Some commonly encountered stocks and flows
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INFLOWS
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STOCKS
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OUTFLOWS
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births
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Population
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deaths
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Inflows
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Stocks
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outflows
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increase
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Self-esteem
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decrease
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production
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Inventory
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shipments
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build-up
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Charge
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decay
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bookings
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Order
backlog
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sales
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construction
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Buildings
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demolition
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learning
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Knowledge
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forgetting
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Stocks and flows are the nouns and verbs
of the systems language. Stocks are the
"things" in the language. Flows are the "actions."
Stocks represent accumulations, and accumulations
are everywhere! The food in
your stomach. The money in your wallet. The knowledge in your head. The love in
your heart. They are accumulations and have surged and slumped, waxed and
waned, as life progresses.
At any point in time, the accumulations
of stocks in a system indicate how things
are going- whether the system is your body, your family, a corporation, a city, or an
ecosystem. If your stomach is too full, you're not comfortable. If your fuel gauge is
near Empty, you get worried. On the other hand, if you've just blown off some steam
by telling your overbearing boss what you really think of her, your chest probably
feels a lot lighter. As these examples illustrate, we assess the state of "things" by
assessing the magnitudes of the associated accumulations. Accumulations thus
serve as barometers. Their magnitudes tell us how things are going.
Why do the magnitudes of accumulations
matter to us?
Why have accumulations come to play the
role of reporters" of the state of a
system?
The reason is that accumulations both
enable and inhibit actions. They serve both
as resources and constraints. Nothing can happen without accumulations, both
physical and non-physical. Resources, residing in accumulations, enable all human
actions!
In their role as supporters of activity,
some resources are "consumable" while
others act as "catalysts."
Human energy reserves are a "consumable"
resource. Money and water are other
familiar consumable resources.
A stock of knowledge is required for actions.
Unlike energy reserves, knowledge is
not consumed in the process of taking action. It enables the activity to occur, but is
not consumed in the process. Therefore, resources such as knowledge are stocks
of catalysts. Love, self-confidence, and commitment are other catalytic resources.
Each may inspire action, but none is consumed in the subsequent process of
taking that action.
