Re: Solidity is degree of justification (was: Mirror neurons at autopsy)

On 24 Dec 2012, at 09:07, Bruno Marchal <[email protected]> wrote:

> 
> On 23 Dec 2012, at 20:13, David Deutsch wrote:
> 
>> an important (and  
>> unrelated) philosophical error, the one that is currently called  
>> 'justificationism', namely that knowledge is that which can be  
>> justified as true, or likely to be true, etc.
>> 
> The Theaetetus theory of knowledge is "justified *and* true", not  
> "justified as true", as this is impossible.

I stand corrected.

> The nature of the "and" is let unknown, and with comp can be shown  
> unknowable.
> 
> It gives an instance of the "classical theory" of knowledge, which is  
> the theory that knowledge is well described by the modal logic S4,  
> that is, with Kp = I know p,: Kp -> p, Kp -> KKp, K(p->q) -> (Kp ->  
> Kq); with the modus ponens, the classical tautologies, and the  
> necessitation rule: p => Kp.

I (and, I think, Popper) would say that the attribute expressed by that predicate K cannot be possessed (or usefully approximated) by a physical object with respect to scientific theories p, even though it can be defined formally. Hence he uses the term 'knowledge' to refer to a different attribute, one which does not require a knowing subject but which, apart from that, corresponds at least as closely to the commonsense meaning of the term as K does.

In my view, formalising *that* conception of knowledge is a task for the future, equivalent to achieving Artificial Intelligence.

-- David Deutsch