Chapter 2: Kim’s causal exclusion argument against non-reductivism
2.4 Exclusion and no overdetermination
2.4.5 Genuine inter-level overdetermination and physicalism
Let’s see what follows from these insights to the case of inter-level overdetermination in the context of physicalism. As we saw, sometimes we are only interested in the cumulated effects of certain causes. The effect of pain on our behaviour could be a relevant case. Based on experience, we usually think that the amount of pain experienced is roughly proportional to the amount of crying and yelling that results. The amount of pain received from two sources, must be greater than the pain received from only one of those sources and has to have an increased effect on our yelling and crying compared to receiving pain only from one of those
sources. If there was mental-physical overdetermination it would have to work similarly. Physical effects of mental pain like crying and yelling are caused both by the mental state and its physical realizer and more pain means more crying.
Now, imagine that a group of neuroscientists make experiments to figure out the level of certain neural activities (the realizers of pain) with the amount of yelling and crying. Their results show the same relation as the relation we can measure between the feeling of pain and yelling. In case neural and mental causes are both real causes of the outcome, in the sense required by everyday examples of overdetermination, we should suppose that the measured crying and yelling experienced results from the independent contributions of two causes, mental pain and neural activity.
Any of the two token causes could trigger a certain amount of crying and yelling alone, but the mental and the physical cause together should cause more of the crying and yelling than what one of those cases would trigger alone simply because under normal circumstances the effects of pain accumulate. From this it follows that the accumulated physical effect of a mental and a physical cause together is not sufficiently caused by the physical cause of the same effect alone.
Because of the supervenience relation between levels there is no way to check empirically whether mental causation really does involve overdetermination or not. In our world the realizer and realized causes always go together, so the same effect is measured both by neuroscientists using brain scans and traditional psychologists, probably using a survey-based qualitative approach to measure mental pain. Therefore, there are no empirical means to decide this issue. However, what I have shown above is that whatever we measure as the effect of inter-level redundant causes, the measured effect has to have two real
components that both make a difference to the physical goings on in terms of the cumulated effect.
This result is surely unacceptable for physicalists. It flies in the face of the causal closure principle which is at the core of physicalism. According to the causal closure principle all physical effects are sufficiently caused by other physical events alone. However, the cumulated effect brought about by inter-level overdetermination is not sufficiently caused by purely physical causes. Therefore, inter-level overdetermination cannot be reconciled with physicalism.
Is there a possible answer to this argument? Can’t we simply utilize the strategy based on disanalogies between intra-level and inter-level overdetermination? It is not impossible that the difference between cumulated and threshold effects exists only in intra-level cases and there are no cumulated effects for inter-level overdetermination? This is more or less one of Schaffer’s (2003) answers to arguments by Bunzl (1979). He insists that we should accept the option according to which excess effects of redundant causes can simply disappear into thin air. “As any child can attest, we have perfectly clear intuitions about causation involving spell castings, and other fairy tale devices” (Schaffer 2003:27). To say this, Schaffer has to presuppose that spells can overdetermine outcomes without producing excess effects, or, in other words, anything more than the exact threshold effect itself. Maybe this is not true in our world, only in some far away possible world with different laws. So, it may be a possibility. But there is a further price to pay for choosing this solution. It increases the level of ad hocness involved in the defence of systematic inter-level overdetermination.
First, it is an ad hoc move, as it is utilized only to save mental causation. Second, it is an unparsimonious solution, as it still results in endless dysfunctional excess causes for effects in our universe. Third, the solution is even more ad hoc, because such kind of systematic inter-
level overdetermination is too unlike other cases of overdetermination. They are different from other cases in terms of the relation between the redundant causes involved which was required for explaining the systematic nature of this kind of overdetermination, and also in not having cumulated effects. Combining this with the other reasons amounts to a strong reason to reject this deviation.
By the argument above I have provided strong grounds for rejecting inter-level overdetermination in the context of physicalism. The argument based on the distinction between threshold and cumulated effects provides motivation for rejecting any kind of real inter-level overdetermination, as it shows that such overdetermination would be in conflict with physicalism. I would summarize these insights in the following way:
No innocent overdetermination*: When a physical effect E is caused by
autonomous overdeterminer causes C and D (where both are sufficient for bringing about E) together, they always create some unique difference in the physical world over and above bringing about E, that is dependent on their joint presence.
This new principle is different from the original idea relied on in other formulations of the exclusion argument. The no overdetermination principle says that overdetermination is rare, so in general the presence of one cause gives a prima facie reason to think that there is no competing cause. The no innocent overdetermination* principle tells us that overdetermination might be a frequent phenomenon, but if it takes place in an inter-level context it cannot be innocent, it would be incompatible with the causal closure of the physical. This provides perfect rationale for accepting the exclusion principle in Kim’s rendition of the exclusion argument (IV in section 2.2.).
As we saw in the section on causal closure (2.3) overdetermination would not be a problem for the emergentist. If there were higher-level emergent properties with autonomous, novel causal powers, the behaviour of a system calculated using only basic physical laws would be different from its actual behaviour (see section 184.108.40.206). The difference between the results provided by such a model and one enriched with trans-ordinal and emergent causal laws is similar to the difference between a world without inter-level overdetermination and one where there is frequent overdetermination by independent causes at different levels.