[From Bill Powers (931126.0730 MST)]
Gavan Lintern (931125) --
I'm puzzled by your statement that "dynamic systems do not
control." This would come as a great surprise to several
generations of control-system engineers and life scientists who
have analyzed the dynamics of both artificial and natural control
systems of countless kinds. Are you using this term in some
special way? In my understanding, a dynamic system is simply a
system in which dynamics plays a part -- that is, any system that
is not static. A control system, because it involves variables
that change through time, is automatically a dynamic system as I
understand the term.
Why do the ecological folks de-emphasize control and assume it is
not central to behavior? I don't understand how they can "de-
emphasize" a natural phenomenon. Do they understand what control
is, as control engineers and theorists study it? Perhaps you
could tell me what the ecological folks mean by the term control;
it could be that we aren't talking about the same phenomenon.
When you brought up the example of a falling object at terminal
velocity, you were illustrating the concept of a balance of
forces. I followed your lead, and showed how control could appear
in this situation, so that one of the forces was varied to
produce and maintain a intended outcome (the photographer falling
at the same rate as the stunt diver) in the face of disturbances
(variations in the falling rate of the stunt diver). This is
certain a real example of control -- millions of people have seen
this happening on TV. I don't understand why you now want to
switch to the topic of the gaits of horses without resolving the
issue I brought up in the context of your original example.
However, if you really want to talk about gaits, I'm willing. How
do you you explain the behavior we call "trotting?"
I am familiar with the work of Kelso, Turvey, Fowler, and others,
although not extensively so. "Coordinative structures" and
"equations of constraint" are unable to explain control
phenomena, although control-system analysis can readily explain
the phenomena of which they speak. For some reason, they are
singularly uninterested in discussing the control-systems
approach, preferring to make up their own ideas of what control
theory is about. This has led all of them to make some rather
silly statements about control systems in print. I've more or
less given up on them.
I suspect a real problem for many with the dynamical systems
approach is that of intentionality. I do not agree that HPCT
or anyone else deals with intentionality in a satisfactory way.
This is a startling statement, as PCT and HPCT are centrally
concerned with intentionality, and indeed, in my opinion, offer
the first coherent explanation of intentional or purposive
behavior. You can imagine, therefore, that I have a serious
interest in learning why you make this statement.
In what way does HPCT fall short of handling the phenomenon of
intentionality? If you don't mind my asking, how do you believe
HPCT approaches this subject, and what explanation do you believe
HPCT offers? It's possible that the story has been garbled in
transmission, so before any extended discussion it might be a
good idea to establish what each of us means to be talking about.
It might be even more important to make clear what the phenomenon
under discussion is: what is your conception of intentional
behavior? That is, how would you say that one recognizes
intentional behavior when it's going on?