1. THINKING IN SYSTEMS
CHAPTER 1: THE BASICS
DONELLA MEADOWS

2. WHAT IS A SYSTEM?
“A system is an interconnected set of elements
that is coherently organized in a way that
achieves something (function or purpose).”

3. WHAT MAKES A SLINKY BOUNCE
UP AND DOWN?
The answer clearly lies within
the Slinky itself.
The hands that manipulate it
suppress or release some
behavior that is latent within the
structure of the spring. That is a
central insight of systems
theory. Once we see the
relationship between structure
and behavior, we can begin to
understand how systems work.

4. THE BLIND MEN & THE ELEPHANT
The behavior of a system cannot be known just by
knowing the elements of which the system is made.

5. DIGESTIVE SYSTEM
TEETH
INTERCONNECTIONS
MOUTH • Physical flow of
food
• Regulating chemical
signals
STOMACH
ENZYMES
The function of the digestive system is to break down food into its
basic nutrients and to transfer those nutrients into the
bloodstream (another system) while discarding unusable wastes.

6. A FOOTBALL TEAM
COACH
PLAYERS Interconnections
• Rules of the game
• Coach’s strategy
• Player’s communications
• Laws of physics that
govern the motions of
balls & players
BALL FIELD
Purpose: Win games, have fun, make millions of dollars, or all of the above.

7. EXAMPLES OF SYSTEMS
School Factory Solar System
Tree Animal
Forest

8. CHARACTERISTICS OF A SYSTEM
• Integrity or wholeness
• Adaptive
• Resilient
• Evolutionary
• Goal-seeking
• Self-preserving
• Self-organizing

9. INTERCONNECTIONS
• The relationships that hold the elements
together
• Many of the interconnections in systems
operate through the flow of information.
Information holds systems together and
plays a great role in how they operate.

10. FUNCTION/PURPOSE
• Function is used for a nonhuman system,
and purpose for a human one. Many
systems have both human and non-human
elements
• Purposes are deduced from behavior, not
from rhetoric or stated goals

11. SYSTEMS WITHIN SYSTEMS
S
u Student
Purpose: To get good grades
b
-
s
y
University
Purpose: To discover & preserve knowledge s
t Professor
Purpose: To get tenure
e
• Keeping sub-purposes and m
overall system purposes in s
harmony is an essential
function of successful
systems.
Administrator
Purpose: To balance the budget

12. IMPACT ON SYSTEM WHEN
CHANGES ARE MADE
The elements are the parts of the system we
are most likely to notice. They are least
important in defining the unique characteristics
of the system. Changing elements has the least
effect n the system
If interconnections change, the
system may be greatly altered.
Function/purpose is the least obvious part
of the system. It is the most crucial
determinant of the system’s behavior.
Changes in function or purpose can be
drastic / profound

13. STOCKS & FLOWS
Ba th tub
The water in a bathtub is stock
Flows are filling and draining the bathtub
• A Stock is the foundation of any system. Stocks are the elements of the
system that you can see, feel, count, or measure at any given time.
• Stock change over time through the actions of the flow.

14. STOCKS & FLOWS
Bat ht ub
ad ding wat er draining wa te r
The faucet and the drain are flows

15. STOCKS & FLOWS
Stock
Inflow Outflow
1. Stocks are shown as boxes
2. The flows are arrow-headed pipes, leading into or out of the stocks.
3. The small T on each flow signifies a faucet.
4. The clouds stand for wherever the flows come from and go to (i.e. the sources and the
sinks).

16. BEHAVIOR OVER TIME GRAPHS
Draining
Water level in tub when the plug is pulled
1: Bathtub
1: 30
1
1
1: 15
1
1
1: 0
0.00 7.50 15.00 22.50 30.00
Minutes 11:46 AM Fri, Feb 20, 2009
Water in bathtub
• System thinkers use graphs of system behavior to understand trends over time,
rather than focusing attention on individual events
• Behavior-over-time graph is used to learn whether the system is approaching a
goal or limit, and if so, how quickly.

17. UNDERSTANDING
BEHAVIOR OVER TIME
Dynamic Equilibrium
1: Bathtub
1: 26
1: 25 1 1 1 1
1: 24
0.00 7.50 15.00 22.50 30.00
Minutes 11:34 AM Fri, Feb 20, 2009
Water in bathtub
Principles
• If the sum of all outflows equals the sum of all inflows, the stock level will not
change; it will be held in dynamic equilibrium
• As long as the sum of inflows exceeds the sum of all outflows, the level of stock
will rise
• As long as the sum of all outflows exceeds the sum of all inflows, the level of
stock will fall

18. THE ROLE OF STOCKS IN
SYSTEMS
• A Stock takes time to change, because
flows take time to flow.
• Changes in stocks set the pace of the
dynamics of systems.
• Most individual and institutional
decisions are designed to regulate
levels of stock
• System thinkers see the world as a
collection of stocks along with the
mechanisms for regulating levels in the
stocks by manipulating flows.

19. OTHER STOCKS &
FLOWS
Ban k Acc ount
C02 I n
At mosp here
mak in g d epo sits
ad ding c0 2
Se lf E ste em
bu ildin g
Same thing, different units

20. FEEDBACK LOOPS
A feedback loop occurs when a stock affects its flows
Ban k acc oun t
ea rn in g in teres t
int erest rat e R
• A Feedback loop is formed when changes in stock affect the flows into or out of that same stock.
Example: Total amount of money in an account (stock) affects how much money comes into the
account as interest.
• Feedback loops can cause stocks to maintain their level within a range or grow or decline. The
stock level feeds back through a chain of signals and actions to control itself.

21. FEEDBACK LOOPS
1. STABILIZING LOOPS - BALANCING FEEDBACK
Energy Level of a Coffee Drinker
The feedback loop can
correct an oversupply or an
undersupply
• This kind of feedback loop stabilizes the stock level. It is stabilizing, goal
seeking, regulating and is called a Balancing Feedback Loop.
• The stock level may not remain completely fixed, but it does stay within an
acceptable range.

22. HOMING BEHAVIOR OF THE
BALANCING FEEDBACK LOOP
Whatever the initial value of the system
stock (coffee temperature in this case),
whether it is above or below the “goal”
(room temperature), the feedback loop
brings it toward the goal. The change is
faster at first, and then slower, as the
discrepancy between the stock and the
goal decreases.

23. FEEDBACK LOOPS
2. RUNAWAY LOOPS - REINFORCING FEEDBACK
Population
Bank acc ount births
earning interest
R R
birth rate
interest rate
Reinforcing loops are found wherever a system element has the ability
to reproduce itself or to grow as a constant fraction of itself. Those
elements include populations and economies.

24. THINKING IN SYSTEMS
CHAPTER 2: A BRIEF VISIT TO THE SYSTEMS ZOO
DONELLA MEADOWS

25. ONE-STOCK SYSTEMS
A Stock with Two Competing Balancing Loops

26. ONE-STOCK SYSTEMS
A Stock with One Reinforcing Loop and One
Balancing Loop—Population and Industrial Economy
SHIFTING DOMINANCE OF FEEDBACK LOOPS: When one loop
dominates another, it has a stronger impact on behavior. Because systems
often have several competing feedback loops operating simultaneously,
those loops that dominate the system will determine the behavior.

27. ONE-STOCK SYSTEMS
A Stock with One Reinforcing Loop and One
Balancing Loop—Population and Industrial Economy
Systems with similar feedback structures produce similar dynamic
behaviors, even if the outward appearance of these systems is completely
dissimilar.

28. ONE-STOCK SYSTEMS
A System with Delays—Business Inventory
Delays are pervasive in systems, and they are strong determinants of
behavior. Changing the length of a delay may (or may not, depending on the
type of delay and the relative lengths of other delays) make a large change
in the behavior of a system.

29. TWO-STOCK SYSTEMS
A Renewable Stock Constrained by a Nonrenewable
Stock — an Oil Economy
Nonrenewable resources are
stock-limited. The entire stock
is available at once, and can
be extracted at any rate
(limited mainly by extraction
capital). But since the stock is
not renewed - the faster the
extraction rate, the shorter the
lifetime of the resource.

30. TWO-STOCK SYSTEMS
Renewable Stock Constrained by a Renewable
Stock— a Fishing Economy
Renewable resources are
flow-limited. They can support
extraction or harvest
indefinitely, but only at a finite
flow rate equal to their
regeneration rate. If they are
extracted faster than they
regenerate, they may
eventually be driven below a
critical threshold and become,
for all practical purposes,
nonrenewable.

31. SYSTEMS SURPRISE US BECAUSE…
1. We pay too little attention to history. We are too fascinated by the
events they generate (pp.90)
2. We are not too skilled in understanding the nature of relationships
(pp.91) as the world is full of nonlinearities.
3. Beware of clouds! They are prime sources of system surprises.
4. We get attached to the boundaries our minds happen to be
accustomed to – often these boundaries are too large or too narrow
(pp.98)
5. Our minds like to think of single causes neatly producing single effects
6. We don’t recognize which factor is limiting. Growth depletes or
enhances limits and therefore changes what is limiting. (pp. 102)
7. We rarely see the full range of possibilities before us (pp. 106). We are
subject to bounded rationality i.e. we make reasonable decisions based
on the information we have.