When the direction of casual influence extends from "higher" levels of reality (say, above the level of physics) down to "lower" levels of reality, it is called downward causation. The ontological structure of the world may be seen as consisting of more than one domain, with each domain consisting of different entities, and with different properties defined over the respective domains. Thus Cartesian dualism envisaged a bifurcated world of two metaphysically independent domains, one containing mental substances defined by "thought" or "consciousness," and the other containing physical "stuff" defined by "extension." In contemporary emergentism the world is pictured in terms of a multilayered structure, with microphysical entities at the bottom and with higher-level entities (such as molecules, cells, organisms, and social groups) being mereologically composed of these lower-level entities, yet characterized by a set of properties distinctive of the relevant higher level. In a way, so-called nonreductive physicalism, which more or less became the received view in the philosophy of mind of the last quarter of the twentieth century, may be seen as nothing but a modern application of classical emergentism within the philosophy of mind. Although it holds that, ontologically speaking, all there is are physical entities and mereological aggregates thereof, it argues that psychological properties are irreducibly distinct from the underlying physical and biological properties.
Regarding such stratified ontologies, two questions naturally arise. First, there is the question of whether higher-level processes may causally interact amongst each other. Secondly, there is the closely related question of whether higher-level processes may also exert "downward" causal influence on events occurring at lower-levels of reality. Indeed, this so-called downward (or top-down ) causation may hold special interest from a theological perspective, since the very possibility of divine action may plausibly be seen as dependent on the possibility of downward causation. It has been argued that the first question inherits whatever problems may attach to the second, which is the more crucial of the two. Thus Jaegwon Kim has claimed that same-level causation can occur only if cross-level causation can occur. Accordingly, downward causation is essential to most of the stratified ontologies under consideration.
The concept of downward causation allegedly runs into serious difficulties. Specifically, there are problematic implications of the idea implied in downward causation; for example, that higher-level processes, once having emerged from lower-level physical processes, biological processes, and so on, would somehow take on a causal life of their own down to the point of actually interfering in the underlying chain of physical causes and events. If, say, emergent mental properties are irreducibly distinct from physical properties (as maintained in emergentism and non-reductive physicalism alike), and if instances of these mental properties may be independent higher-level causes and effects of lower-level physical (e.g., bodily) events, then some physical events cannot be fully explained in terms of physical antecedents and laws alone. This result, however, would violate two highly respected and important philosophical principles: the principle of the causal closure of the physical domain and the closely related principle of the completeness of physics. That is to say, assuming causal interaction between higher-level processes on the one hand and processes at the basic level of physics on the other (as presupposed in all of the above philosophies with stratified ontologies), there can no longer be a complete physical theory of physical phenomena.
An alternative account of the relation between various ontological levels may be possible, allowing one to avoid the above dilemma. Levels of reality are not just related by the mereological relation of being part of. That would render organisms mere aggregates of cells, and cells mere aggregates of molecules. In addition they are related by higher-level principles organizing lower-level events into systemic patterns of interaction. As a result, certain context-dependent causal pathways of physical activities will be selectively activated, rather than others. In view of this alternative relationship of socalled multiple supervenience, causal processes may come to be seen as highly patterned systemic processes discernible only at higher levels of reality.
Reflecting upon this relationship of multiple supervenience may thus make clear that higher-level patterns of organization are themselves genuine causal factors actually operative in channeling and orchestrating the lower-level flux of microphysical events to yield stable recurrent patterns of macrocausation that are self-sustaining or self-reproducing as a result of the systemic organization of their parts. In other words, given multiple supervenience, downward causation will occur in consonance with the principles of physics, rather than in violation of them. To believe in downward causation, therefore, need not be tantamount to a belief in brutely emergent fundamental laws proprietary to a certain level of intricately organized systems of physical events and processes, such as organisms or minds, with concomitant causal interference at lower levels of organization in violation of the laws of microphysics. Hence, downward causation may be assigned a stable place in the picture of how the world is organized without upsetting the conception of the various domains of physics as constituting a closed and complete system of physical events at the physical level of description.
See also Causality, Primary and Secondary; Causation; Divine Action; Physicalism, Reductive and Nonreductive; Supervenience
kim, jaegwon. "'downward causation' in emergentism and non-reductive physicalism." in emergence or reduction? essays on the prospects of nonreductive physicalism, ed. ansgar beckermann, hans flohr, and jaegwon kim. berlin: walter de gruyter, 1992
kim, jaegwon. "the non-reductivist's troubles with mental causation." in mental causation, ed. john heil and alfred mele. oxford: oxford university press, 1993
meyering, theo c. "mind matters: physicalism and the autonomy of the person." in neuroscience and the person, ed. robert john russell, nancey murphy, theo meyering, and michael a. arbib. berkeley, calif.: vatican observatory and center for theology and the natural sciences, 1999
meyering, theo c. "physicalism and downward causation in psychology and the special sciences." inquiry 43 (2000): 181–202.
theo c. meyering