Re: [ontolog-forum] A Question About Logic

[Thomas Johnston <tmj44p@xxxxxxx>]

John,

I will read that reference with interest. I have always been uncomfortable with the Fregean doctrine that the reference of every statement is a truth value. I'm currently rereading Chierchia and McConnell-Ginet to see if they can persuade me that Frege was right (and necessarily right).

Tom

On Tuesday, October 13, 2015 1:40 PM, John F Sowa <sowa@xxxxxxxxxxx> wrote:

On 10/13/2015 11:53 AM, Thomas Johnston wrote:
> My intuitions tell me that anyone who asserts "All dogs are renates"
> believes that there are dogs (i.e. is ontologically committed to the
> existence of dogs) just as much as someone who asserts "Some dogs are
> friendly".

That was Aristotle's assumption, and it's built into the notation,
semantics, and rules of inference of traditional syllogisms.

But the FOL rules of inference are simpler and more symmetric
with the version that is commonly used for FOL.

But there is another issue about synonymy.  With the usual FOL
rules of inference, the following equivalences are true:

    All dogs are dogs iff all unicorns are unicorns.

    All cats are cats iff 2+2=4.

One would like to say that two synonymous sentences should be
*about* the same subject.  A sentence "about" dogs should not
be synonymous with sentences "about" unicorns, cats, or numbers.

I prefer a definition of 'proposition' that takes into account
the subject matter of any sentence that states the proposition.
See http://www.jfsowa.com/logic/proposit.htm

You can adopt that definition of proposition without changing
the FOL rules of inference.  (Note:  It's my proposed definition,
but the intuitions are based on Peirce.)

John

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