Disruptive Design
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Disruptive Design

Tools for Systems Thinkers: Getting into Systems Dynamics… and Bathtubs

In the last chapter of this series, The 6 Fundamental Concepts of Systems Thinking, I explored some of the key concepts of systems thinking such as interconnectedness, synthesis, emergence, causality and feedback loops. In this chapter, I will delve into what defines a system and move into more detail with stocks and flows in systems (which, for some reason, is often described using a bathtub analogy — something that I find very odd!).

Before I start let me clarify something. Systems thinking (like many fields), has varying opinions, theories, processes, techniques, methods and modes, emerging from different fields of thought and action. My objective in this series is to synthesize as much as I can into short, concise and accessible language that enables access to the complexity, so that more people can understand and design for systems change.

I love systems thinking — it’s one of the best tools we have to develop a more detailed, dynamic and divergent perspective of the way the world works. I hope that these words and insights from my years of working with and teaching systems, sustainability and design can help you develop a systems mindset as well.

What defines a system?

If you had to, what words would you use to define a system? Funnily enough, many important systems are easily identified by the word ‘system’ after them, such as respiratory, education, legal or mechanical systems. Systems are absolutely everywhere, of all manner, shapes, and size from the intricate workings of your body (nervous, neurological, digestive, cardiovascular etc), to the infinite possibility of space — our world is made up of interconnected and interdependent systems.

To define a system, it must be both dynamic (constantly changing) and evolving (having emergent properties). It must be connected to elements, actors, agencies, nodes, stocks or ‘parts,’ and have a boundary. The edge of the universe is perhaps one exception to this, but we can still define a solar system by the boundaries of a constellation.

One of my favorite systems thinkers is Draper Kauffman, who wrote this perfect ‘101 guide’ in the early 80’s (also up there in the favorites list are Ackoff, Meadows and Senge and Bertalanffy*1). In his paper, Kauffman uses an analogy to describe what defines a system with the help of a cow:

“…dividing the cow in half does not give you two smaller cows. You may end up with a lot of hamburger, but the essential nature of “cow” — a living system capable, among other things, of turning grass into milk — then would be lost. This is what we mean when we say a system functions as a “whole”. Its behavior depends on its entire structure and not just on adding up the behavior of its different pieces.” — Kauffman, 1980, p2

The cow itself is a system, defined by the system boundary of its skin, interconnected with the industrial (or natural) system of a farm that benefits from the ecosystem of nutrients and sun to grow grass, etc. But when the cow is cut up, for a brief moment it becomes a stagnant and disconnected heap. Under new conditions, it will enter into the industrial food production system, decompose into the natural system providing nutrients back to nature, or pass through a digestive system and contribute to that system’s own function.

Point being, systems are defined by their interrelationships and their functionality or potential.

In many cases when you take one part of the system away it ceases to function, such as taking the wheels off a car or removing a vital organ from a body. It’s the interconnectedness that makes a system work, and one of the best examples of interactive systems design is nature — it is composed of many individual parts working together to create the dynamic whole that is the planet.

The point that Kauffman makes is that systems have to be dynamic. When you disconnect a system, it becomes a lifeless heap. This can be applied to to human made systems, such as your cell phone. Without electricity, the primary function that motivated its creation is now removed and it becomes a functionless heap of metal, held together by glass (with the potential to feed a recycling system, but often ends up locked in people’s drawers). But once you plug it into the complexity of a constantly flowing electrical distribution system, power and functionality are reinstated.

Systems are made up of interconnected parts that when put together create a complex whole. Think about a jigsaw puzzle — the individual parts may or may not make immediate sense, but placed together, the entire whole is the obvious outcome of the parts.

How to think in systems

What makes system thinking applicable in real-world problem solving, without overwhelming the practitioner, is the power of defining a system boundary. Without a clear boundary, there are infinite interconnected possibilities, which often overwhelms new systems thinkers. It’s the vastness — the seemingly endless possibility — that often trips up newbies and can make some brains explode (I often hear in workshops: “But if everything is interconnected, then there is no beginning or end, and I am one tiny person in this big infinite system and ahhhhh!”).

Don’t worry; this is normal and I have some tricks that I have developed to help overcome this.

The reality is that everything is interconnected, but everything can also be defined by a function, purpose or potential in some way. A tree’s system boundary can be defined by its bark and its myriad of ecosystem services/functions: to produce oxygen and store water, it is dynamically connected to the ecosystem that it draws energy and nutrients from, and provides resources back into. Likewise, we are defined by our own skin. Inside our bodies, we are a complex array of systems that are all beautifully functioning to keep us alive. At the same time, are also connected to the same ecosystems that keep the tree alive.

I first encountered system boundaries when working in life cycle assessment, which has an international standard that demands the defining of a system boundary when comparing the environmental impacts of products or services. Starting to think this way allowed me to see the tiny parts that make up the obvious whole, and more importantly, how they connect together to make even bigger wholes. This is another core thinking tool of systems thinking — parts, wholes and relationships. So after years of seeing eyes widen and minds start to melt, I expanded the systems boundary concept to include some practical tools to help curious minds move through levels of systems thinking.

Systems Boundaries

The first thinking tool is the swimming pool and the ocean analogy. When you first learn to swim, starting off in a pool that has clearly defined edges to grip and a shallow end gives you the confidence to explore and learn. The ocean, on the other hand, can be overwhelming and perceived as dangerous. But just because you are swimming in a pool doesn’t mean you don’t know about the ocean; in fact, the ocean is often the end goal that you’re working toward. So, as you build your systems mindset, start with a defined system boundary: a pool where you can determine the edges and know what you are dealing with before you jump into the ocean. Trust me — as simplistic as this is, it will help build your systems thinker skills in the long run. Start small, and build to big.

Connected to this idea is the thinking-in-telescopes tool. A systems thinker can think at both the micro element scale that can be seen inside a microscope, as well as the macro infinite possibility scale that can be witnessed through a telescope — all while having a firm view of the landscape around them. Being able to move through these scales from the micro to the massive, allows for a shifting of perspectives to build a 3-dimensional worldview.

Next, we have the lensing tool, a name I gave to the approach that describes shifting perspectives in order to gain a ‘below the surface’ exploration. I like to think of it like as how lighting technicians can change a live theater show by changing the color filter of the white light; pop a red filter on, and it’s moody and dark, pop a blue one on, and it’s light and angelic. But instead of color filters, lensing is about shifting your perspective or trying on a different viewpoint to gain a divergent understanding of the world or the phenomena you are seeking to understand.

From this different point of view, we can build empathy (which is the visceral experience of being connected to the lived experience of another), as it allows us to step outside of the often restrictive thinking that our own minds like to impose on us for safety and security (more on this in a later chapter).

Understanding a System

Now that you have some of the basic applied systems tools in place, let’s jump to ways of understanding a system. First, you need to define the system boundary: what is it that you are exploring, and what are the boundaries of the system? The cool thing about defining this is that it is then super clear to everyone what you are, and are not, looking at. I use a simple piece of paper and write the problem arena or system element I want to explore smack bang in the middle (more on cluster mappings in the next chapter in this series).

Once you have started to map out and define your system arena, you then start to granulate. In the same way rocks break down over time into smaller and smaller parts to eventually become fine grains of sand, you move from the telescope to the microscope and start to really tease out all the finer details of the system. You may only select one part to do so, but it’s through granulation that you will start to dive under the surface and push your brain to seek out the non-obvious parts of the system.

From here, you are set to start to draw out some insights or questions that will feed you into a deeper cycle of inquiry. When applied in the Disruptive Design Method (MLB), this is where we cycle through a phase in the Mining, Landscaping & Building methodology more on the MLB approach here). But in any systems thinking scenario, you want to use the exploration as the feedstock for the next level of inquiry.

One of the key concepts here is the Iceberg Model and mental models, where although most thinking is done on the surface level, we must dive deeper under the surface to explore the majority of the mass. What is holding it up? After this, you are set to start to tease out what the feedbacks within the system are.

Stocks and Flows

But first, let’s get a little nerdy for a moment. Donella Meadows, a critical pioneer of systems thinking, authored Thinking in Systems, A Primer*(2), where she summarized her very detailed exploration of stocks and flows.

A stock is anything that exists within the system (like people, trees, money, cats, pineapples, students, guns, happiness, etc.), and flows are the feedbacks between these stocks (like how money moves through the economy or how water flows through a waterway) and the change in stocks over time. I could go further into this, but it does start to get into a whole different level of nerd (for a DIY version start here).

So much of the literature on this topic talks about bathtubs, an analogy that goes like this: Bathtub is a stock that water flows through. There is an inpipe (the tap) and an outflow (the plug). Water is a stock, and the flow is the rate at which it moves through the bath based on the variables of the plug and tap. You can measure the change over time based on the flow of water through the tub. I promise to never talk about bathtubs again*(3).

The reason we look at things moving through other things in systems dynamics is because we are using observation to understand the behavior of these things and how they impact those other things (causality). From there, the next step is to understand the feedbacks within the systems (more coming up in chapter 4 for this).

Systems dynamics is a huge field, and it can be overwhelming*(4)— but the main points to start off with are that systems are constantly changing. They can be defined by boundaries, but are dynamically interconnected and they can be explored through stocks and flows.

Next up in the series, I am going to share some techniques for analog systems mapping so you start applying this approach to problem solving in your professional practices. If you want a little exercise to start with, try identifying and scoping systems around you as you walk down the street, or sit in your next (boring?) meeting. You can level it up by thinking through the stocks and flows within the systems you identify.


  1. There are WAY more prominent past and current systems thinkers contributing to the field. The Systems Thinker website is a great resource for exploring the theories and theorists in more detail.
  2. I wish I could link to all the resources out there, but since that’s infinitely impossible, we started this visual collection over on Pinterest of some useful systems thinking resources.
  3. Emma Segal (who does all the lovely illustrations on this series) refused to draw me a bathtub to demonstrate this.
  4. Have fun! Systems thinking is a super enjoyable way of experiencing the magic of the world and if you want to go deeper check out my class on systems interventions here.
  5. Check out all the classes and workshops we have supporting adopting systems thinking and activating positive change




This curated collection of articles explores the themes of disruptive design, sustainability, cognitive science, systems thinking, social innovation, the circular economy and the systems that connect it all.

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Leyla Acaroglu

Leyla Acaroglu

UNEP Champion of the Earth, Designer, Sociologist, Sustainability Provocateur, TED Speaker, Educator, Founder of unschools.co, disrupdesign.co & coproject.co

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