[dragonwriter]

> This line of argument does achieve the goal of making it trivially true under the definitions given that the brain is a computer, but it seems to me it robs the assertion of insight

I think, rather, it reveals the fundamental lack of clarity of the contrary position.

> e.g., the brain is computer because everything is a computer, including the nearest rock, since it's also a physics-governed system.

Right. But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems. The AI-is-impossible position boils down to the argument that the mind is not like all other physics governed systems, though it tends to waffle and hedge and bob and weave around that point rather than coming right out with it. Pointing to Turing equivalence and the apparent computability of natural phenomena forces the AI-is-impossible-because-the-mind-is-not-the-kind-of-thing-a-computer-can-simulate argument to come straight out and either (1) reject the universal computability of physical systems, or (2) reject the mind as a physical system.

It still, of course, leaves plenty of room for the proposition that AI is possible but really quite hard.

[coldtea]

>But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems.

Actually it sounds especially difficult.

A crude approximation (simulation) at best.

Nothing like a full rock, with its full interactions with its full environment (that might need simulating the whole universe), and with oversimplifying most of its properties (molecular interactions, heat dynamics, etc).

Now make it a "wet rock" and we're even further away (and I wont even dare ask for mold on it or anything, much less living micro-organisms)...

[wwweston]

> But no one is questioning the ability to build a computer that simulates the behavior of a rock; or most other physics-governed systems.

I'm willing to make that challenge: a complete simulation of rock sounds like a formidable problem to me, one I'm not at all certain is within state of the art.

Particularly if (as we're generally imagining when we're talking about simulating brains) we're asking the simulation to be able to stand in for its analog as part of a process-chain connected to a non-simulated situation.