[from Mary Powers 9712040]
Bruce Abbott (971201.1215EST) said:
I am not suggesting that the introduction of the term >"cause" (however
defined) is necessary or fruitful when >discussing how closed loop systems
work. I can certainly >get by without it. My argument is directed against
the >notion that the use of this causal language by someone >necessarily
implies that they hold a particular notion of >causality, i.e.,
stimulus-response.
In support of this comment Bruce lists several phenomena: moving a switch
turns on a light, pulling back on the yoke moves the elevators of a plane,
smoking causes cancer, and dinosaurs went extinct because of a chain of
events set in motion by an asteroid collision.
These all, Bruce says, have "the essential feature" of cause: "a change in
Variable A (the cause) _leads to_ a change in variable B (the effect). The
term 'cause' asserts a directional property in the systematic relationship
that 'systematically related' does not".
What people are trying to get across to you, Bruce, is that the direction
A->B implies a temporal relationship: B follows A. That is what "leads to"
means. But the temporal relationships of this nature in the physical world
do not apply to control systems.
A person sitting and reading in a darkening room at sunset is perceiving the
light level all the time, and although it is dimming, he is in a state of no
error, because he tolerates a fairly wide range of brightness for reading.
Eventually the point is reached at which the level of light constitutes a
disturbance - a discrepancy between perceived and reference light levels.
The person then gets up and goes over to the light switch and flips it on.
The corrective action begins _the moment the discrepancy between reference
and perceptual signals occurs_, and the person is _in the process_ of
correcting the error _immediately_. Did the dimness of the light cause his
actions? No. It was the dimness in comparison to his reference level for
dimness (or brightness). Did the perception of dimness enter the comparator
before the reference signal got there? No. They are present simultaneously
and continuously. When they start to be different, an error signal is
generated.
If there seems to be a measurable delay in dealing with this disturbance,
such that it seems to precede the correcting action, it is because any
_visible_ action occurs later than the actual beginning of error correcting.
Moving the body involves the time it takes for for error signals to reach
the muscle control systems and for the muscles to overcome inertia.
Now as he flips the switch we are in a physical world without control
systems, and the change in the switch position does cause the light to go on
(by means we needn't go into).
_Any_ notion of causality, whether S-R, IV-DV, or whatever, when dealing
with a control system, is not only not necessary and not fruitful, but is wrong.
I could go into your other examples if you want, but not now.
Mary P.