On 05 Oct 2011, at 17:33, benjayk wrote:
OK. We don't have to use numbers per se, but notions of more and
On 10/4/2011 1:44 PM, benjayk wrote:
Bruno Marchal wrote:
This is a bit a technical question, which involves logic. With
Bruno Marchal wrote:
But then one 3-thing remains uncomputable, and undefined,
namely the very foundation of computations. We can define
terms of numbers relations, and we can define number relations
+,*,N. But what is N? It is 0 and all it's successors. But
are successors? They have to remain undefined. If we define 0
number, natural number remains undefined. If we define 0 as
successor, successor remains undefined.
All theories are build on unprovable axioms. Just all theories.
Most scientific theories assumes the numbers, also.
But this makes not them undefinable. 0 can be defined as the
natural numbers, and in all models this defines it precisely.
But natural *numbers* just make sense relative to 0 and it's
because just these are the *numbers*. If you define 0 in terms of
numbers, and "least" (which just makes sense relative to
defined them from something undefined.
So I ask you: What are natural numbers without presupposing 0
logic, 0 and s can be defined from the laws of addition and
multiplication. It is not really easy.
It is not technical at all. If you can't even explain to me what the
fundamental object of your theory is, your whole theory is
I'd be very interested in you attempt to explain addition and
without using numbers, though.
It's easy. It's the way you explain it to children: Take those red
blocks over there and
ad them to the green blocks in this box. That's addition. Now
different pairs of one green block and one red block. That's
Anyway, we get the same problem in explaining what addition and
multiplication are in the absence of any concrete thing of which
be more or less, or measurements that can be compared in terms of
Yeah, but it remains to be shown that platonia is more than just an
Bruno Marchal wrote:
But to get the comp point, you don't need to decide what numbers
you need only to agree with or just assume some principle, like 0
not a successor of any natural numbers, if x ≠ y then s(x) ≠
I agree that it is sometimes useful to assume this principle, just
sometimes useful to assume that Harry Potter uses a wand. Just
things like that.
can usefully assume some things in some contexts, do not make them
So if you want it this way, 1+1=2 is not always true, because
other definition of natural numbers, were 1+1=&.
It's always "true" in Platonia, where "true" just means satisfying
axioms. In real
life it's not always true because of things like: This business is so
small we just have
one owner and one employee and 1+1=1.
haven't yet seen any evidence of that.
Bruno seems to justify that by reductio ad absurdum of 1+1=2 being
on ourselves, so 1+1=2 has to be true objectively in Platonia. I
that argument. If our mind (or an equivalent mind, say of another
with the same intellectual capbilites) isn't there isn't even any
1+1=2, because there is no way to interpret the meaning in it.
Would you say that if the big bang is not observed then there is no
Why would it be different for "1+1 = 2"?
I think that you are confusing " "1+1=2" is true" and the fact that
We need a subject to asses the truth of the string "1+1=2", but no one
is a priori needed for the fact itself to be true or false, a priori.
It only seems
to us to be true independently because we defined it without explicit
reference to anything outside of it. But this doesn't prove that it
independently anymore than the fact that Harry Potter doesn't
mention he is
just a creation of the mind makes him exist independently of us
This does not logically follows, and beyond this, it is obvious that
Harry-Potter land does exist in any "everything" type of theories.
Indeed with comp, or with other everything type of theories, the
problem is that such fantasy worlds might be too much probable,
contradicting the observations. The mere existence of them cannot be
used in a reductio ad absurdum.
We don't know what reality is. We are searching.
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