Simple · Complicated · Complex
Three words that resemble one another but reside in three different worlds of thought.
The difference between simple, complicated and complex may seem small, but it determines what kind of thinking one brings to care — and which methods belong to that thinking.
Simple is what the secondary-school physics lesson still kept tractable. Push a block, and it moves. Push harder, it moves faster. Open a tap, and water flows. Cause-and-effect relations are clear and approximately linear: more of this gives more of that.
Complicated is a clock, an aeroplane, a diesel engine. Many parts, yet predictable once one knows the rules. One may take it apart, study each part, and reassemble it without the logic going lost. The whole is the sum of its parts. Cause and effect remain, in principle, traceable.
Complex is another animal. Many parts, yes, but they interact in non-linear ways — and from those interactions emerge properties that cannot be predicted from the sum of the parts. An ant in an anthill. A neuron in a brain region. A person in a social system. Pull it apart and one holds in one's hands something that is no longer alive.
What this means for psychology
Van der Maas (2024) places psychology unambiguously in the third category. A fear response may lead to flight, but also to attack. Whether a stimulus is experienced as threatening depends on context, on the state of the person, on history. It may differ from second to second. And a calm situation may suddenly tip into panic — without the stimulus changing radically.
"In psychology, cause-and-effect relations are rarely simple, and effects are often non-linear." — Van der Maas (2024)
This has consequences. In mental health care we have developed many diagnostic and treatment methods that implicitly assume a complicated model — as if components can be addressed apart from one another, and as if the sum of interventions leads to recovery. For some problems this works reasonably. For most — depression, anxiety, personality, eating disorders, addiction — it works only halfway. Not because the methods are poor, but because the type of system we treat is not complicated but complex.
Other methods for a different type of system
Working with complex systems calls for other methods: measuring patterns over time, recognising transitions, treating context as an integral part of treatment, and accepting that trial-and-error and responsiveness are not signs of unprofessionalism, but of a healthy engagement with a system that does not let itself be dissected.
It is a form of professional modesty to make this distinction. It need not lead to despair — we can certainly influence a complex system, only not predict or steer it in the manner in which we can steer a complicated one. It is working on a system that talks back.