"A jumbo jet is complicated, but mayonnaise is complex..."

As I've mentioned a few times in the last several posts, I've been doing a lot of reading about chaos theory and complexity theory lately.  These two topics are highly interrelated and absolutely fascinating.  I've never fully appreciated the subtle differences between complex systems and merely complicated ones.  Let me explain.  Just take a look at the Merriam-Webster Dictionary definitions of complex versus complicated below:

Complex - a group of obviously related units of which the degree and nature of the relationship is imperfectly known; hard to separate, analyze, or solve

Complicated - consisting of parts intricately combined; difficult to analyze, understand, or explain

They sound fairly similar, right?  Both terms are often used interchangeably, at least in an everyday kind of context.  However, when it comes to complexity theory, the two terms are quite distinct.  Mary Uhl-Bien and Michael Arena have written extensively on the kind of leadership required in complex systems, and in one of their articles ("Complexity leadership: Enabling people and organizations for adaptability"), they provided what I think is the best characterization of the differences between complex systems and merely complicated ones.  They wrote, "… a jumbo jet is complicated but mayonnaise is complex. When you add parts to a jumbo jet they make a bigger entity but the original components do not change–a wheel is still a wheel, a window is a window, and steel always remains steel. When you mix the ingredients in mayonnaise (eggs, oil, lemon juice), however, the ingredients are fundamentally changed, and you can never get the original elements back. In complexity terms, the system is not decomposable back to its original parts…"

As Alex Di Miceli explains in a blog post on Medium ("Complex or complicated?"), complex systems are emergent, meaning that the whole is always greater than the sum of its parts.  Like the mayonnaise, you can't break complex systems down into their individual components easily and figure out how they work together.  Complicated systems are not emergent, so you can break these systems down into their individual components rather easily and see how they fit and interact together.  He writes further:

"A car engine is complicated, traffic is complex."

"Building a skyscraper is complicated. The functioning of cities is complex."

"Coding software is complicated. Launching a software startup is complex."

To the same extent, nerve cells are complicated, but the brain is complex.  Ian Stewart, who co-wrote a book called The Collapse of Chaos: Discovering Simplicity in a Complex World with Jack Cohen, once said, "If our brains were simple enough for us to understand them, we'd be so simple that we couldn't."