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

steve bayne baynesrb at yahoo.com
Fri Oct 30 10:11:06 EDT 2009

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.

--- 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;}

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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