Putnam, Searle and Bishop: The Failure of Physicalist Computationalism

I wanted to come out of blog dormancy to write up my thoughts on what I feel is a very important argument against computationalism. The argument advances the view that there is no objective fact of the matter about which computations a physical system is computing, and if this is the case it would certainly seem to problematise computationalism (the view that what it is to be a conscious mind is just to perform the right kind of computation).

In this post I will explain the argument and some of the common responses to it. I'll reserve my own response (which is quite different from that of most computationalists) for a future post.

Consciousness is not like Photosynthesis

I've been posting some comments on Massimo Pigliucci's blog recently in defense of Strong AI, after a couple of posts attacking the computational theory of mind.

In the first, he uses John Searle's Chinese Room argument to demonstrate that a computer cannot be conscious. If you've been paying attention to this blog, you should know what I think of that argument!

In the second post, he uses an article by Jack Copeland which undermines the position of philosophers who take the Church-Turing thesis to imply that a Turing machine can do any computation performable by any machine. Unfortunately, Pigliucci seems to fail to realise that while Copeland is technically correct, the philosophers he criticises are no less so unless some very unlikely propositions turn out to be true (i.e. that the laws of physics are not computable and the brain is a hypercomputer).

But what motivated me to write this post is the same tired old argument that keeps coming up again and again in these discussions, the analogy to photosynthesis.

In Defence of Strong AI: Meta-meaning

Yesterday's post was quite long and wide-ranging, with a lot of examples etc. It focused specifically on how it might be possible to get semantics from syntax, particularly with reference to The Chinese Room thought experiment.

However I feel that I could sum up my position more succinctly by looking at the meaning of the word "meaning" itself.

In Defence of Strong AI: Semantics from Syntax

Is it possible to get semantics from syntax?

If it were impossible to get semantics (meaning) from syntax (symbols and formal rules for manipulating them) then we probably wouldn't have bothered broadcasting the Arecibo image to the universe in the hope of communicating with aliens.

Without any way to explain the meaning of this image, it seems to consist of syntax alone. Whether it could be deciphered by aliens in practice or not, it at least seems possible in principle, which seems to suggest that it may be possible in some cases to derive semantics from syntax.

The assertion that you can't, that there is no way to get from syntax to semantics, is perhaps the strongest response from John Searle to the systems/virtual mind refutation of his Chinese Room thought experiment (as outlined in my post on the topic).

Searle illustrates his point by saying that if he is in The Chinese Room and has a formal system of rules (syntax) for manipulating Chinese words, he has no way to get from this syntax to the semantics of what is being said. If he has no way to do this, then how can the system do it?

In Searle's view, the systems/virtual mind reply to the Chinese Room is just hand-waving until this is explained.

Let's see if I can attempt to do just that.

In Defence of Strong AI: The Chinese Room Refuted

It has become obvious to me that in order to fully explain my world view, I must first defend strong AI.

Strong AI is the position that it is possible in principle to have an artificial intelligence, implemented as a computing machine much like the machines we have today, which would be capable of consciousness, feeling and sensation. This is in contrast to the position of weak AI, which only claims that we could in principle make a computing machine which would merely behave as if it were conscious.

This is important not just for the ethics of how we might treat sentient computers but because it cuts to the heart of what it is that our minds actually are. If our minds are dependent on something other than simple computation, this puts limits on certain questions we might ask about our universe. For example, if computation cannot produce consciousness, then we immediately know that we cannot all be living in a computer simulation.

Firstly, I would like to point out the problems I see with some of the most popular criticisms of strong AI, starting with perhaps the most famous: John Searle's "The Chinese Room". Later I will attempt to build a positive case of my own.