Reductionism can be defined as the belief that the behavior of the whole is
completely determined by the behavior of the parts. In other words, if you
know the laws governing the behavior of the parts, you should be able to
deduce the laws governing the behavior of the whole.
Systems theory has always taken an anti-reductionist stance, noting that
the whole is more than the sum of the parts. In other words, the whole has
"emergent properties" which cannot be reduced to properties of the parts.
Since emergence is a rather slippery concept, which has been defined in
many different ways, most of which are highly ambiguous or fuzzy, I prefer
to express this idea with a more precise concept: downward causation.
Downward causation can be defined as a converse of the reductionist
principle above: the behavior of the parts (down) is determined by the
behavior of the whole (up), so determination moves downward instead of
upward. The difference is that determination is not *complete*. This makes
it possible to formulate a clear systemic stance, without lapsing into
either the extremes of reductionism or of holism: the whole is to some
degree constrained by the parts (upward causation), but at the same time
the parts are to some degree constrained by the whole (downward causation).
Let me illustrate this with an example. It is well-known that snow crystals
have a strict 6-fold symmetry, but at the same time that each crystal has a
unique symmetric shape. The symmetry of the crystal (whole) is clearly
determined by the physico-chemical properties of the water molecules which
constitute it. But on the other hand, the shape of the complete crystal is
not determined by the molecules. Once a shape has been formed, though, it
are the molecules in the crystal that are constrained: they can only be
present at particular places allowed in the symmetric crystalline shape.
The whole (crystal) constrains or "causes" the positions of the parts
(molecules).
The appearance of this "two way causation" can be explained in the
following way. Imagine a complex dynamic system. The trajectories of the
system through its state space are constrained by the "laws" of the
dynamics. These dynamics in general determine a set of "attractors":
regions in the state space the system can enter but not leave. However, the
initial state of the system, and thus the attractor the system will
eventually reach is not determined. The smallest fluctuations can push the
system either in the one attractor regime or the other. However, once an
attractor is reached, the system loses its freedom to go outside the
attractor, and its state is strongly constrained.
Now equate the dynamics with the rules governing the molecules, and the
attractor with the eventual crystal shape. The dynamics to some degree
determines the possible attractors (e.g. you cannot have a crystal with a
7-fold symmetry), but which attractor will be eventually reached is totally
unpredictable from the point of view of the molecules. It rather depends on
uncontrollable outside influences. But once the attractor is reached, it
strictly governs the further movement of the molecules.
The same principle applies to less rigid, mechanistic systems such as
living organisms. You cannot have organisms whose internal functioning
flouts the rules of physics and chemistry. However, the laws of physics are
completely insufficient to determine which shapes or organizations will
evolve in the living world. Once a particular biological organization has
emerged, it will strongly constrain the behavior of its components.
For example, the coding of amino acids by specific triplets of bases in the
DNA is not determined by any physical law. A given triplet might as well be
translated into a multitude of other amino acids than the one chosen in the
organisms we know. But evolution happens to have selected one specific
"attractor" regime where the coding relation is unambiguously fixed, and
transgressions of that coding will be treated as translation errors and
therefore eliminated by the cell's repair mechanisms.
A final example from the cultural sphere. Although our basic measuring
units (e.g. second or meter) are defined by physical means (e.g. through
the invariant length of a particular wave lenght of a particular type of
electromagnetic radiation), the specific choice of unit is wholly
arbitrary. The laws of physics impose the constraint that the wave lenght
of light emitted by a particular quantum transition as measured in the
units we choose must always be the same. However, the choice of a
particular unit is not determined by those laws of physics. It is the
result of a complex socio-cultural evolution in which different units are
proposed for the most diverse reasons, after which one unit is eventually
selected, perhaps because it has been used a little bit more frequently by
slightly more authoritative sources than the other ones. Once the standard
gets established, it becomes a constraint which everybody is supposed to
follow. The whole (the socio-cultural system with its standards) determines
the behavior of the parts (the measurements made by individuals).
________________________________________________________________________
Dr. Francis Heylighen, Systems Researcher fheyligh@vnet3.vub.ac.be
PESP, Free University of Brussels, Pleinlaan 2, B-1050 Brussels, Belgium
Tel +32-2-6292525; Fax +32-2-6292489; http://pespmc1.vub.ac.be/HEYL.html