Brent meeker writes (quoting SP):

> > Every physical system contains if-then statements. If the grooves on the 
> > record were different, 
> > then the sound coming out of the speakers would also be different.
> That's not a statement contained in the physical system; it's a statement 
> about other 
>    similar physical systems that you consider possible. You could as well 
> say, (print 
> "Hello world.") contains an if-then because if the characters in the string 
> were 
> different the output would be different.

I don't see how you could make the distinction well-defined. Consider the 
following two programs:

input: x
if x=1 print "hello"
if x=0 print "goodbye"
data: 1


print "hello"

As written, program (a) will print "hello" just as consistently as program (b). 
It looks like program (a) has a conditional in that if the 4th line were "data: 
0" it would print "goodbye". However, program (b) would also print "goodbye" if 
that string were substituted for "hello". Both programs do the same thing, and 
both would do something else if the programmer intervened and changed them. In 
(a) the code is separated into "program" and "data" but as you pointed out 
recently there is no real difference between these. Subroutines within a larger 
program could be intelligent entities interacting with a virtual environment 
with no input from outside the program in the same way as intelligent entities 
within the real universe interact with the environment with no input from 
outside the universe.

It's worth standing back at this point and looking at what a computer + program 
+ data really is: a collection of plastic, metal, and semiconductors assembled 
in a specified way which has no choice but to follow the laws of physics. The 
if-then statements amount to a particular physical configuration such that 
stimulus x will make the computer behave one way while stimulus y will make it 
behave in a different way. This is not fundamentally different to saying that, 
for example, a car is configured so that it will turn left or right depending 
on which way the steering wheel is turned. In both situations, dumb matter 
blindly follows the laws of physics. The difference is in the details, 
complexity and intended purpose of each device; it is not that the computer 
interacts with its environment and handles counterfactuals while the car does 

Stathis Papaioannou
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