Levels, Emergence, and Three Versions of Downward Causation
by Claus Emmeche*, Simo Køppe** and Frederik Stjernfelt***
Medium Downward Causation
A wheel running downhill.
what explains the
rolling movement?
... the lower levels
... the form of the wheel. The higher level performs a function irreducible to the lower.
If we take a neuropsychological example and try to explain the origin of some state of consciousness from the state of the nervous system, then the only consistent interpretation of Sperry's point of view is that a given state of consciousness is chosen among a series of states of consciousness made possible by the nervous system at a certain moment. The decisive point in this choice of state of consciousness lies on the higher level, in this case the psychical level. It is the previous states of consciousness which determine or select which one of the possible states of consciousness should be realized. Hence the interactionism; the interaction between the manifested states of consciousness decides which possibility is to be realized.
Medium downward causation can be defined as follows: an entity on a higher level comes into being through a realization of one amongst several possible states on the lower level -- with the previous states of the higher level as the factor of selection. This idea can be made more precise with the aid of an interpretation of the concept of "boundary condition."
This concept is primarily used in physics and mathematics. Mathematically, the boundary condition is the set of selection criteria by which one can choose one among several solutions to a set of differential equations describing the dynamics of a system.
[12] In classical mechanics, a system's initial conditions are defined as the set of parameters describing the starting point of a system at a certain moment and which -- measured with sufficient precision -- may form the basis for the calculation of an, in principle, unlimited predictionof the system's behaviour. In complex physical phenomena it is supposed that certain changes in initial conditions make central properties in the dynamics change; these are named boundary conditions because they delimit the set of initial conditions within which the properties in questions will be found. In this context the concept does not entail the assumption of levels.
//p. 25/
In relation to level theories, boundary conditions are conceived as the conditions which select and delimit various types of the system's several possible developments. The realization of the system implies that one of these typical developments is selected, and the set of initial conditions yielding the type of possibility chosen are thus a certain type of boundary condition which has been called constraining conditions. They only exist in complex multi-level phenomena on a level higher than the focal level, and are the conditions by which entities on a high level constrain the activity on the lower focal level.
[13]
On this basis, medium downward causation can be reformulated as follows: higher level entities are constraining conditions for the emergent activity of lower levels. And -- hence the Sperry example -- in a process, the already realized higher level states are constraining conditions for the coming states.
How are we to understand the nature of this constraint? One interpretation is to say that the higher level is characterised by organizational principles -- lawlike regularities -- that have an effect ("downward," as it were) on the distribution of lower level events and substances.
- Thus, if, for instance, evolution by natural selection is such a lawlike regularity, we can only understand the physical distribution of energy and matter in a ecosystem if we consider the effect of natural selection on frequencies of genotypes, and thus on the phenotypes of the various existing organisms, which themselves influence the cycles of matter and energy in the system. This interpretation of medium DC is close to the view of Campbell (1974).
In contrast to weak downward causation, medium downward causation is characterised by this claim; even if no law-breaking influence top down is admitted, the higher level constrains which higher level phenomenon will result from a given lower level state. Thus, the radical forms of dualism or vitalism of strong downward causation is avoided at the expense of a less radical idea that the same lower level constituents may correspond to a series of different higher level phenomena.
In contrast to strong DC, medium DC does not involve the idea of a strict "efficient" temporal causality from an independent higher level to a lower one, rather, the entities at various levels may enter part-whole relations (e.g., mental phenomena control their component neural and biophysical sub-elements), in which the control of the part by the whole can be seen as a kind of functional (teleological) causation, which is based on efficient, material as well as formal causation in a multinested system of constraints. The kind of determinative relation between part and whole is not quite clear, and the term "interaction" is according //p. 26/ to Sperry (1987) not the best for the kind of relationship envisaged.
[14] Thus, "Mind is conceived to move matter in the brain and to govern, rule, and direct neural and chemical events without interacting with the components at the component level, just as an organism may move and govern the time-space course of its atoms and tissues without interacting with them" (Sperry 1987).
We have to differentiate between the following two assumptions. (a) Higher level entities function as criteria for the selection of lower level emergent processes. The higher level entities constrain the development of lower level processes in accordance with the history of the level. (b) One set of entities at a lower level can be the starting point for different entities at the higher level. This is a sort of inverse supervenience. One can, for the sake of the argument, assume that two organisms consist of the same amount of different substance -- but are very different organisms. This conclusion rests on the premise that the levels already exist -- they cannot be used to describe or explain the development of levels.