Simple vs. Complicated vs. Complex vs. Chaotic

When you’re managing software development projects, you need to know the difference between complex and complicated. Not knowing this difference means you might apply exactly the wrong approach to the right problem. (Or, if you prefer, the right approach to the wrong problem.)

It’s a simple message, really. But if you don’t get it, you’re headed for chaos.

Simple = easily knowable.

Complicated = not simple, but still knowable.

Complex = not fully knowable, but reasonably predictable.

Chaotic = neither knowable nor predictable.

My car key is simple.
It took me about three seconds to understand how my car key works. OK, maybe that’s not quite correct. Mine has a battery in it. If I take it apart it might take me another three hours to understand its details. But yeah, I’m smart, I’ll manage.

My car is complicated.
It would take me years to understand how my car works. And I don’t intend to. But if I did, then some day in the far future I would know with certainty the purpose of each mechanism and each electrical circuit. I would fully understand how to control it, and I would be able to take my car apart and reassemble it, driving it exactly as I did before. In theory, of course. In practice, only real men do things like that.

Car traffic is complex.
I can travel up and down the same street for twenty years, and things would be different every time. There is no way to fully understand and know what happens around me on the road when I drive, how other drivers operate their vehicles, and how the people in the streets interact. I can make guesses, and I can gain experience in predicting outcomes. But I will never know for sure.

Car traffic in Lagos (Nigeria) is chaotic.
When things get too complex, they easily become chaotic. Traffic in Lagos is so bad, it is not even predictable. Poor infrastructure and planning, heaps of waste, pollution, lack of security, floods, and many more problems make it one of the worst places in the world to be, as a simple car driver.

My computer is complicated. My software project is complex. My house is complicated. My household is complex. My blog is complicated. My thoughts are complex. Your dinner is complicated. Your dog is complex.

Simple and complicated systems are all fully predictable.

The main difference between predictable systems and complex systems is our approach to understanding them. We can understand simple and complicated systems by taking them apart and analyzing the details. However, we cannot understand complex systems by applying the same strategy of reductionism. But we can achieve some understanding by watching and studying how the whole system operates.

What’s important for managers is that this also works the other way around. We create complicated systems by first designing the parts, and then putting them together. This works well for mechanical things, like buildings, watches and Quattro Stagioni pizzas. But it doesn’t work for complex systems, like brains, software development teams, and the local pizzeria. We cannot build a system from scratch and expect it to become complex in the way that we intended. Complex systems defy attempts to be created in an engineering effort.

Complex systems are not constructed, they are grown.

Some people picture complexity as a state that somehow surpasses that of complicatedness (see next picture). But this view is incorrect.


From: Managing Game Design Risk: Part I

“Complicated” refers to a system having many parts, making it somewhat harder to understand, whereas “complex” refers to a system being not fully predictable. What is complicated is not necessarily complex, like two cars in a garage. And what is complex need not be complicated, like two people in a bedroom. (But what these people do in the bedroom can be quite complicated. And unpredictable.)


The correct picture might be something like the one above. In one dimension systems are either simple or complicated. This depends on the number (and type) of parts, and our own ability to comprehend them. There’s a fuzzy line between the two, as some people (our partners in particular) have more trouble than others at understanding even the simplest things.

Then there’s a second dimension in which systems are either predictable, complex or chaotic. You can see that we may apply the same distinction (simple vs. complicated) to both complex and chaotic systems, since some of these have parts that are either easy to comprehend (e.g. water molecules) or easy to count (e.g. pieces in a game of chess). But most complex systems are not easy to understand, which is why people often assume that every complex system is complicated as well. Software projects, whether simple or complicated, are always in the middle tier: they are complex.

When you manage a system, you need to know whether it is either predictable or complex. If you take the wrong approach to building or managing such a system, you’re either blow-drying your pizza, or microwaving your dog. And chaos might unfold.

Simple, isn’t it?

Complicated and Complex (Flemming Funch)
Software: Complex vs. Complicated (Pierre de Vries)
More on Complex versus Complicated (Robert Paterson)
Scrum and Complexity (Stacia Broderick)
Is your city too chaotic? (BBC News)

Note: This post is published automatically while I’m swimming in a pool in Cuba. I will respond to any replies and comments, but it might take a while.

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  • Sonja

    A very simple explanation on the distinction between complex and complicated, described by Langtons Ant.
    An ant lives in a world like an infinite chessboard, filled with all squares. All the squares start out white. When the ant walks over a square the square changes color (only black and white). The ant follows two simple (not complicated) rules:
    1. If he steps on a white square he’ll turn left.
    2. If he steps on a black square he’ll turn right.
    This is something which is very easy to imagine. After (quite) some time the ant will be walking in the same circle continuously. Now try and figure out, without going through the steps what his path will be like.
    Scientist have not been able to figure this out yet. In a complex world, no matter how simple the rules, order is emergent, not predictable.

  • Jurgen Appelo

    Sonja, thanks for the example!

  • Brad Appleton

    Hi Jurgen! Have you seen the Cynefin framework! It too uses the terms complicated, complex, simple and chaotic and is based upon CAS theory. Take a peek at and (especially the resources section)

  • Jurgen Appelo

    Brad, thanks for the link!


    I am reminded of chaordic design process. That place between chaos and order where emergence happens. Dee Hock coined this term in the book, Birth of the Chaordic Age. We can intentionally design from this place. New life comes from the unknown and we want to nurture that place where innovation begins to take form, we cannot control this to the point of killing it off…so dancing the chaordic dance is a practice of mine. I highly recommend checking out some of the writings on Appreciated this blog post!

  • LJFurman

    A bullet is simple.
    A semi-automatic gun is complicated.
    A semi-automatic in the hands of a human firing bullets into other humans leads to complex and chaotic events, such as the tragic events in Tuscon, Arizona, Jan. 15.
    We can get into real trouble when we think a complex problem has a simple solution. Consider the U. S. wars in Viet Nam, Iraq and Afghanistan.

  • LJFurman

    A more fun description –
    Simple – a snowboard.
    Complicated – standing on a snowboard.
    Complex – riding a snowboard down a mountain.
    Chaotic – falling ….

  • Craig

    Your diagram “The spectrum of process complexity” has the word Anarchy, where a more reasonable person would put Chaotic.
    Anarchists would dispute that an anarchic state is chaotic. Anarchy is a system where each individual makes their own decision on what to do, including decisions to co-operate for the common or personal good. Rules on “Do unto others” are necessary to limit actions that negatively impact on others. In the real world, there are some enlightened state constitutions do allow citizens a lot of personal freedom, limiting it where it impacts others, but no state yet permits full personal choice.

  • Jurgen Appelo

    Thanks, but it’s not my diagram. It’s Ralph Stacey’s diagram.
    I have a new blog post about it here:

  • Dibyendu De

    Loved this post except for the fact that chaos is not ‘disorder’ as pictured. Chaos also has deterministic order and it can be predicted by its governing rules and principles.

  • Kevin Earle

    Hmm. A bullet is simple-ly useless without a weapon to fire it from.
    A firearm maybe complex in construction but simple-ly uncomplicated to use.
    Chaos may come upon us but be resolved by the simple solution of using a firearm in defense.
    The human society may appear as chaotic as an ant nest, yet in reality humans are uncomplicated in their complexity. Then they marry.

  • Bob Ross

    So life never evolved? Life has always been complex right from the start? Life just instantly came into existence at some point in time?

  • Bob Ross

    So life did not evolve from a simple system of some sort? It was always and instantly at least a complex system?

  • Jurgen Appelo

    How could I answer this question? Nobody knows how life came into existence.

  • Bob Ross

    Can a simple system ever increase its complexity by interacting with another system?

  • Edree Allen-Agbro

    Having driven in Lagos Nigeria in a Volkswagen years ago, I appreciate your analogy.
    As a “soft skills geek” who teaches leadership skills to IT managers, it is interesting moving from the simple content ideas to the complexity of putting them into practice. Temporary chaos is the typical result of the “simple” tasks like becoming aware of and articulating feelings as well as ideas. Ironically, computers are being programed to detect and relate appropriately and ethically to user emotions. It seems our relationship with the technology we create is quite complex.

  • salvatore angelone

    A complex structure like the universe is very complicated to explain. So is a car (though not as complex as the universe), a gun, a pizza, or mukhwas or software development. They are forever interwined. Chaos occurs when a complex system is interpreted and codified by an idiot and people collectively call it common sense. Complicated systems are more susceptible to a comedy of errors as a result of things like their tight structuring and rigidity of staying the course. I’m fairly certain that is why we humans have free will. To forever complicate the shit out of everything is a human condition.

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