Jaegwon Kim has spent many years working on the mind-body problem
and the related problem of mental causation
. He has critically examined the concept of supervenience
, the idea that emergent
properties or laws in the higher level of a hierarchy might give them downward causal control
over the properties or laws of lower levels.
Kim generally accepts the idea of physicalism, that the world consists of material particles subject to the known laws of physics. For many thinkers, physicalism implies reductionism
, the idea that all worldly phenomena are reducible to physics. Indeed, today chemistry has largely been reduced to physics, although the properties of even simple molecules like water are generally not predictable from the properties of the component atoms hydrogen and oxygen (as first pointed out by John Stuart Mill
Biology in particular seems to have emergent
properties and laws that are not reducible to physics. Is the molecular biology of a cell reducible
to the laws governing the motions of its component molecules, or are there emergent laws
governing motions at the cellular level, the organ level, the organism level, and so on up to the mental level? If so, then mental causation would be a special example of an emergent level in a hierarchy exerting downward causation
on the components of all lower levels.
The term supervenience
was used by the early emergentists to describe this downward or top-down causation. But if all the levels are made up of physical particles obeying causal laws, Kim asks how can any level escape the "causal closure" implied in the reductionist view of bottom-up causation?
Kim has investigated claims of a "non-reductive physicalism," notably those of Donald Davidson
In his 1970 essay "Mental Events" (in Experience and Theory
, Univ of Massachusetts Press, 1970), Davidson claimed that mental events are anomalous
, they are not (as physical events are) describable by strict deterministic laws that can be used to predict our thoughts. Nevertheless, he believed that mental events can be causally related to physical events. Can he have it both ways?
Davidson admitted he was in sympathy with Immanuel Kant
and might be only explaining away an apparent contradiction between the mental and the physical, resolving a kind of antinomy, and perhaps the paradox of free will?
Davidson describes what he calls "Anomalous Monism" based on three principles:
The first principle asserts that at least some mental events interact causally with
physical events. (We could call this the Principle of Causal Interaction.) Thus for example if someone sank the Bismarck, then various mental events such as perceivings, notings, calculations, judgements, decisions, intentional actions, and changes of belief played a causal role in the sinking of the Bismarck. In particular, I would urge that the fact that someone sank the Bismarck entails that he moved his body in a way that was caused by mental events of certain sorts, and that this bodily movement in turn caused the Bismarck to sink. Perception illustrates how causality may run from the physical to the mental: if a man perceives that a ship is approaching, then a ship approaching must have caused him to come to believe that a ship is approaching. (Nothing depends on accepting these as examples of causal interaction.)
Though perception and action provide the most obvious cases where mental and physical events interact causally, I think reasons could be given for the view that all mental events ultimately, perhaps through causal relations with other mental events, have causal intercourse with physical events. But if there are mental events that have no physical events as causes or effects, the argument will not touch them.
The second principle is that where there is causality, there must be a law: events related as cause and effect fall under strict deterministic laws. (We may term this the Principle of the Nomological Character of Causality.) This principle, like the first, will be treated here as an assumption, though I shall say something by way of interpretation.
The third principle is that there are no strict deterministic laws on the basis of which mental events can be predicted and explained (the Anomalism of the Mental).
The paradox I wish to discuss arises for someone who is inclined to accept these three assumptions or principles, and who thinks they are inconsistent with one another. The inconsistency is not, of course, formal unless more premises are added. Nevertheless it is natural to reason that the first two principles, that of causal interaction and that of the nomological character of causality, together imply that at least some mental events can be predicted and explained on the basis of laws, while the principle of the anomalism of the mental denies this. Many philosophers have accepted, with or without argument, the view that the three principles do lead to a contradiction. It seems to me, however, that all three principles are true, so that what must be done is to explain away the appearance of contradiction, essentially the Kantian line.
To summarize Davidson's arguments:
- "at least some mental events interact causally with physical events"
- "where there is causality, there must be a law: events related as cause and effect fall under strict deterministic laws."
- "there are no strict deterministic laws on the basis of which mental events can be predicted and explained." (mental events are "anomalous.")
Davidson viewed his work as extending that of Immanuel Kant
on reconciling (eliminating the anomalous contradiction between) freedom
. Davidson's rejection of strict deterministic laws for mental events is perhaps consistent with two-stage models
of free will.
Davidson saw supervenience as the last hope for a nonreductive
physicalism, which does not reduce the mental to the physical, the psychological to the neurophysiological. Davidson set two requirements:
- a domain can be supervenient on another without being reducible to it (non reduction)
- if a domain supervenes, it must be dependent on and be determined by the subvenient domain (dependence)
But Davidson also said:
- "supervenience might be taken to mean that there cannot be two events alike in all physical respects, but differing in mental respects"
This threatens to make mental events essentially identical
to physical events. It is hard to see how the mind, if causally determined by the subvenient brain, is not therefore reducible
In Kim's 1988 presidential address to the APA, he said:
The fact is that under Davidson's anomalous monism, mentality does no causal work. Remember: in anomalous monism, events are causes only as they instantiate physical laws, and this means that an event's mental properties make no causal difference.
This is in apparent contradiction with Davidson's first premise above. But Davidson's third premise states that there are no "strict psycho-physical laws." Davidson apparently wants mental and physical events to have causal relations, but without "strict deterministic laws." This may be compatible with two-stage models of free will
, if Davidson thinks of the mental as the anomalous indeterministic free part and the physical as the lawful deterministic will part.
In two-stage models of free will, the first stage generates alternative possibilities
, at least some of which can be randomly generated, so are uncaused. Since they are only thoughts - unrealized, unactualized possibilities - one can describe them, as Kim does, as doing "no causal work."
In his latest book, Kim diagrams Davidson's view of mental events supervening
on physical events, to illustrate his claim that having both
mental and physical causes would be "overdetermination" and thus one is redundant and must be excluded.
- causes -
By causal closure of the physical world, Kim says it is the mental events that are superfluous and must go.
This pure material view of the physical world ignores energy. And most importantly, this view ignores information
, which is neither matter nor energy (though it requires matter for its embodiment and energy for its communication). Information is the modern spirit
Kim says that Davidson's goal of "non-reductive physicalism" is simply not possible. The physical world is "causally closed," says Kim:
what options are there if we set aside the physicalist picture?
Leaving physicalism behind is to abandon ontological physicalism, the view that bits of matter and their aggregates in space-time exhaust the contents of the world. This means that one
would be embracing an ontology that posits entities other than
material substances — that is, immaterial minds, or souls, outside
physical space, with immaterial, nonphysical properties.