[From Rick Marken (940903.2300)]
Bruce Buchanan (940903) --
I'm controlling for good health care for everyone at the lowest
possible cost. I am not controlling for the means used to achieve it.
The trouble with most general statements of this kind is that they are
sufficiently imprecise that no one can resonably disagree.
Let me try to be more precise. When one controls a variable (say
"quality of health care") the actions (means) used to keep that variable
in its reference state must vary in order to compensate for changes in
the specification of the reference state for that variable, changes in the
effects of disturbances to that variable and changes in the effects that
the actions themselves have on that variable. If the actions themselves
are under control, it will be impossible to vary these actions, as
necessary, to keep the controlled variable (quality of health care) under
control. This statement is "general" in the sense that it is _always_ true
in all control situations. It is true whether the perception being
controlled is the position of a cursor on a computer screen, the quality
of one's relationship with one's spouse or the quality of health care in
the US. It is embodied in one of the two basic "laws" of perceptual
o = p* - d
which says that, in order to keep a perceptual variable, p, matching a
reference variable, p*, the actions (o) of the system doing the
controlling must be directly proportional to variations in the reference
variable, p*, and negatively related to variations in the net disturbance,
d, to the controlled variable. If o (the means used to control p) is
itself under control, then it will very likely be controlled at a value
that is not equal to (p*- d). Since the only way to control p is to
keep o nearly equal to (p*- d), control of o would prevent control of p.
This is all just a fancy way of saying that, if you have a preferred way of
holding the handle in a tracking task, you won't be able to keep the
cursor on the target; you can't control the cursor and the means used to
control it (handle position) at the same time.
In addition, while it is hardly conceivable that the ends do not control
for at least some possible means
I take this to mean that p* (the end to which p, the controlled variable,
is constantly being brought) influences (not controls, of course) the
actions involved in the control of p, and, indeed, this is true. Actions
are determined by both p* and d, though d is by far the main influence
on actions when p* is constant.
The point of such questions here is to illustrate the need to recognize
that vaguely stated general principles are just that.
I hope I have stated the general principle less vaguely. Again, the
general principle is that the actions (o) that are involved in the control
of a perceptual variable (p) must be free to vary (they must be
uncontrolled) in order to keep p (the controlled variable) in a (possibly
varying) reference state, p*, against disturbance, d.