Over at Siris Brandon offers some interesting criticism of my argument against substance dualism. He distinguishes two senses in which we may say that a theory is viable. In one sense we simply mean to be asking what reasons someone might have for believing in that kind of thing. In that sense a viable theory is one which there is reason to believe. In another sense we may be asking not what the reasons are to believe it but instead what the thing in question is in the first place. A viable theory in this sense is one that can tell us what the thing is. Brandon then goes on to show that this distinction corresponds to a distinction between things that a problem for a theory and things that a problem within the theory. Brandon then goes on to argue that my complaint is not a problem for the theory that there are immaterial substances but is rather a problem within the theory of immaterial substances itself and so should be answered by more research into immaterial substance and not with a dismissal of the theory.
The picture that Brandon seems to have is this. We decide whether or not there are good theoretical/common sense reasons to believe that there are immaterial substances and if we decide that there are we then try to construct a theory of what they are. Naturally in doing so we do not know very much about the immaterial substances and so one of the projects of the theory is to say more about what they are. Given this it is a mistake to think that our lack of understanding about what immaterial substances are is any reason to think that they don’t exist.
I completely agree with the spirit of Brandon’s comments but I do not agree with his conclusions. First, to where I agree. We clearly must recognize the kind of distinction that Brandon draws. And while I disagree that there are any real reasons or evidence for immaterial substances I agree that if there were, or if one thought there were, one should then go on to try and give a theoretical account of what they are.
Let us be generous and grant that there are reasons to think that some kind of substance dualism is true. When we then ask what an immaterial substance is we get told that it is the immaterial substrate of thinking and consciousness and that it is not located in space-time as we know it. David Chalmers has offered one way of making sense of this in terms of the matrix, and I won’t rehash it here but it seems clear that this kind of move makes the immaterial substance material outside of the matrix and so isn’t really a threat. What else can we do? At this point we have no further ideas. All we can say is that it is an X we know not what which underlies thinking and consciousness. If the theory never progresses past this point then we may start to think that it is in trouble.
So, to take Brandon’s example of evolution in biology, people had proposed accounts that looked evolution-ish as far back as Democritus, who seemed to have proposed that life as we know it was built up over time from simpler parts but this was not the theory of evolution because he did not have the right mechanism (natural selection). If the theory of evolution had stayed at the level of “evolution is whatever it is that underlies speciation and isn’t God doing it” no one would care about it. So too if the best that substance dualism can do is to say that an “immaterial substance is whatever it is that underlies consciousness and thinking and isn’t physical” it seems uninteresting. One might think this shouldn’t be a problem because lots of theories have been like that in the past (gravity seems to be a notable one) but the problem is that it has been this way since its inception and not one step forward has been taken in 3,000 years. The most significant advance, if one were to call it that, has been the post-Humean nonchalance to the issue of physical/non-physical causation. If all there is to causation is constant conjunction, and the non-physical events are constantly conjoined with the physical ones then voila! mind-body problem (dis)solved!!
The upshot then is that fleshing out the theory will ultimately shed some light on the reasons for believing it. If we seem in principle unable to advance in specifying what a immaterial substance is, and we have physicalist alternatives that are relatively well understood, substance dualism starts to look impossible and we seem to loose our reason to believe it, which will in turn cause us to re-evaluate the reasons we used to have for believing it.