Re: An argument against modus ponens

george wrote:
On Sep 19, 11:01 pm, John Jones <jonescard...@xxxxxxx> wrote:

"It's raining" has a truth-value!

Ridiculous. And you know it. Logic isn't grounded in the weather forecast. Logic can't check the weather. "It's raining" has no truth value.

"John Jones is not my real name"
has a
truth-value! Sentences USUALLY have truth-values if they are in the
indicative mood
(interrogative, imperative, and exclamatory sentences may fail to have
truth-values,
but those are all FROM NATURAL language, AND WE ARE TALKING ABOUT
FORMAL


Then kindly follow your own example and remember that we are talking about formal languages. Unlike our natural language conditions, formal languages do not have access to local weather forecasts.

Put another way, what exactly is this thing that can be
different things?

Nobody ever said anything could BE different things.
Things can only be what they are.

Thankyou. Things can only be what they are, without truth or falsehood. So you can't speak of P being false. Why? Because a false P assumes both P and R.

WE are NOT talking about
words in the natural-language sense, OR about the things those words
refer to. WE ARE TALKING ABOUT *STRINGS*.
We are talking about SYMBOLS.
We are talking about FINITE LISTS OF CHARACTERS.
THOSE are our atomic building-blocks around here.

Then follow your own example and remember that. Strings etc represent themselves. They don't tell us what the weather might be doing, whether 'it's raining' is false or not.

We may also be talking about natural numbers and
THE TWO truth-values as atoms,

Suggestively unintelligble. Ambiguous at best.

but because these are abstract,

That's no explanation. That's a logical wound-plaster.

it is entirely allowable to REPRESENT these AS STRINGS AS WELL.
The number is not (necessarily) the SAME as its numeral, and the
truth-
value is not the same as the symbol or string that names it, BUT THEY
MIGHT AS WELL be; they are both abstract.

That is airy-fairy land. I'm surprised you've gone there. Peter Pan says that numbers are numerals when they're abstract. I suppose Captain Hook has been swallowed by the crocodile by now.

And I repeat, this simply is not a problem in the context of a formal
language.

That's sad. It's sad that someone out there thinks that numerals and numbers are all alike in the far-off, auto-put-right land of mathmatico-logic.

The problem is 1 level lower when you have to somehow convey which of
16 binary boolean functions some string is supposed to "mean" or point
to.
But that is simply NOT A PROBLEM for MOST people; you just handwave
and
keep going. The fact that the argument-lists for these functions are
known to
be two-element lists of truth-values (and the result is also a truth-
value) means that
ANY number of various string-representations of them WILL DO.

So now you are saying that there are lots of true and falses. Before, you were speaking of just 'true and false'.
.