From [Marc Abrams (2004.10.27.1407)]
For those who had my old address blocked, I’m sorry for this inconvenience . My old carrier is going out of business so I’m temporarirly using my daughters AOL account.
For those who cannot or do not want to read my posts I wish you a good day. 
I have often wondered what the difference was between SD and PCT. Both theories originated from ideas in Servo-mechanism control theory and in a conversation I had with someone who was associated with the meeting I helped set up between Jay Forrester and Bill, intimated that the meeting went well and that there was no difference between the two.
I found this to be extremely odd because SD models do not adhere to the PCT control paradigm of the focus of control of the input rather than the output.
Part of my answer is found in; Principles of Systems, Jay W. Forrester, 1968
···
Pg 4-1; System Structure
I. The closed system generating behavior that is created within a boundry and not dependent on outside inputs.
A. The feedback loop as the basic element from which systems are assembled.
1. Levels (stocks) as one fundamental variable type within a feedback loop.
2. Rates (or policies) as the other fundamental variable type within a feedback loop.
a. The goal as one component of a rate
b. The apparent condition against which the goal is compared
c. The discrepency between goal and apparent condition
d. The action resulting from the discrepancy
4.1 Closed Boundry
We are interested in systems as the cause of dynamic behavior. The focus is on interaction within the system that produces growth, fluctuation, and change. Any specified behavior must be produced by a combination of interacting components. Those components lie within the boundry that defines and encloses the system.
So, from this little excerpt its obvious that Bill Powers and Jay Forrester have the same exact ideas on how and why behavior takes place.
Bill published a paper in the SD journal a number of years ago.
Maybe someone can tell me why there has been no collaboration between SD and PCT?
I bet this is the very first time both Rick and Bill (if he was so bold as to read this post) have seen this from Jay Forrester.
Both Bill and Rick extolled the virtues of iscientific inquiry. Why was this NOT done with SD? Why did Bill publish in the SD journal if he felt it was a waste of time?
Maybe someone can enlighten me as to the reasons why PCT provides a better structure for studying human behavior aqnd cogniition than SD?
Since this forum is not very fond of foreign ideas, if anyone is interested in the SD->PCT connection you can contact me privately, there is much work to do.
Marc