Physical causal closure

This principle could be taken to mean that every good causal story we can tell has to be couched in physical terms or that all causation is always in virtue of physically definable or reducible properties. Taken this way, however, this principle would just beg the question against nonreductive materialism. Under physical causal closure, it is not that we can never invoke physically irreducible higher-level properties as causes for a physical event. We may very well cite some irreducible mental property as the cause of some physical event. The point is that this mental property, if it is to be causal, must somehow be anchored in the physical world. It must be tied to the physical by some sort of supervenience or realization relation. This close tie to the physical will always make it possible, in principle, for us to tell a causal story in terms of physical properties, even though the best causal story might not always refer only to physical properties. Thus, we will never be forced to go outside the physical domain and refer to physically irreducible properties in order to find a sufficient cause for a physical event. So the principle of physical causal closure requires that if we pick any physical event, it will always be possible, in principle, for us to find a purely physical causal chain for that event. So if we take any physical event P, we should be able to find some property or group of properties P, such that P is physical and P is a sufficient cause for P. ... 

In order for the causal closure of the physical domain to, by itself, rule out physically irreducible properties as causal, one would need to hold a much stronger notion of physical causal closure. One would need to hold that the causal closure of the physical domain implies not just that every particular physical event will have a sufficient physical cause, but also that the sufficient physical cause will always exclude any physically irreducible properties as causal. This sufficient cause and any properties reducible to it will be the only causal properties, and there will be no physically irreducible causally relevant properties. On this view, the only causally relevant properties we could find for physical events would be physically reducible properties and the only causal explanations for physical events would refer only to physically reducible properties. Not only do we not need to look outside the physical domain to get a causal story, but looking outside the physical domain will give us no information at all about the causal process. I will refer to this strong view of closure as exclusive closure. Let us now turn to Kim s view of physical causal closure. 

However, Kim makes it clear that he also holds that physical causal closure implies causal and explanatory sufficieney. Immediately after stating the principle of physical causal closure and its explanatory analogue, he says ... 

Thus, Kim seems to think physical causal closure implies not just that we can always fiind... 

Thus far, Kim s view of physical causal closure does not differ at all from the observations I have made about physical causal closure. Physical causal closure requires that if a particular physical event has a cause at t, it will have a sufficient physical cause and sufficient physical causal explanation at t. But does Kim hold a view that is even stronger than this Kim, at one point, suggests the adoption of what he calls strong closure ... 

Thus, except for the brief mention of strong closure here, Kim chooses to rely on his weaker notion of closure - i.e. that closure implies only sufficient, but not exclusive, physical causation - in his arguments against nonreductive materialism. Therefore Kim says that physical causal closure does not by itself exclude nonphysical causes, or causal explanations, of physical events (2005 17). According to Kim, it is only when we adopt the exclusion principle in conjunction with closure that nonphysical causes get excluded (2005 17). So Kim does not seem to rely on a view like strong closure or exclusive closure. Kim seems to hold a more standard view that we can accept for our purposes -i.e., that physical causal closure implies that all particular physical events with causes have sufficient physical causes and sufficient physical causal explanations. 

Thus, Kim cannot and does not assume or argue that closure at L by /Y e/fimplies exclusive closure at L. However, Kim does seem to hold that closure at a level implies the irreducibility of that level. Although Kim s view of physical causal closure seems fairly standard and acceptable for our purposes, we need to ask whether his view of closure at L is a good one and whether Kim can succeed against Block s drainage worries with this view of closure at L. 

Physical causal closure For any physical event P and any time t, if a cause ofP occurs at t, then at least one physical event P occurs at t that is a sufficient cause ofP a cause of P that determines its objective probability. 

Thus, by the exclusion principle, we are forced to rule out either M or P as the cause of P. And since we know, by the causal closure of the physical, that P has a sufficient physical cause P, there is no question as to whether P should be taken as a cause of P. ... 

First, it is important to note that Kim s view is utterly committed to the causal closure of the physical domain. Kim has stated many times that he believes in the causal closure of the physical domain. Yet it seems that in addition to merely asserting this belief, Kim s entire theory requires that there be some lowest closed level (or closed union of levels). First of all, Kim seems to think that a bottom closed level is required in order to make the exclusion argument even work (if it does work). I have raised my... 

Kim clearly believes in the closure of physics and his view of causation seems to require the closure of physics. But the question we ought to ask is What if physics isn t actually closed There are good reasons to believe in the causal closure of the physical domain. But surely it is an empirical question whether physics is actually closed. And... 

The view of causation I am advocating can be agnostic about whether physics is causally closed. Because my view doesn t require that all causation be sufficient causation, my view will not require that there be some closed level with sufficient causation to ground all other causation. On a nonreductivist view of higher-level causation, we can have irreducible causal properties that don t have to be grounded in sufficient causation at some lower level. For the purposes of discussion, I will play along with Kim and assume that physics is causally closed. However, my view is not committed to the causal closure of physics and therefore is not undermined by the empirical possibility that physics might not be closed. Now, let us look more closely at Kim s view of closure. 

The notions of the causal closiue of the physical domain and the causal closure of specific levels of organization are central to both Kim s exclusion argument and his response to generalization worries. The idea of causal closure of the physical domain is... 

This is not to say, however, that we cannot go outside the physical domain and refer to physically irreducible properties as causes or as part of our causal explanation for a physical event. The fact that we have sufficient physical causation or causal explanation does not by itself rule out physically irreducible properties as causes. Thus, we need to be careful to separate the notion of sufficiency from the notion of exclusiveness. The causal closure of the physical implies that physical events with causes will have sufficient physical causes and sufficient physical causal explanations. It does not imply, however, that this sufficient physical cause will exclude all physically irreducible properties from being causal. And it does not imply that we can never refer to physically irreducible properties when giving a causal explanation for a physical event. 

When I discuss causal closure, I will often, for brevity, leave implicit two notions. First, what I say will refer to events if they have causes. So if I say, for example, closure implies that every physical event has a physical cause , I mean that if an event has a cause, it has a physical cause. This leaves open the possibility that there could be an event that did not have a cause. Similarly, with causal explanations, I mean that if an event has a causal explanation, then such and such is true about that causal explanation (see Kim 2005 16, note 8). Second, when I refer to causes, I am speaking of causes that occur at time t. So if I say, for example, every physical event has a physical cause , I mean that if an event has a cause that occurs at time t, it has a physical cause that occurs at time t. This is to rule out the possibility of the physical cause being merely a distal cause that, say, caused a nonphysical event, which then in turn caused the physical event in... 

The causal closure of the physical domain only implies that it is not necessary to refer to physically irreducible properties as causes. There will always exist a sufficient physical cause and sufficient physical causal explanation for any particular physical event that has a cause, but that does not imply that physically reducible properties are the only ones that can be causal or that physically irreducible properties must be excluded as causes. 

The causal closure of the physical domain. If a physical event has a cause at t. 

This closure principle and its explanatory analogue are quite weak. All they state is that any physical event that has a cause at a given time will have a physical cause at that time, and that any physical event that has a causal explanation at a time will have a physical causal explanation at that time. As stated, they do not require that this physical cause is a sufficient cause or the exclusive cause, nor do they require that the causal explanation will be a sufficient causal explanation or that it will exclude other causal explanations. 

So, here s the exclusion argument itself Suppose that some M-instantiation causes an TVf-instantiation. By supervenience, we know that the -instantiation has a physical supervenience base, But P -instantiation is nomologicaUy sufficient for AP-instantiation. It therefore appears that Af and P each have a claim to being responsible for the instantiation of Af on this occasion, and the two claims appear to be in tension with each other. The only plausible way to resolve this tension is to conclude that the Af-instantiation causes the AP-instantiation by causing a P-instantiation. But, again by supervenience, Afhas a supervenience base, P. By the causal closure of the physical, the P-instantiation must have a complete physical cause — presumably, the P-instantiation. But now P and M are in direct competition for being the cause of the P-instantiation. ... 

Davidson s anomalous monism is usually thought of as a version of nonreductive physicalism. But its commitment to physicalism may be rather weak because, though Davidson does endorse the causal closure of physics, it is not clear that he agrees with the supervenience claim I call Jackson-Lewis physicalism since he denies that there are tight connections between the mental and the physical. 

The first two claims characterize a physicalist worldview, or what I call physicalism. Condition (r) expresses the physicalist idea that all God needed to do to make the universe is to distribute the fundamental physical properties in space and time and make the laws of fundamental physics. All facts about macroscopic objects, their colors and behaviors, and facts about people, their thoughts and experiences, and truths about causation and the special sciences, and so on are metaphysically entailed by the fundamental physical facts and laws. Condition (2) says that the physical laws are closed and complete in the sense that, given the complete fundamental physical state at t and the laws, whether or not E occurs at t, or its chance of occurring, is completely determined. 1 assume that whatever causation is, condition (2) implies the casual completeness of physics in that E t ) s physical causes at t are sufficient to determine its occurrence (or the chances of its occurrence). Condition (2) is a consequence of (r), and it is possible to derive (r) from (2) and some other plausible premises, but I separate them since nomological and causal closure will figure importantly in our discussion. ... 

Kim (1998b) has defended a bold position concerning mental causation the nature of our world is such that every mental event is either a physical event or an epiphenomenon. One of the main principles he relies on in making his case is the causal closure of the physical, arguably a presupposition of physical theory. That principle has been formulated in various ways. I will formulate it as follows ... 

Insofar as Hendry s theory of emergence focuses on entities, it is at odds not only with reductionism, but also with the causal closure or completeness of physics - the thesis that all physical events are determined (or have their chances determined) entirely by prior physical events according to physical laws (Papineau 1990, p. 67). This is because on Hendry s view, molecules are capable of downward causation. So if the theory of emergence advocated by Hendry is true, the set of physical causes must be supplemented with sui generis chemical causes - molecules exerting downward causation on their parts. 

By the exclusion principle, we are forced to rule out either the mental property or the physical property as causing the behavior. If we assume closure, then we already know that the behavior has a physical cause, so we cannot rule out the physical property as causal. Thus, we are forced to rule out the mental property as a cause. All the causal work has already been done by the physical property, and there is simply no causal work left for the mental property to do. So, the suggestion goes, the irreducibility of mental properties to physical properties will lead to the causal impotence of mental properties. 

We expect the physical world to be causally self-contained and explanatorily self-sufficient. That is, we suppose that if a neural event - or more broadly, a physical event - has a cause, or an explanation, then it must have a physical cause and a physical explanation. This is the principle of causal/explanatory closure of the physical domain (2005 154). 

Now notice here that Kim refers to events and not properties in his statement of strong closure. If Kim were really just talking about events here, then strong closure would be completely uncontroversial and rmproblematic for any materialist. Nonreductive materialists could hold on to a Davidsonian anomalous monism, and hold that all causes of physical events are themselves physical events. This would still leave open the possibility that these physical events could have physically irreducible properties that are sometimes causally potent. 

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