FOM: Alice, Bob and Carol
wiman lucas raymond
lrwiman at ilstu.edu
Tue Apr 9 00:01:04 EDT 2002
> 7. So, isn't that all there is to say about number?
In some senses, yes, that is all there is to say about a number. A
is an intuitively obvious idea, something that even a chimpanzee can
Chimpanzees certainly don't understand Fregean ideas! The point is that
those who worked on foundations in 19th century abstracted the
obvious ideas of "counting", "set", and "identity" to a rigorous
system. These systems don't always agree with reality, but are
Take the idea of continuity. What is a continuous function? Well,
obvious: it's a function whose graph can be drawn without breaks in it.
That's fine, of course, until you want to start proving things about
functions. One needs to start working with continuity at a point, and
that nature. One eventually comes up with the standard "epsilon-delta"
of continuity. But this notion, while it seems intuitive, has
consequences. For example, there are functions which are discontinuous
rational value, but continuous at every irrational value. That's very
inuitive, but it's an *abstraction* of our real experience of drawing
It's not reality.
> If just saying a bunch of objects are all different from each other is
> enough to say they have a number, why not stop right there?
As I said, the idea of "number" is not a difficult one to grasp. The
is how can mathematicians work with them? If we just assume at the
numbers are intuitively obvious, then what is a proof? We need to state
assumptions about them at the outset, and then prove things based upon
assumptions. The Peano axioms aren't numbers--they abstract numbers
> To sum up a very simple argument, we can communicate information about
> many things there are without communicating any information whatsoever
> the sort that Fregean or neo-Fregean number says is essential to our
> about number, or about number "itself".
Yes, because ordinary language is much less precise than mathematical
Our standards for indentifying "three-ness" in everyday language are
than Peano's or Frege's. This is fine, but mathematicians need to be
formally study these objects.
> Moreover this information, if correct, reflects the way things are, so
> nothing else is relevant to the *fact* that there are a certain number
>From which I conclude all the Fregean stuff is absolutely irrelevant
>to our ideas about number, or to facts about it.
Whoa, that's quite a leap. I find it very dubious to say that Peano
has nothing whatever to do with number theory (the facts about numbers),
number theory definitely relates to the real world.
Note that I'm not saying that mathematicians necessarily start out with
axioms, and work from there. Actually, I doubt that any number
However, if one is to undertake a logical study of number theory, one
start with an axiom system. Without the Peano arithmetic axioms, it
be possible to prove Goedel's incompleteness theorem. This certainly
something signicant. Perhaps not about the immediate notion of
but about the limits of human reasoning.
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