Chapter 2: Kim’s causal exclusion argument against non-reductivism
2.4 Exclusion and no overdetermination
2.4.3 Threshold effects, cumulated effects and overdetermination
To formulate a strong argument that works against inter-level, non-coincidental overdetermination, below I will consider how overdetermination scenarios are constructed conceptually. In doing this I am unpacking some underdeveloped comments Kim made (1998:45, 2005:46-48) according to which mental-physical overdetermination would violate the causal closure principle itself.
The first question we should pose is this: how is it possible that two independent, non- overlapping causes are not doing more than one of those causes alone? Only a few authors are cultivating this issue in the causation literature, let alone the mental causation debate, even though it is highly important to have an answer when it comes to supervenience based overdetermination. A useful and plausible suggestion to start with answering the question is that in overdetermination scenarios causal discourse is interested in threshold effects46. A
46 This starting point of mine and the notion of a treshold effect originates from Hausman’s work (1992: 162,
death can be achieved in many ways, can happen in many different ways, but what we humans are interested in is usually whether the threshold we call death was crossed or not.
There are cases where the existence of a threshold is even more straightforward. Imagine a small bowl receiving water from two independent sources. The threshold in this case is crossed when the bowl overflows, so bowl overflow is the threshold effect we are interested in. When there is enough water in the bowl overflow takes place. It is possible to achieve this threshold effect relying on only one source for water inflow, and it is also possible to do that relying on two sources where the two sources contain more water than the one source in the first scenario.
Imagine first that only I poured my full glass of water into the bowl and second that while I was doing the same someone else was pouring another glass that contained less than mine. Bowl overflow takes place in both cases, but there will be a difference that can be measured in the amount of water around the bowl on the table and maybe also on the floor. In the case where there are two sources of inflow more water flows over. This is what causal discourse dismisses as unimportant when the focus is on the crossing of the threshold. I will call it the cumulated effect.
Remember my earlier overdetermination scenario where police investigators and coroners gathered evidence pointing to the overdetermination of a killing. There is no difference between this scenario compared to a non-overdetermined version of the same scenario in terms of the threshold effect. However, there is in terms of the cumulated effect originating from two sources in one case, but from only one source in the other. There are many ways of reaching the threshold called death, or in other worlds the state when a living being becomes incapable of regaining its homeostatic equilibrium. In cases of overdetermined death much damage is caused to the body, which would have been enough
many times over. The damage done can be approached from the point of view of someone who is only interested in whether the body can still regain its homeostatic equilibrium, and also from the point of view of a coroner who tries to reconstruct how that particular effect came about.
It is important to highlight here that only threshold effects can be overdetermined, but there seems to be no way to overdetermine the cumulated effect produced by overdeterminer causes together. The cumulated effect always goes beyond the threshold effect47. The amount of water that flows over the bowl is determined by the sum of all inflow
and it is impossible to have more or less overflow than what the sum of all inflow minus the volume of the bowl provides.
To sum up, on the one hand, in known overdetermination scenarios there is a threshold effect to attend to, on the other hand in all of these cases, there is also a cumulated effect to consider. Empirically speaking, this is an objective fact concerning such situations: whether we attend to this or that kind of effect does not make any of those effects less real or objective.
47 The crossing of a threshold expresses a change in one discreet property of an object. E.g. that it reached its
melting point and from a solid state it became liquid. But, as the heat transferred was more than necessary for phase transition there is a cumulated effect as well, the exact temperature of the resulting liquid. The difference between the threshold effect and the cumulated effect can probably be expressed in terms of the determinable- determinate distinction. The determinate state of matter would be the cumulated effect of the two causes, while the determinable state (being liquid) would be the threshold effect. In many cases we are only interested in manipulating the determinables, but that does not mean that there are no necessary side-effects to any such manipulation in terms of more determinate descriptions of that property.