[hist-analytic] Discussion of Aune's ETK, Chapter Two: Modus Ponens/Tollens

Bruce Aune aune at philos.umass.edu
Fri Oct 30 11:12:21 EDT 2009


I think Steve's reply to Danny on modus ponens confuses "implies" with  
an if-then connective.  "A imples B" has the form of "I(A,B)," where A  
and B are singular terms, i.e. designators of sentences, that-clauses,  
and the like.  An argument having the form of "If p then q; p;  
therefore q" would normally be said to be an instance of modus ponens,  
but as I point out there are different kinds of conditionals for which  
the English "if" might be used.  There are also "if"-statements that  
can, if Steve is right, be reasonably considered not conditionals.  I  
am not convinced by Steve's argument concerning such "if"s, but I am  
not prepared to dispute it either.  I haven't made up my mind on this  
matter.

Bruce


On Oct 30, 2009, at 10:11 AM, steve bayne wrote:

> Danny,
>
> You have two occurrences of 'Ex'; Your proof violates rules for EI.  
> You can't EI the first occurrence with the same constant as the  
> second. So the argument is not valid. I think you need to state the  
> argument in standard form; that way this should become transparent,  
> when you EI.
>
> Regards
>
> STeve
>
>
>
> --- On Fri, 10/30/09, Baynesr at comcast.net <Baynesr at comcast.net> wrote:
>
>
> From: Baynesr at comcast.net <Baynesr at comcast.net>
> Subject: Re: Discussion of Aune's ETK, Chapter Two: Modus Ponens/ 
> Tollens
> To: "hist-analytic" <hist-analytic at simplelists.co.uk>
> Date: Friday, October 30, 2009, 9:09 AM
>
>
>
> #yiv188251479 p {margin:0;}
>
>
>
>
>
>
> Danny,
>
> Sorry Danny, I just don't understand much of this. For example, you  
> bring in Davidson, but I see no reason to: where are the event  
> variables for example, if you are taking a Davidsonian approach?
>
> It is obvious the argument is valid IF the first premise is a  
> conditional. I argue against this. You ignore the argument. I don't  
> mind that. But if, f as you say the premises are inconsistent, then  
> of course anything follows and modus ponens needn't enter the  
> picture at all.
>
> Elsewhere, I've argued that Davidson is wrong on the treatment of  
> adverbials, in particular across prepositional phrases where the  
> verbs are causal. Can't digress into Davidson, now.
>
> Of course Bruce likes what you say, but I don't think his argument  
> (or yours) rules out seeing that the premise (first) is no  
> conditional at all etc. In short, you've ignored my argument and  
> substituted reasons for thinking the argument is invalid. I agree it  
> is invalid but it is not a modus ponens, tollens, argument etc.
>
> I think the question "What is modus ponens?" is somewhat rhetorical.  
> It's a rule that says that if you have 'p implies q' and 'p' then  
> you can derive 'q'. No mystery here, OR we are in for a revolution  
> in logic, which I doubt




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