Re: An argument against modus ponens

Mitch 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. So "if P" requires the consideration
of another element or object through which a truth value may be
ascertained.

I don't know about 'requires', but let's just allow that for the
moment.

'Requiring' was a suggestion to our logical commuters that unless they wish to travel a la pieton, they had better make enquiries if they'd rather catch the bus. I thought the term was ok because it attended to an anthropomorphic P.

COndieration of another element, which I suppose you're
calling R. I'd say that this R is some sort of context for knowing
unspecified things about P. OR rather that R -is- the specification
allowing one to know things about P. Does that sound right?

Yes, it sounds right, but I would rather R be an object and not a context for objects. I'm assuming that R and P are in the same context.

If we eliminate the ontological and existential status with
which the term "if" baptises its objects,

May be, or rather having P be the antecedent of a conditional -
removes- the need for caring about ontology (that's the beauty of
conditionals/subjunctive, not having to worry about ..ahem..reality...
just -suppose- something is the case. Just about as useful as the
concept of variables (where you don't care about all sorts of
irrelevant properties of an object, you allow -anything- (satisfying
the given properties) to be instantiated without bothering to actually
do so).


then modus ponens reduces to

P and R, then Q
P. Therefore, Q

Hm, I think you meant to say

"P. Therefore, in the context of R, Q."


And eliminating the subjective "then" and "therefore" we have modus ponens
P and R and Q
P and Q

Whatever you said and meant above, this just doesn't seem to fit at
all. 'then' means 'and'? I think you're throwing away quite a bit in
that substitution (or really substituting totally inappropriately).

My post was written in one sitting. "P and R, then Q" was the half-completed argument to the fully converted "P and R and Q". (Or P, Q, R). I was doing it in stages, but the presence of stages doesn't entail steps in the argument here.

CONCLUDING
Plainly, modus ponens is invalid.

Modus Ponens is complex. Or rather, it is not. It is often the only
inference rule ever needed (both technically and informally). I think
that maybe you wanted to say that MP is 'unsound', or 'doesn't take
into account blah blah lblha'. 'Invalid' is pretty much not really
applicable here.

God preserve me from the myriad of terms that continue to plague me from philosophy and elsewhere. Invalid and unsound are those sort of words that no matter how many times I look them up, they just don't take root. Other words include empirical, a priori, and many others.
So here is the John Jones distinction between invalid and unsound: - no distinction - just "buggered up, right, good and proper". Yes, that's it, modus ponens is buggered up, right good and proper. It seemed like it from the off. It was because of this observation that I could make an investigation to find out why.

The truth value operator "if" ushers
in another object, while "P." does not.

Possibly. I think you can say things without referring to context.
But, again, for argument's sake, we'll supose that 'if' requires a
context.

Context is a problem of course. Context brings in a world baggage. Can P exist on its own? But I am arguing for a logic that can take care of itself, a logic that says no more than it says. P says P, no more or less. If "P" (and not "if P ...") is a logical object then it is indifferent to context.

[A problem for me here is that elsewhere I said that "if" statements usher in truth values. So if I say this: "if P is a logical object", the it would seem to deny me the option of presenting only P, as "if P" implicates R, even if the context for R is not one that presents R as a logical object. The only way I can break the link between P and R is by saying that "if" statements usher in either commensurables or incommensurables, where only commensurables usher in truth values. So let us say that "if P is a logical object" ushers in R where R is INncommensurable to P, ie. in a different context, and so does not usher in truth values (truth values are intra-contextual). But then it seems that contexts are indeed necessary for logical objects, whereas, above, I said that they were not. I can get around this by saying that contexts are not 'different' to each other, but incommensurable. There are no external contexts. This would not quite allow me to say, as I did above, that logical objects are "indifferent" to contexts, as I still need to distinguish logical objects that are intra-context from those that are extra-context - I must still treat extra-contextual logical objects differently to intra-contextual logical objects. I must address that problem..]

The argumentative form may be
correct, but modus ponens describes two different object events - "P and
R" and "P".

DISCUSSIONS
Modus Ponens doesn't get off the ground - it describes two different
object events. But let's take a closer look at its subjective or
existential argumentative form which may yield something of worth.

Modus ponens
If P, then Q = P. Therefore, Q

This is hard to read. I'm guessing you're saying:

"If P, then Q" = "P. Therefore Q"

Is that right?

Yes.

If so, then...

Which reduces to
If, then = then, therefore

you're saying "If,then" = "then, therefore" (whatever either of those
might mean, it's difficult to figure out).

I was rushing it, but its ok I think. "If,then" = "then, therefore" takes the term "then" to be shorthand for a presentation of an element, thus: "then Q" = Q" (and "P." = P) So "If,Q = P,therefore".

It's awkwardly presented though, ... written in one sitting.

This says that existential possibility is equivalent to existential
reality when each identifies the same object.

No, I don't think so. The antecedent of a conditional is, in what I
think is your language, a fantasy accepted momentarily to be real. So
not -equivalent-, just a temporary acceptance.

It should not matter what P is, or its existential occurences:

If P refers to the same object in any existential occurrence of P, then, the existential possibility of P is equivalent to the existential reality of P when P identifies the same object.

It also says that
reference to an object (which is the way that "possibility" presents its
objects) is equivalent to the object itself.

That follows (vaguely) from your previous statement but your previous
statement is not right.

Possibility, or truth values, refer to an object, whereas a presentation of an object is the object itself and does not refer. So "if P" refers to P, whereas "P" presents P. The latter, "P", "presents" P because we are using a logic that must look after itself - where what you see is all you get.

Modus ponens, in that case, is a convoluted form of the transcendentally
real notion that reference and self-reference are the same.

OK. I see how that follows in another (again vague) step from the
previous statement.

The logical object P supports itself.

Accordingly,
(Godellians take note) any proof which employs modus ponens and which
also relies on the distinction between self-reference and reference is
scuppered from the outset.

Very provocative.

I'm on holiday.

That -doesn't- follow from your previous statements.
It refers to reference and self-reference in a vaguely similar way to
your previous ones, but that's about it. Just vague. How does
something that relies on the self/non-self reference necessarily void
the use of MP -even if- MP doesn't distinguish them? You need to give
an example where self- and non-self-reference are used in an attempted
proof where it messes up an MP inference.

Maybe for another time, its late now. But just for now, a presentation of P and a referral of P are not equivalent presentations of P unless they identify and present the same object - but then a referral cannot present an object, it identifies one.

Anyway, MP doesn't pose problems with respect to reference/self-
reference. If it did, then it still doesn't follow that other self/non-
self references will be messed up by the use of MP.

Mitch
.

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