> On 11 Mar 2021, at 20:58, 'Brent Meeker' via Everything List 
> <[email protected]> wrote:
> 
> 
> 
> On 3/11/2021 3:51 AM, Bruno Marchal wrote:
>> When doing theology (aka metaphysics) with the scientific method, it is 
>> better to not commit oneself in any ontological assumption at the start
> 
> That's pretty funny coming from a guy who assumes all of arithmetic exists as 
> a starting point.

The staring point is the Mechanist assumption, and not more than Darwin. Then 
the reasoning shows that very elementary arithmetic is not only enough, but 
cannot be completed, so I assume less than basically all scientists.

But your way to express this is misleading, as “all of arithmetic” is not an 
arithmetical notion, and it would need a much more string theory like set 
theory to be made precise, and this, typically is not part of my assumption.

So I assume only, beyond classical logic the non-logical usual axioms:

1) 0 ≠ s(x)
2) x ≠ y -> s(x) ≠ s(y)
3) x ≠ 0 -> Ey(x = s(y)) 
4) x+0 = x
5) x+s(y) = s(x+y)
6) x*0=0
7) x*s(y)=(x*y)+x

This is the minimal amount of things that we have to assume to make sense of 
“Digital Mechanism”. I have no doubt you do believe in them, as they are used 
in all physical theories.
I called that theory RA (Robinson Arithmetic), but his standard name in the 
literature is Q. It is a sub theory of practically any conceivable theory. It 
is even believed by formalist, as the definition of what is a formalism is as 
powerful as Q.

I can even be dispensed of classical logic, and use the (entirely given) 
following theory (of combinators):

1) If x = y and x = z, then y = z
2) If x = y then xz = yz
3) If x = y then zx = zy
4) Kxy = x
5) Sxyz = xz(yz)

I can use even weaker theory, but then they are no more finitely axiomatisable, 
and requires (like PA and ZF and most Löbian machines) some scheme of axioms. I 
might come back on the someday.

Bruno




> 
> Brent
> 
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