhermore, the inference "Margaret Thatcher is a male politician, >therefore Margaret Thatcher is a politician" is a valid inference, >with a false premise and a true conclusion, and the validity of >the inference does not rest on the falseness of the premise.
I don't exactly follow where you're getting all this. It sounds like some kind of syllogistic word game to you. You have a false conclusion: "Margaret Thatcher is a male politician". Period. Nothing necessarily follows from anything except the fact of falseness. So wherever you think you got the conclusion is immaterial. It doesn't necessarily depend on whatever you think because it's wrong.
>> > Not to anyone who knows anything about logic. > >Just because a lot of what Lester says is wrong, doesn't mean >everything he says is wrong. Don't let him stampede you into >pre-emptory dismissal of everything he says, as tempting as >that might be.
Oh hell. Go right ahead and let me stampede you into peremptory dismissal of everything I say. It's pretty obvious the mathematikers around here are about as lazy and stupid as their faith based systems of math would suggest.
>> But apparently to anyone who knows nothing about truth. >> >> >> The proposition is just false. > >True. The proposition P is false, and "Margaret Thatcher is >a male politician" is false. > >> >> Q may or may not be true > >Q is true.
Jesus who cares? Just because you mix up some middle terms (I should say muddle terms) with the same spelling? Obviously you don't get your incorrect conclusion by stringing random clauses together. This is one of the really stupid problems associated with syllogistic inference. Q may be true but Q is not true of P because P is false. In other words if Q is true (and it is) it isn't because it's a component of P.
>> >> but not because P is false. > >Correct. > >> >It is the compound proposition "If P then Q" whose truth is under >> >consideration, and for the P and Q given, "If P then Q" is true.