The mind-body problem can be seen as arising from a set of three propositions, which together form an inconsistent triad. Each leg of the triad has some support, so to resolve the problem posed by this set of propositions it is necessary to reject one of the propositions, probably by arguing that it has weaker support than the other two, or that somehow they aren’t really in contradiction, contrary to appearances. The propositions themselves are as follows:
1: Mental and physical events / properties are distinct
This proposition is supported primarily by our intuitions about the nature of the mental and the physical. Intuitively the physical is characterized by facts about location and extension and the physical laws that physical objects obey. In contrast mental events seem distinct from these facts, and have properties, such as being intentionally direct at (about) objects, which physical events don’t have. We might also argue that the lack of a theory connecting the mental events to physical events is further evidence that there is no such connection, reasoning that if the mental events really were identical to certain physical events then we would have discovered how and why by now. Rejecting this proposition is the solution advocated by Hobbes and the materialists who followed him.
2: Mental and physical events interact, such that mental events explain certain physical events, and vice versa
This proposition is supported by our intuitions about perception and action. Certainly it seems like when we perceive objects the physical world is having an effect on our mental events. And, conversely, when we make a choice to take some action it certainly seems like our will is the cause of our action. Furthermore, the hypothesis that there is a causal connection between mental and physical events allows for certain explanation of behavior that are, as far as we can tell, good explanations. For example, we might explain why someone drove to the store in terms of their desire to buy groceries. All the evidence we can gather points to this being the correct explanation. If we ask this person why they went to the store they will tell us that it is because they desired to buy groceries. And if, in similar situations, we buy groceries for them they will not go to the store, which supports the idea that it was their desire that caused them to go to the store, because by eliminating their desire we seem to prevent them from going to the store. Rejecting this proposition is the solution advocated by Leibniz and Spinoza and the epiphenomenalists who followed them.
3: The causes of a physical event are all physical
This proposition is supported by our scientific investigations. Science can seemingly explain everything that occurs, or at least nearly everything. And its explanations never involve mental events that causally influence the outcome. And the things that science can’t explain yet aren’t really the kinds of things that make sense to attribute to the effects of the mind (dark matter, ect). In addition to this to say that the mental is the cause of something physical might be to automatically deny proposition 1. This is because of causal locality, which says that at the time of the effect the cause and the object being affected are co-located. Given that, if mental events could have an effect on physical events then mental events would have a location, determined by where the physical event that they had an effect on was when they had an effect on it. And if we give them a location then we are denying that mental and physical events are really different kinds of thing, and instead we would seem to be making mental events simply an additional kind of physical event. Rejecting this proposition is the solution advocated by Descartes. Unlike the others rejecting this proposition doesn’t have a modern tradition associated with it, although property dualists occasionally say things that sound like they might be advocating rejecting this proposition. And on a regular basis someone tries to show how quantum physics allows the mind to have an influence on physical events, but inevitably they are shown to be misinterpreting quantum mechanics.
Of the three propositions number 1 seems obviously the weakest to me. Its support comes only from our intuitions, which are known to be fallible, and from the fact that we don’t have an explanation of the mental in terms of the physical yet, which does not conclusively show that such an explanation is impossible. It is much harder to reject 2 or 3. 2 is associated with psychology and cognitive science and 3 is associated with physics. To deny 2 or 3 is to claim that one of these disciplines is significantly in error. Since neither psychology or physics seems to be so substantially flawed rejecting 2 or 3 thus seems impossible, or at least a less desirable than abandoning our intuition that the physical and mental are distinct.
Certainly that is the resolution that this problem seems to suggest. But to show that rejecting proposition 1 is really necessary we must also show that it isn’t possible to accept all of them. One possible way to try to reconcile all three propositions is through an idea called “aspect dualism”, which holds that the mental and the physical are simply different expressions of the same ultimate reality. The problem with this solution though is that it is still a rejection of proposition 1, because it claims that ultimately the mental and the physical are ways of describing the same thing. It also fails to provide an explanation of what the ultimate reality is. Why not just accept that they physical world is the ultimate reality, and that the mental properties are simply a way of looking at that reality which is radically different from the way we perceive it through our customary senses; in other words, why not simply be materialists?
A better response is to try to separate explanatory power from causal power. Specifically what is needed is a way for mental events to explain physical events without causing physical events. However it is not easy to see how this can be done. If they are explanations only by convention, meaning that the mental and the physical don’t interact, but we take the mental as explaining some physical events simply because we are used to the mental events preceding certain physical events, then we are saying that are explanations are basically mistaken, that the mental isn’t the reason the physical events went as they did, which is to reject proposition 2. If the mental is to be a valid explanation of the physical then there must be a reason that given that mental event the physical events couldn’t have possibly turned out differently. But this requires some kind of causal interaction, which is to deny proposition 3. So while this proposal seems promising it too is flawed.
Thus, since we can’t reconcile all three propositions it seems like we are justified in rejecting proposition 1.
[This post is adapted from, and builds on, part of a lecture by professor Jolley.]