As you will see, this Substack is full of diagrams comprising little clusters of words connected by arrows. These are called causal loop diagrams, or CLDs for short.
We make abundant use of CLDs because they make the flow of influences more obvious, in particular the circular nature of feedback loop flows. Feedback loops can be expressed in spoken or written sentences, but language is inherently linear, ill-suited to convey the essential loopiness of our subject matter.
Also, causal loop diagrams make it easier to grasp the relationship between the parts of the feedback loop and the loop taken as a whole. The parts of a feedback loop are the entities that act and are acted upon (shown as nodes on the CLD) and the relationships between the entities (shown as arrows). These entities and relationships combine to form a whole that is different from any of the parts. The whole can be an actor in its own right, influencing the larger system within which it is embedded. In the CLD, you can see all the parts and how they fit together. In the CLD, the loop appears as a coherent whole, just as an architectural drawing shows the building as a coherent whole along with its constituent parts.
An important caveat to keep in mind is that causal loop diagrams are models. They represent the CLD maker's understanding of some aspect of how the real world works, or should work, or did work at some time in the past, or will work in the future under some set of hypothesized conditions. The aphorism "All models are wrong, but some are useful" absolutely applies to CLDs. They cannot depict the workings of the real world in all of its glorious complexity, with its myriad of intertwined causal relationships. But they can be extremely useful to depict enough of the workings of a system to allow deeper thinking or clearer communication.
Most of CLDs in this substack depict Kim's and Tim's understanding of relationships that we think exist in the real world and have strong explanatory or predictive power about phenomenon that are important to humans. Occasionally we will draw a CLD to depict what we think someone else's mental model is, perhaps to point out where our mental model differs from theirs.
Here is some guidance on how to make sense of the causal loop diagrams in this substack:
• The clusters of words are called "nodes." Nodes depict entities in the real or imagined world that can change. The entities depicted by a CLD node should be able to increase and/or decrease in abundance, size, strength, prominence, frequency, velocity, effectiveness or other important attribute. If you like math, you can think of nodes as variables. In this Substack, italic font in a sentence usually refers to a node in a nearby CLD.
• An arrow means that there is a causal relationship or "link" between the nodes at the two ends of that arrow. If there is a change in the node at the upstream end of the node, that will cause or tend to cause a change in the downstream node.
• If there is an "S" on an arrow, that means that the two nodes connected by the arrow will tend to change in the samedirection. To take an example from the predator/prey CLD above, if Nourishment available for Predators goes up, then Population of predators will also tend to go up. If Nourishment available for Predators goes down, Population of predatorswill also tend to go down.
• If there is an "O" on an arrow, that means that the two nodes will tend to change in opposite directions. To continue with the predator/prey example, if the Chance of being eaten by a predator goes up (because Population of predators has gone up), the Population of prey will tend to go down. Conversely, if Chance of being eaten by predators goes down, the Population of prey will tend to go up, as they multiply in the absence of so much risk of predation. When one goes up, the other tends to go down, and vice versa.
• If there is an "R" in the middle of a CLD, that indicates that the person who made the causal model thinks that the situation is a Reinforcing feedback loop, in other words a system in which any nudge to a node of the system will result in a chain of influences that has the net effect of pushing the system farther and farther away from its position at the time of the nudge. (If this explanation is too minimalist, go to What are feedback loops?) Some CLD-makers put a "+" (for "positive") in the center of their CLDs in places where this substack uses an "R."
• If there is a "B" in the middle of the loop, that indicates that the person who made the causal model thinks that the situation is a Balancing feedback loop, in other words a system in which a nudge to the system results in a chain of influences that pulls the system back towards its position at the time of the initial nudge or towards a goal state or equilibrium state. (If this explanation is too minimalist, go to What are feedback loops?) Some CLD-makers put a "-" (for "negative") in the center of their CLDs in places where this substack uses an "B."
• Some of the CLDs in this substack have a large arrow beneath them labelled "Net effect." We use this convention to call attention to the effect of the feedback loop – taken in its entirety – on the larger system within which it is embedded. You can also think of this as the outcome of multiple circuits around the loop. For engineered or evolved systems, this is sometimes called the "function" of the system – what the feedback loop is accomplishing on behalf of the machine or organism.
• Some of the CLDs in this substack have a cloud symbol. We use this convention to indicate a potential intervention, a purposeful effort to change a feedback loop. In the CLD below, for pandemic spread, Vaccinations are an intervention to disrupt the link from Number of people who have inhaled the virus to Number of sick people. Masking & social distancing are interventions to disrupt the link from Number of sick people to Number of people who have inhaled the virus.
There is another type of diagram in common use in system dynamics, called a stock and flow diagram. If you aspire to make computational systems models, you will definitely need to learn to make such diagrams eventually. But for the immediate purpose of using your own brain to think more powerfully and communicate more clearly about feedback loops that matter in your personal or professional life, causal loop diagrams should work very well.