This file is posted every month to CSGnet.


          Prepared by Dag Forssell with Gary Cziko
                  Updated December 26, 1995

This is an introduction to Perceptual Control Theory (PCT), and the
discussion group CSGnet. CSGnet is listed on Usenet as the
newsgroup "bit.sci.purposive-behavior." This introduction is
posted at the beginning of each month for newcomers to CSGnet and
the newsgroup.

A complementary, more detailed "PCT Introduction and Resource
Guide" is available from the WWW server shown below (file
RESOURCE.PCT, 75 KB), or by mail (20 pages) as shown in the section
on references and order forms. It features the book jacket for
_Behavior: The Control of Perception_; two short essays by Bill
Powers: _An essay on the obvious_ and _Things I'd like to say if
they wouldn't think I am a nut_, which deal with the requirements
for and consequences of applying physical science to the field of
psychology; the foreword for _Living Control Systems II_ by Tom
Bourbon and more; plus more detailed descriptions of PCT books,
videos, order forms etc.

This introduction provides information about:

   Perceptual Control Theory (PCT): What it is
   Introductions to Perceptual Control Theory
   The Evolution of the Control Paradigm
   Demonstrating the Phenomenon of Control
   The Purpose of CSGnet
   CSGnet Participants
   Asking Questions
   Post Format
   The Control Systems Group
   Accessing and Subscribing to CSGnet
   Gopher and World-Wide Web
   On-line documents
   Order Forms


PCT offers a clear explanation for the pervasive phenomenon of
control, which is also known as purposeful behavior. Hierarchical
PCT (HPCT) outlines a hierarchical arrangement as a likely
organization of multiple control systems, which can explain the
purposeful behavior of living organisms.

PCT and HPCT were developed by William T. Powers, and introduced in
his 1973 book _Behavior: The Control of Perception_. (See
references and order forms, below). Powers shows us that the
engineering concept of control helps improve our understanding of
behavior, conflict, cooperation, and personal relationships. Just
as the in-depth explanatory theories of modern physical science
have helped us understand inanimate objects better than was
possible with experience and descriptive theories alone, the
in-depth explanations of PCT help us understand living organisms
better than has been possible with experience and descriptive

PCT focuses on how we look at and experience things, and the way
these perceptions are compared with experiences we want. The
difference produces action and physiology. Thus PCT explains how
thoughts become actions, feelings and results, and its principles
can be applied to any activity involving human experience.

PCT helps us understand people as they naturally are, just as
engineers understand physical phenomena as they naturally are. PCT
is remarkably simple, but like any other applied science, it
requires an understanding of basic principles and practice in their

Much of the discussion on CSGnet reflects the rigorous "engineering
science" discipline of PCT and HPCT. Those who apply PCT and HPCT
to issues of personal relationships, education and management are
applying the basic principles to areas where they have not yet been
proven with scientific rigor, but seem to work well indeed.


Here are introductions by Bill and Mary Powers:

                 * * * * * * * *

  There have been two paradigms in the behavioral sciences since
  the 1600's. One was the idea that events impinging on organisms
  make them behave as they do. The other, which was developed in
  the 1930's, is PERCEPTUAL CONTROL THEORY (PCT). Perceptual
  Control Theory explains how organisms control what happens to
  them. This means all organisms from the amoeba to humankind. It
  explains why one organism can't control another without physical
  violence. It explains why people deprived of any major part of
  their ability to control soon become dysfunctional, lose interest
  in life, pine away and die. It explains what a goal is, how goals
  relate to action, how action affects perceptions and how
  perceptions define the reality in which we live and move and have
  our being. Perceptual Control Theory is the first scientific
  theory that can handle all these phenomena within a single,
  testable concept of how living systems work.

           William T. Powers, November 3, 1991

                 * * * * * * * *

  While the existence of control mechanisms and processes (such as
  feedback) in living systems is generally recognized, the
  implications of control organization go far beyond what is
  generally accepted. We believe that a fundamental characteristic
  of organisms is their ability to control; that they are, in fact,
  living control systems. To distinguish this approach from others
  using some version of control theory but forcing it to fit
  conventional approaches, we call ours Perceptual Control Theory,
  or PCT.

  PCT requires a major shift in thinking from the traditional
  approach: that what is controlled is not behavior, but
  perception. Modelling behavior as a dependent variable, as a
  response to stimuli, provides no explanation for the phenomenon
  of achieving consistent ends through varying means, and requires
  an extensive use of statistics to achieve modest (to the point of
  meaningless) correlations. Attempts to model behavior as planned
  and computed output can be demonstrated to require levels of
  precise calculation that are unobtainable in a physical system,
  and impossible in a real environment that is changing from one
  moment to the next. The PCT model views behavior as the means by
  which a perceived state of affairs is brought to and maintained
  at a reference state. This approach provides a physically
  plausible explanation for the consistency of outcomes and the
  variability of means.

  The PCT model has been used to simulate phenomena as diverse as
  bacterial chemotaxis, tracking a target, and behavior in crowds.
  In its elaborated form, a hierarchy of perceptual control systems
  (HPCT), it has lent itself to a computer simulation of tracking,
  including learning to track, and to new approaches to education,
  management, and psychotherapy.

  Control systems are not new in the life sciences. However,
  numerous misapprehensions exist, passed down from what was
  learned about control theory by non-engineers 40 or 50 years ago
  without further reference to newer developments or correction of
  initial misunderstandings. References in the literature to the
  desirability of positive feedback and the assertion that systems
  with feedback are slower than S-R systems are simply false, and
  concerns about stability are unfounded.

  The primary barrier to the adoption of PCT concepts is the
  belief--or hope--that control theory can simply be absorbed into
  the mainstream life sciences without disturbing the status quo.
  It is very hard to believe that one's training and life work, and
  that of one's mentors, and their mentors, must be fundamentally
  revised. Therefore, PCT appeals to those who feel some
  dissatisfaction with the status quo, or who are attracted to the
  idea of a generative model with broad application throughout the
  life sciences (plus AI and robotics). There are very few people
  working in PCT research. Much of its promise is still simply
  promise, and it meets resistance from all sides. It is
  frustrating but also tremendously exciting to be a part of the
  group who believe that they are participating in the birth of a
  true science of life.

           Mary Powers, November 1992

                 * * * * * * * *


The PCT paradigm originates in 1927, when an engineer named Harold
Black completed the technical analysis of closed loop control
systems. He was working with the negative feedback amplifier, which
is a control device. This led to a new engineering discipline and
the development of many purposeful machines. Purposeful machines
have built-in intent to achieve specified ends by variable means
under changing conditions.

The explanation for the phenomenon of control is the first
alternative to the linear cause-effect perspective ever proposed in
any science.

The first discussion of purposeful machines and people came in 1943
in a paper called: Behavior, Purpose and Teleology by Rosenblueth,
Wiener and Bigelow. This paper also argued that purpose belongs in
science as a real phenomenon in the present. Purpose does not mean
that somehow the future influences the present.

William T. (Bill) Powers developed PCT, beginning in the mid-50's.
In 1973 his book called "Behavior: the Control of Perception."
(often referred to as B:CP) was published. It is still the major
reference for PCT and discussion on CSGnet.

B:CP spells out a suggestion for a working model of how the human
brain and nervous system works. Our brain is a system that controls
its own perceptions. This view suggests explanations for many
previously mysterious aspects of how people interact with their

Perceptual Control Theory has been accepted by independently
thinking psychologists, scientists, engineers and others. The
result is that an association has been formed (the Control System
Group), several books published, this CSGnet set up and that
several professors teach PCT in American universities today.


Few scientists recognize or understand the phenomenon of control.
It is not well understood in important aspects even by many control
engineers. Yet the phenomenon of control, when it is recognized and
understood, provides a powerful enhancement to scientific

It is essential to recognize that control exists and deserves an
explanation before any of the discourse on CSGnet will make sense.

Please download the introductory computer demonstrations,
simulations and tutorials, beginning with "demo1". See "Gopher and
World-Wide Web" below for obtaining files via FTP, Gopher, and WWW.


CSGnet provides a forum for development, use and testing of PCT.


Many interests and backgrounds are represented here. Psychology,
Sociology, Linguistics, Artificial Intelligence, Robotics, Social
Work, Neurology, Modeling and Testing. All are represented and
discussed. As of March 20, 1995 there were 146 individuals from 20
countries subscribed to CSGnet.


Please introduce yourself with a statement of your professional
interests and background. It will help someone answer if you spell
out which demonstrations, introductory papers and references you
have taken the time to digest.


When you are ready to introduce yourself and post to CSGnet, please
begin each post with your name and date of posting at the beginning
of the message itself, as shown here:

[From Dag Forssell (960212 1600)]

This lets readers know who sent the message, and when (sometimes
very different from the automated datestamp). It provides a
convenient reference for replies. When you respond to a message,
please use this reference (remove the word "From"), and quote only
relevant parts of the message you comment on.


The CSG is an organization of people in the behavioral, social, and
life sciences who see the potential in PCT for increased
understanding in their own fields and for the unification of
diverse and fragmented specialties.

Annual dues are $20 for full members and $5 for students.

The Twelfth North American Annual Meeting of the CSG will held in
1996 from July 17 to 21 at Northern Arizona University in
Flagstaff, Arizona. Shuttle service from the Phoenix airport to
Flagstaff will be available. There will be seven plenary meetings
(mornings and evenings), with afternoons, mealtimes, and late night
free for further discussion or recreation. Full details will be
available on CSGnet or by mail after April 1, 1996. The Second
Meeting of the European Control Systems Group (ECSG) will also be
held in 1996. Details to be arranged and posted on this net.

For membership information write:
CSG, c/o Mary Powers, 73 Ridge Place CR 510, Durango, CO 81301-8136
USA or send e-mail to


CSGnet can also be accessed via Usenet where it is listed as the
newsgroup "bit.sci.purposive-behavior" (NOTE: You may have to set
your default news server to to read this group.)

To subscribe to the listserv version of CSGnet, and learn about
options & commands, subscribers and archives, send a message to


Message: (Comments: Not part of your message)

Subscribe CSGnet Firstname Lastname Institution (Your OWN name)
help (Basic introduction to commands)
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query CSGnet (Your mail status & options)
review CSGnet countries (Subscribers & addresses, by country)
index CSGnet (List of archive files available to you)
get CSGnet LOG9602B (Get archive for second week of Feb 1996
                           --shown here as an example only).

* The alternatives are:
set CSGnet mail (Get messages as they are posted)
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The Bitnet address for the list server is listserv@uiucvmd.

To remove yourself from the listserv version of CSGnet, send a

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For the "unsub" command to work, the command must be sent with the
same return address used for the original "subscribe" command.

Messages to the entire CSGnet community should be addressed to

For more information about accessing CSGnet, contact Gary Cziko,
the network manager, at


A number of documents as well as MS-DOS and Mackintosh computer
programs can be obtained via Gopher and the World-Wide Web
(currently under construction).

To use a Gopher browser, connect to and follow
the path:

Higher Education Resources/
Professional societies & journals/
Control Systems Group

or from your favorite Gopher server follow the path:

Other Gopher and Information Servers/
North America/
University of Ill.--College of Education/
Higher Education Resources/
Professional societies & journals/
Control Systems Group

The WWW address for the CSG homepage (under construction) is (don't forget the final slash).


A large collection of extracts from CSGnet discussions can be found
at on the World Wide Web at In addition,
extracts from selected published works can be found among the
references list below.


Here are some selected books, papers and computer programs on
Perceptual Control Theory. For a very complete list of CSG-related
publications, get the file biblio.pct from the fileserver as
described above. See also the "PCT Introduction and Resource Guide"
and order forms below.

                 * * * * * * * *

Bourbon, WT, KE Copeland, VR Dyer, WK Harman & BL Mosely (1990). On
the accuracy and reliability of predictions by control-system
theory. Perceptual and Motor Skills, vol 71, 1990, 1331-1338.
  The first of a 20-year series demonstrating the long-term
  reliability and stability of predictions generated by the PCT

Bourbon, W. Tom (In Press). Perceptual Control Theory. In: HL
Roitblat & J-A Meyer (eds.). Comparative approaches to cognitive
science. Cambridge, MA: MIT Press.
  Chapter surveys applications of PCT modeling by Bill Powers and
  Greg Williams (pointing, from the ARM/LITTLE MAN program); by
  Rick Marken and Bill Powers (movement "up a gradient" by E.
  coli), by Bill Powers, Clark Mcphail and Chuck Tucker (social
  movement and static formations, from the GATHERINGS program), and
  by Bourbon (tracking). The PCT model is contrasted with some of
  the mainstream models and theories presented at the workshop.

Cziko, Gary A. (1992). Purposeful behavior as the control of
perception: Implications for educational research. Educational
Researcher, 21(9), 10-18, 27.
  Introduction to PCT and implications for educational research.

Cziko, Gary A. (1992). Perceptual control theory: One threat to
educational research not (yet?) faced by Amundson, Serlin, and
Lehrer. Educational Researcher, 21(9), 25-27.
  Response to critics of previous article.

Cziko, Gary. (1995). Without miracles: Universal selection theory
and the second Darwinian evolution. Cambridge: MIT Press/A Bradford
     See Chapter 8, "Adapted Behavior as the Control of Perception"

Ford, Edward E. (1989). Freedom From Stress. Scottsdale AZ: Brandt
Publishing. A self-help book.
  PCT in a counseling framework.

Ford, Edward E. (1987). Love Guaranteed; A Better Marriage In 8
Weeks. Scottsdale AZ: Brandt Publishing.

Ford, Edward E. (1994). Discipline for Home and School. Scottsdale
AZ: Brandt Publishing.
  Teaches school personnel and parents how to deal effectively with

Forssell, Dag C., (1993). Perceptual Control: A New Management
Insight. In Engineering Management Journal, 5(4), 17-25.

Forssell, Dag C., (1994). Perceptual Control: Management Insight
for Problem Solving. In Engineering Management Journal, 6(3),

Forssell, Dag C., (1995). Perceptual Control: Leading
Uncontrollable People. In Engineering Management Journal, 7(1), 38-

Forssell, Dag C., (1994). Management and Leadership: Insight for
Effective Practice.
  A collection of articles (shown above) and working papers in book
  form introducing and applying PCT in the context of business and

Forssell, Dag C. (Ed.), (1995). PCTdemos and PCTtexts. Two DOS
disks 1.44 MB 3 1/2". May be freely copied. Also available at the
WWW site shown above.
  PCTdemos holds eight different tutorial, simulation and
  demonstration programs with documentation. PCTtexts holds 3+ MB
  of essays, explanation, and debate.

Gibbons, Hugh. (1990). The Death of Jeffrey Stapleton: Exploring
the Way Lawyers Think. Concord, NH: Franklin Pierce Law Center.
  A text for law students using control theory.

Hershberger, Wayne. (Ed.). (1989). Volitional Action: Conation and
Control (Advances in Psychology No. 62). NY: North-Holland.
  16 of 25 articles on or about PCT.

Judd, Joel. (1992). Second Language Acquisition as the Control of
Nonprimary Linguistic Perception: A Critique of Research and
Theory. Unpublished doctoral dissertation, University of Illinois
at Champaign-Urbana. Dissertation Abstracts International, 53, (7),

Marken, Richard S. (Ed.). (1990). Purposeful Behavior: The control
theory approach. American Behavioral Scientist, 34(1). (Thousand
Oaks, CA: Sage Publications).
  11 articles on control theory.

Marken, Richard S. (1992). Mind Readings: Experimental Studies of
Purpose. NC: New View.
  Research papers exploring control.

McClelland, Kent. 1994. Perceptual Control and Social Power.
Sociological Perspectives 37(4):461-496.

McClelland, Kent. On Cooperatively Controlled Perceptions and
Social order. Available from the author, Dept. of Sociology,
Grinnell College, Grinnell IOWA 50112 USA.

McPhail, Clark. (1990). The Myth of the Madding Crowd. New York:
Aldine de Gruyter.
  Introduces control theory to explain group behavior.

McPhail, Clark., Powers, William T., & Tucker, Charles W. (1992).
Simulating individual and collective action In temporary
gatherings. Social Science Computer Review, 10(1), 1-28.
  Computer simulation of control systems in groups.

Petrie, Hugh G. (1981). The Dilemma of Inquiry and Learning.
Chicago: University of Chicago Press.

Powers, William T. (1973). Behavior: The Control of Perception.
Hawthorne, NY: Aldine DeGruyter.
  The basic text.

Powers, William T., The Nature of Robots:
  1 Defining Behavior BYTE 4(6), June 1979, p132-144, 7 pages.
  2 Simulated Control System, BYTE 4(7), July, 134-152, 12p.
  3 A Closer Look at Human Behavior, BYTE 4(8), Aug, 94-116, 16p.
  4 Looking for Controlled Variables, BYTE 4(8), Sep 96-112, 13p.

Powers, William T. (1989). Living Control Systems: Selected Papers.
NC: New View.
  Previously published papers, 1960-1988.

Powers, William T. (1992). Living Control Systems II: Selected
Papers. NC: New View.
  Previously unpublished papers, 1959-1990

Richardson, George P. (1991). Feedback Thought in Social Science
and Systems Theory. Philadelphia: University of Pennsylvania Press.
  A review of systems thinking, including PCT.

Robertson, Richard J. and Powers, William T. (Eds.). (1990).
Introduction to Modern Psychology: The Control Theory View. NC: New
  College-level text.

Runkel, Philip J. (1990). Casting Nets and Testing Specimens. New
York: Praeger.
  When statistics are appropriate; when models are required.

                 * * * * * * * *


  A free 20 page PCT Resource Guide with introductions and more
  detail on the references listed above and a few more --
  publishers, books, articles, videos, seminars, and the DOS
  demonstration disk -- may be obtained by sending a note to:

           PCT Introduction and Resource Guide
           Dag Forssell
           23903 Via Flamenco
           Valencia, California, 91355-2808 USA.

The PCT Introduction and Resource Guide is also available in ASCII
format from the WWW site shown above.

Order forms in the Guide are reproduced below without descriptions.
All prices current as of April, 1995.


Purposeful Leadership: Dag Forssell Telephone: (805) 254-1195
23903 Via Flamenco, Valencia, CA 91355-2808 USA Fax:(805) 254-7956

___ ea Management and Leadership: Insight for ... @ $20.00 ______
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___ ea Rubber Band Demo. Video & Script 63 minutes @ $20.00 ______
___ ea PCT supports TQM. Video 117 minutes @ $20.00 ______
___ ea PCT @ AERA 1995. Video 120 minutes @ $10.00 ______
___ ea 1993 CSG conference. 3 videos, 18 hours. @ $30.00 ______
___ ea 1994 CSG conference. 3 videos, 16 hours. @ $30.00 ______
___ ea Freedom From Stress. Book by Ed Ford @ $10.00 ______
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___ ea LIVING CONTROL SYSTEMS @ $16.50 _______
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  American Behavioral Scientist, Volume 34, Number 1 Sept/Oct 1990
       Stock number 201238 Richard S. Marken, Editor
       Purposeful Behavior; The Control Theory Approach,
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