Recursivity
When the outcome of one step becomes the input of the next, and a system thus begins to act upon itself.
Recursivity, or iteration, refers to the phenomenon that the components of a system act upon one another through feedback: the outcome of one operation becomes the input of the next. Through this repeated feedback, sequences of states arise that result from operations acting upon operations.
Recursivity is one of the quiet engines behind complex behaviour. Chaos, Schiepek observes, arises from the interconnection of components that act recursively upon one another. Three things are needed for this: mixed feedback, in which positive and negative feedback work together; at least some non-linearity in the interaction; and a minimal value of a relevant control parameter. Where these conditions come together, a system can produce surprisingly rich behaviour from simple, repeated rules.
Self-feeding patterns
In the clinical context, recursivity helps us understand why some patterns are so persistent. A thought feeds a feeling, that feeling calls up behaviour, and that behaviour confirms the original thought: the circle is closed. None of the links is in itself the cause; it is the feedback that keeps the pattern in place. People who are stuck are, in our impression, often caught in just such a self-feeding circle.
At the same time, the same insight offers hope. A recursive pattern can also tip for the better: when one link changes lastingly, the whole circle can take a different direction. This may explain why a seemingly small but sustained shift sometimes has an unexpectedly large effect, and why timing, the moment at which an intervention touches the circle, matters so much.