Emergence
Why parts do not always explain what the whole does — and why that is not a problem.
More is different. With this title the physicist Philip Anderson published in 1972 an essay that to this day appears foundational for thinking about complexity. Sometimes a whole is more than the sum of its parts — and that more, to our minds, is essential for what we wish to understand.
Emergence is the phenomenon that properties appear at a higher level of description which are not present at the lower levels. Magnetism does not exist in a single atom. A traffic jam is not a property of one car. Consciousness is not a property of one neuron. Yet they arise, reliably, from the interaction between those parts.
Weak and strong emergence
Philosophers distinguish two kinds. Weak emergence is the "innocent" variant: the higher level is a useful description, but in principle reducible to the lower. A traffic jam is, ultimately, a group of cars with velocity and position. That we describe the jam as a thing is a useful shorthand, not an ontological claim.
Strong emergence goes further: the higher level has its own causal power, not fully reducible to the parts. The predator reacts to the flock, not to the individual birds — and thus the flock-as-flock influences the behaviour of the birds. This is called downward causation: the whole influences its parts. For psychology this is less esoteric than it sounds. A depression is more than the sum of its symptoms — it in turn influences which symptoms amplify.
"Science is possible at many different levels of description without our having to fully understand the lower levels." — Van der Maas (2024), after Fodor (1974)
Why this matters for mental health care
The implicit logic of much clinical thinking is reductionist. We look for the "real" cause of complaints at a lower level: a neurotransmitter imbalance, a genetic predisposition, a brain circuit. Sometimes that yields. But often — in depression, anxiety, personality, eating disorders — we find at the lower level no clean cause that fully explains the complaint.
The emergence approach says: that is not a problem. Much psychopathology is an emergent property. It arises from the interaction between biology, cognition, behaviour, context and relationships. The depression "lives" at a level of description that is real, even though it has no single biological marker. Just as a traffic jam is real without there being a "jam particle" in an individual car.
This has implications for diagnostics and treatment alike. We do not first have to find the "real" level of the complaint in order to be able to do something about it. Interventions at a higher level (behaviour, social context, meaning-making) may be entirely legitimate — not as a surrogate for the "real" treatment, but as interventions at the level at which the problem actually forms itself.
A reassurance and a challenge
Emergence gives psychology its right to exist as a science. We need not wait for neuroscience to be "finished" before thinking about depression or anxiety. At the same time, thinking from emergence demands more from us: we must learn to work with several levels at once, and to know which level offers the most illumination for which problem.
For this reason, complexity science is not anti-biology or anti-neuroscience. It is a complement — a way of doing justice to the fact that psychological problems, like traffic jams and flocks and consciousness, often live on several levels at once, and are approachable on several levels at once.