Belief in
causality is deeply held by many philosophers and scientists. Many say it is the basis for all thought and
knowledge of the external world. The idea that
every event has a cause leads to the view of
causal closure or causal
determinism. The simplest form of physical determinism is the
Laplacian view that given the positions and velocities of all the fundamental particles in the world, together with the laws of nature, that there is only one possible future.
Reductionism is the view that material particles and the physical forces between them, which are supposed to be mathematically analytical, can explain all that happens in the world. Chemistry is thought to be reducible to physics, biology reducible to chemistry, psychology (via neuroscience) reducible to biology, and mind/brain (or cognitive science) reducible to psychology. All these causal relations are called "bottom-up."
The finest details of brain events are thought by some to be a consequence of motions of the material particles that comprise the brain. Reductionism implies that mind is an
epiphenomenon, or worse, just an
illusion. The reductionist idea that everything is the consequence of "bottom up" physical causes is often called
eliminative materialism.
By contrast,
downward causation is a kind of
holism that denies
reductionism. "Wholes" can enforce constraints on their "parts" to make them move in ways that may be unpredictable, even given the complete information about the parts (ultimately the atoms and molecules) along with the complete information about the state of the universe outside those parts.
Downward causation is closely related to the concepts of
emergence,
self-organization, and
supervenience. It has become very popular in the study of complex physical systems which exhibit a kind of self-organization and emergence of visible structures when the systems are far from equilibrium conditions.
Most modern discussions of emergence and self-organization in hierarchical systems start with the early 1950's work of
Ilya Prigogine on
dissipative structures, physical and chemical systems that are far from equilibrium, through which there is a steady flow of matter and energy.
Despite the normal tendency to chaos (the second law of thermodynamics and increasing entropy), these dissipative systems develop relatively stable visible structures, such as Bénard convection cells and Turing autocatalytic reactions that show space-dependent, steady-state processes stable against perturbations. These visible structures reduce the entropy locally. They are "information structures" of a very simple kind.
Prigogine's discovery of such "order out of chaos" in physical systems is widely cited as evidence of
emergent properties in
complex adaptive systems. It lies at the heart of modern
complexity theory and
chaos theory. But these complex and chaotic information structures are "dumb." They do not contain the internal
information processing that marks the emergence of life and mind. These two higher-level emergent information structures are "smart," by comparison. When they exert downward causation, it is extraordinarily
fine.
The idea that emergent structures can exert a sort of "holistic" downward causal control on their molecular components was first articulated by
Roger Sperry in 1965. Sperry cites a wheel rolling downhill as an example of downward causal control. The atoms and molecules are caught up and overpowered by the higher properties of the whole. Although this is a very
gross kind of control over the components, Sperry says that he "worked the new mind-brain ideas into a discussion of holist-reductionist issues, emergent downward control. and ‘nothing but’ fallacies in human value systems, in a broad refutation of the then prevalent ’mechanistic, materialistic, behavioristic, fatalistic, reductionistic view of the 'nature of mind and psyche’."
In 1974
Donald Campbell coined the phrase "downward causation" and he is widely cited in the current literature as the main source of the idea.
Some biologists (e.g.,
Ernst Mayr) have argued that biology is not
reducible to physics and chemistry, although it is completely consistent with the laws of physics. Even the
apparent violation of the second law of thermodynamics has been explained because living beings are
open systems exchanging matter, energy, and especially information with their environment.
Information is neither matter nor energy, but it needs matter for its embodiment and energy for its communication.
A living being
is a form through which passes a flow of matter and energy (with low or "negative" entropy, the physical equivalent of information). Genetic information is used to build the information-rich matter into an overall information structure that contains a very large number of hierarchically organized information structures.
Emergent higher levels exert
downward causation on the contents of the lower levels.
The problem of
mental causation is a specific case of downward causal control that is central to the philosophy of mind.
The idea that minds have powers "over and above" the known physical, chemical, and biological laws is sometimes called "
mentalism." It is related to the idea of "
vitalism," that biology might involve new laws that cannot be reduced to "nothing but" the laws of physics.
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