Van der Maas and the leap
On a Dutch psychologist who showed that development is sometimes better described as a leap than as gradual growth.
Han van der Maas is, in our view, one of the influential names in Dutch developmental psychology research. In the 1990s and 2000s he worked out an idea that seems simple at first sight but became the basis of an entire research programme: development does not always proceed gradually; sometimes it proceeds in leaps.
That may sound self-evident, but in a field that had until then mainly described cognitive development as steady growth (first this, then that, then the next), it was a substantial contribution. Together with Peter Molenaar, Van der Maas argued that many cognitive transitions, for instance in conservation tasks, language acquisition and rule understanding, can be described as catastrophe leaps: the system does not glide gradually into a new state, it tips.
What is a catastrophe leap?
The term comes from mathematics, from René Thom's catastrophe theory of the 1960s, and is technical in nature. Fortunately the core idea is easy to follow. Some systems have two states in which they can remain stable. When an underlying parameter (maturation, practice or age, for example) changes slowly, the system at first stays in its old state. Only when a threshold is reached does it tip, rather suddenly, into the new state.
A fine example that Van der Maas used is learning to conserve: the insight that the quantity of water stays the same when it is poured into a different glass. Some time before children master this, they begin to hesitate. They give inconsistent answers and seem to sense that there is something they do not yet fully understand. Then, often within a short period, it tips: they understand, and that insight stays.
Why this matters
First, it seems to describe better what we sometimes see in practice. Parents, teachers and clinicians working with children will recognise it: a child who is stuck for a long time and then suddenly picks something up. This need not be because the practice announced it; it may also be that the system was ready to tip.
Second, it offers language for something that otherwise remains puzzling. The leap is then no miracle but a property of certain dynamical systems under certain conditions. That makes it, in principle, open to investigation.
Third, it has consequences for how we measure. A time series just before a leap can have characteristic properties: increasing variance, slower recovery after a perturbation and a longer "memory" of the system. These are called "early warning signals" (see also the lexicon entry). Noticing tipping points therefore requires different measurements from those needed merely to compare averages.
The bridge to clinical practice
Put cautiously, this way of thinking is also meaningful for mental health care. Sudden gains (the abrupt symptom improvements observed in many psychotherapies) resemble such tipping points in their structure, and the same holds for relapse after a long remission.
A clinician who pays attention to this sometimes sees early signs: more day-to-day variability, disrupted sleep, unrest in a patient's attachment relationships. That is not always the case, and such signs are not always interpreted correctly; sometimes noise is simply noise. Still, the idea that a system can move towards a tipping point offers, in our impression, useful points of departure for clinical attention.
A modest balance
Over the past decades Van der Maas and his colleagues have done much valuable work to ground these ideas empirically. The evidence for catastrophe leaps in cognitive development is, in our view, more robust than in the clinical context. There we often still speak in terms of "could" and "resembles".
As an aid to interpreting what we sometimes think we observe in the consulting room, however, the idea seems valuable to us. Not all change proceeds gradually. Sometimes someone is stuck for a long time and then suddenly no longer. That we now have a name and a cautious mathematical grounding for this helps us to take such moments seriously, both for ourselves and together with our patients.