# Re: What Computationalism is and what it is *not*

```
On 07 Sep 2005, at 06:35, Lee Corbin wrote:```
```
```
```Bruno writes

```
```[Hal wrote]

```
```I wouldn't be surprised if most people who believe that minds
can be simulated on TMs also believe that everything can be
simulated on a TM.

```
```
They are wrong.

```
```
Note that this is just Bruno's opinion.
```
```
No. It is Bruno's theorem :-)

```
```Hal's statement really
is true: most people don't agree with Bruno on this.
```
```

```
My sad discovery is that many people can hardly follow a deductive argumentation when it goes too much again their (not always conscious) prejudice.
```But UDA is more easy than many imagine. Also.

```
```

```
```If minds are turing-emulable then indeed minds cannot
perceive something as being provably non-turing-emulable, but minds
can prove that 99,999...% of comp-Platonia is not turing-emulable.

```
```
I don't pretend to understand this at all. You are saying
that minds (e.g. we) cannot *perceive* something as being
provably non-turing-emulable, yet minds can nonetheless
*prove* that something is non-turing-emulable.
```
```

Russell has given a good answer.

```
More generally: If you accept the use of the excluded middle principle you can prove disjunctions, A V B, without being able to prove neither A nor B. You can prove the existence of a number n having some property without being able to prove, whatever n is, that n has that property. If C represents a modality of proof, you are confusing C(ExP(x)) with ExCP(x). E = "it exits" quantifier.
```

```
```
I (very naively, of course) would have supposed that as soon
as a mind proved that X was Y, then that very mind would
have perceived that X was provably Y.

How confusing.
```
```

```
Since Godel, Brouwer ... we know that the notions of formal and informal provability are quite subtle and counter-intuitive notions. That is why modal logic, mainly through Solovay's theorem, is an incredible relief, by axiomatizing soundly and completely (at the propositional level) the logic of provability and their variants. But the simpler UDA argument gives already an intuitive feel of the oddities.
```

Bruno

http://iridia.ulb.ac.be/~marchal/

```
• Re: What Computationalism is and what it is *not* Bruno Marchal