Recursivity
When the output of one step becomes the input of the next — and the system acts upon itself.
Recursivity, or iteration, denotes the phenomenon that the components of a system act back upon one another: the output of an operation becomes the input of the next. Through this repeated feedback, sequences of states arise that issue from the action of operations upon operations.
It is one of the quiet engines behind complex behaviour. Chaos, Schiepek notes, results from the interconnection of components that act recursively upon one another. Three things are required for this: mixed feedback — positive and negative feedback working together — at least some non-linearity in the interaction, and a minimal value of a relevant control parameter. Where these conditions meet, a system can let astonishingly rich behaviour arise from simple, repeated rules.
Self-feeding patterns
In the clinical context recursivity makes intelligible why some patterns are so persistent. A thought feeds a feeling, which calls up a behaviour, which confirms the original thought — and the loop is closed. No single link is the cause; it is the feedback itself that keeps the pattern in place. Those who are stuck are often, to our impression, caught in just such a self-feeding circle.
At the same time this very insight offers hope. A recursive pattern can also tip for the better: if one link changes durably, the whole loop may reorient. This explains 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.