Structural coupling is, system-theoretically, the substitute theory for causality. As no person can think in the head of another, it must be explained how people (=psychological systems) influence each other, or how they can even be in connection. The explanation of system theory is that the systems alternatively make their ‘complexity’ available to each other. This sounds rather mysterious. Simply put, what is meant is that no system can maintain itself without internally processing environmental events. In addition, to pick up the example one more time, no person could think if there were no language and he does not develop language by himself, rather, it is delivered in childhood (P. Fuchs). Therefore, people react to language, i.e. they are spoken to. However, no matter what the other party says, he cannot dictate what the receiver thinks as a response, nor does it ultimately determine what happens.
At the same time, the psychological system is relieved of complexity because it cannot pick up upon that which is being said in the frequency area of ultrasound (unlike dolphins or whales). Through the limitation and the selection of coupling possibilities and coupling readiness, systems also become that which they make out of themselves: one always notices when he is criticised, the other never notices at all.
When studying systems, one should always keep in mind the nature of the coupling to the environment. This is elementary for an understanding of change, because particularly through this the possibilities of coupling modifications can be examined.