Re: An argument against modus ponens
- From: John Jones <jonescardiff@xxxxxxx>
- Date: Thu, 04 Sep 2008 22:14:12 +0100
george wrote:
On Sep 3, 4:54 pm, John Jones <jonescard...@xxxxxxx> wrote:Modus Ponens:
If P, then Q.
P. Therefore, Q.
The "If" announces a truth value.
No, it doesn't.
The prior parameters of the discussion announced that P and Q were the
kinds of things that have truth values. The "If" by itself DOES NOT
do ANYthing:
it is, in this context, INSEPARABLY bound to the "then". The "if"
and the "then"
TOGETHER name ONE well-defined binary boolean function. There are 16
such functions.
Every speaker is basically entitled to spell and articulate them in
ANY mode she damnwell
pleases, AS LONG as these (and other) conventions are spelled out in
advance.
You accept, do you not, that the function "if.." (and/or the function "then..") immediately (if you like) launches us into a context where "if P" yields P as true or not true. And, as it happens, if P is true, then Q follows.
But my point is that whether Q follows or not, or even whether "then" always follows "if", or is a necessary adjunct to the grammar of "if", an "if .." proposal sets up a context of truth and falsehood. And notions of truth and falsehood are not required in the presentation "P." (i.e. P alone).
If you don't agree with this summation, and you think that truth values are configured by P and Q in modus ponens, then doesn't your position reduce your modus ponens to this:
P, then Q.
P. Therefore, Q.
Here, "then" is simply a synonym for "therefore".
And in fact, I would argue for this. But as I hoped to have pointed out, if we want to keep contingency (and truth values) in our logic, then we must introduce another term ('R' as I called it), but that this is not brought in by P or Q alone.
So "if P" requires the consideration of another element or object through which a truth value may be
ascertained.
Yes, if/then, like And, like Or, and like any of the other 13 binary
boolean functions, is a binary
boolean function, and it does assign/ascertain a truth-value result,
given truth-value arguments.
If we eliminate the ontological and existential status with
which the term "if" baptises its objects,
Well, that would be STUPID, wouldn't it?
This whole thing is ABOUT true and false, isn't it?
It's also ABOUT statements that CAN BE true and false, isn't it?
To eliminate the ontological or existential status of truth, falsity,
P, Q, or
boolean functions WOULD JUST BE STUPID in this context.
It ought to go WITHOUT saying that we are presupposing the existence
of these things.
Yes. But I think that because logic sees these things as part of logic, it sees no need to acknowledge hidden elements.
.
- Follow-Ups:
- Boolean variables are necessarily boolean
- From: george
- Re: An argument against modus ponens
- From: george
- Boolean variables are necessarily boolean
- References:
- An argument against modus ponens
- From: John Jones
- An argument against modus ponens
- Prev by Date: Re: An argument against modus ponens
- Next by Date: Re: how to prove E!x(Fx & Gx) -> Ax(Fx-> Gx)
- Previous by thread: Re: An argument against modus ponens
- Next by thread: Re: An argument against modus ponens
- Index(es):
Relevant Pages
|
