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The Causal Closure of the Physical as a Problem for Dualism
Glenn Mason-Riseborough (14/9/1998)
1.0 Introduction
Causal closure of the physical world is a strong argument against some forms of dualism. This essay will discuss the problem of the causal closure of the physical world and the forms of dualism that are affected by it. The initial task of this essay will be to examine dualism in its various forms with respect to causal interactions. I will then discuss what it means to say that the world is causally closed and the evidence for and against this view. This will include examples that are often used as evidence against the claim, and the responses that science gives. Finally, I will examine which forms of dualism are affected and why, and hence which view deals best with the problem. It is not within the scope of this essay to discuss other potential problems of dualism aside from the problem of causal closure of the physical world.
2.0 Dualism
As initial background, it is necessary to point out that dualism is the doctrine that asserts that the world is made up of two types of matter. For no other reason than convenience, we will call these two types physical and mental. A dualist states that there is certain “stuff” that cannot be accounted for purely by the physical sciences. This may include events such as thoughts, feelings, beliefs, and desires. Dualism is usually contrasted with monism, which asserts that there is only one type of “stuff.” We may further identify different types of dualism based on the causal interactions between the physical and mental. Braddon-Mitchell and Jackson (1996) identify three main types of dualism using this criterion – parallelism, epiphenomenalism, and interactionism. It is also logically possible to identify a fourth type; I shall call it reverse-epiphenomenalism (see Figure 1). These four types may subscribe to either substance dualism or attribute dualism. Substance dualists maintain that although our bodies are fully described by the physical sciences, events such as thoughts and feelings takes place in some purely mental substance (eg soul, spirit etc). On the other hand, attribute dualists subscribe to the belief that while there is no mental substance, mental life is a non-physical attribute of sufficiently complex physical structures. In the context of this essay this distinction between substance and attribute dualism is largely unimportant, I will use the terms substance and attribute interchangeably.
2.1 Parallelism
Parallelism is perhaps the simplest form of dualism. This account states that there are no causal paths between the physical and the mental. The physical does not effect the mental and the mental does not effect the physical. These two substances/attributes co-exist in synchronicity such that it appears that beliefs and desires are affected by physical events and vice versa. However, according to this view the appearance is merely the illusion of correlation – there are no causal interactions. Braddon-Mitchell and Jackson (1996) place very little emphasis on this form of dualism, writing it off as implausible and stating that they are unaware of any current parallelists. This is no doubt because epiphenomenalism seems more intuitively true in its acceptance of the physical effecting the mental.
2.2 Epiphenomenalism
In this form of dualism, the causal link is unidirectional. The physical can effect the mental but the mental cannot effect the physical. Like a parallelist, an epiphenomenalist is forced to admit that his/her beliefs and desires do not effect his/her physical actions. However, unlike a parallelist, an epiphenomenalist is prepared to admit that the physical world can effect his/her beliefs and desires.
2.3 Reverse-Epiphenomenalism
It is logically possible for the unidirectional causal interaction of epiphenomenalism to be reversed. Thus, a reverse-epiphenomenalist admits that his/her beliefs and desires do effect his/her physical actions, but the physical world does not effect his/her beliefs and desires. A reverse-epiphenomenalist is forced to accept that the physical world is not causally closed. Realistically speaking, this is not a strong position to hold because, like parallelism, it states that the physical does not effect the mental, while additionally having to contend directly with the problem of the causal closure of the physical world.
2.4 Interactionism
Historically, this is perhaps the most common form of dualism. This view states that the causal interaction between the physical and mental is bidirectional. In other words, our beliefs and desires do effect our physical actions and our physical actions do effect our beliefs and desires. Like an epiphenomenalist, an interactionist accepts that the physical world can effect his/her beliefs and desires. Like a reverse-epiphenomenalist, an interactionist is forced to accept that the physical world is not causally closed.
3.0 Causal Closure of the
Physical World
To say that the physical world is causally closed is to say that all physical actions have a purely physical aetiology. Conversely, those (like reverse-epiphenomenalists or interactionists) who say that the physical world is not causally closed, maintain that there are physical events that are not fully explained by the physical sciences. In the widest possible sense, we can see science as a research project that attempts to discover whether or not the physical world is causally closed. If at any time science discovers some event that cannot be accounted for by purely physical aetiology, then we are forced to admit that the physical world is not causally closed. Interactionist dualists often make claims about events that cannot be explained by science, these days these events are often termed paranormal or miracles. Science will often attempt to “debunk” these events, either directly or indirectly. Due to space constraints I cannot cover all such claims of the paranormal, so I will restrict this to one of the more popular and spectacular claims against causal closure – fire-walking.
3.1 Fire-walking
Fire-walking is an impressive ritualistic event in which a person walks over red-hot coals (or other materials) as evidence of their (or their god’s) non-physical control over the physical world. It has a long history, especially in Asian countries as a religious ceremony of devotion. In the context if this essay, it may be used as evidence of “mind-over-matter.” The specifics of the activities surrounding the event of fire-walking may differ between cultures, but commonly this time is used to “cleanse” the fire-walker of impurities. This may include abstinence from sex for one month, a vegetarian diet for one to three months, making vows, meditating, and after the fire-walk the feet may need to be washed with milk. If these activities are not performed correctly, the fire-walker will suffer extreme burns; if the activities are performed correctly, the fire-walker will not be affected by the extreme heat.
Walker (1988) explains the physics of fire-walking in an essay on the Leidenfrost effect. It is important to point out that none of the rituals described above are necessary components of fire-walking, they are all superstitious behaviours. There are two main factors to consider for the successful completion of a fire-walk. Firstly, coals are not good conductors of heat. Even though it may be extremely hot underneath, the coals themselves contain very little energy. A moderate paced walk is good enough to allow insufficient time to elapse before the heat burns the feet of the fire-walker. Secondly, the Leidenfrost effect is a factor. The Leidenfrost effect occurs when a drop of water is placed on a surface of sufficiently high temperature (the Leidenfrost point of water is around 200°C). The water beads up and rests on a thin (0.1 – 0.2 mm) layer of water vapour. This layer of water vapour protects and supports the water, causing the water drop to last significantly longer than it would have at a lower temperature (approximately one minute as opposed to a few seconds). If the fire-walker walks across wet grass prior to the fire-walk, or is sufficiently nervous to have sweaty feet, then this thin layer of liquid protects his/her feet by vaporising as per the description above. Thus, science is able to fully explain fire-walking without the necessity of developing a theory based on non-physical causes.
3.2 Probabilistic
interference by the mental on the physical
A cumulation of scientific evidence shows us that gross physical events always seem to have physical causes. In other words, determinism gives no evidence for the non-causal closure of the physical world. But a non-causal closure supporter may point out that the mental may effect the physical probabilistically. He/she may point out that the mind “chooses” between events at a probabilistic level, and over a period of time the mental creates a skewing that the physical sciences cannot account for. Evidence for this may come from ESP or prophecies for example. Believers will assert that some psychics are correct more often than chance would normally dictate. Again it is not in the scope of this essay to examine every such claim. It is sufficient to state that whenever experiments for this are performed in laboratories, there is no statistical significance to support such claims once other effects are taken into account. Of course, this is a very controversial area, popularly abound with “conspiracy theories,” “cover-ups” and so forth. However, I assume that human nature being what it is, we would very quickly hear about any such scientific evidence against the causal closure of the physical world if it existed. In fairness to psychics (for want of a better word) we may suggest that laboratory experiments are not ecologically valid. That is to say, because of their artificial nature, they do not measure what they set out to measure. Although this is a problem for laboratory experiments, we have no solid evidence for non-causal closure either inside or outside the laboratory. Braddon-Mitchell and Jackson (1996) rightly point out that the sciences have been extremely successful in discovering physical causes for physical events. Of course it would be naive to think that science has currently got all the answers, but we have enough answers to question the need for non-physical causes for physical events.
3.3 Other responses to
causal closure
Braddon-Mitchell and Jackson (1996) point out that there have been attempts to overcome the problem of causal closure by (a) distinguishing between actions and behaviours and (b) appealing to overdeterminism. Due to space constraints, I will not discuss these in any depth, except to state that Braddon-Mitchell and Jackson (1996) do not consider these good enough to overcome the problem.
4.0 Types of
dualism that are affected by causal closure
If we accept the soundness of the causal closure of the physical world, we must then examine how this effects dualism both as a whole and in its various types. Causal closure denies the possibility that the mental effects the physical in any way. Thus, returning to Figure 1 we must eliminate any form of dualism that has a causal arrow from the mental to the physical. This includes reverse-epiphenomenalism and interactionism. The types of dualism that are not affected in this way are parallelism and epiphenomenalism. Thus, by accepting the causal closure of the physical world, while not denying dualism entirely, we are forced to deny interactionism, perhaps the most historically popular form of dualism. Hence, parallelism and epiphenomenalism deal best with the problem of the causal closure of the physical world (but are fraught with other problems). However, causal closure (with the aid of Occams razor) forces us to doubt the necessity of dualism as a whole. We seem to have a complete picture of the world without the necessity of referring to non-physical substances or attributes.
5.0 Conclusions
Dualism, as a doctrine that states that there are two types of matter in the world, can be further subdivided into categories with respect to the way in which the different types of matter causally interact. This essay defined and discussed the categories of dualism referred to as parallelism, epiphenomenalism, reverse-epiphenomenalism, and interactionism. While it is accepted that we do not yet have sufficient evidence to confirm without a doubt that the physical world is causally closed, science has made enough progress to strongly doubt the alternative. We are in a position now more than ever to refute some forms of dualism (reverse-epiphenomenalism and interactionism) and strongly doubt dualism as a whole. This essay showed that while parallelism and epiphenomenalism are not ruled out completely by the causal closure of the physical world (unlike reverse-epiphenomenalism and interactionism), they seem to add more than is required to the physicalist’s (monist) picture of the world.
Bibliography
Braddon-Mitchell, D. & Jackson, F. (1996). Philosophy of mind and cognition. Cambridge, Massachusetts: Blackwell.
Walker, J. (1988). Boiling and the Leidenfrost effect. In D. Halliday & R. Resnick. Fundamentals of physics (extended 3rd ed.). New York: Wiley.