One can be a substance dualist in the philosophy of mind without being an interactionist. And one can be an interactionist without being a substance dualist. (Exercise for the reader: explain why both assertions are true.)
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But suppose you are a latter-day Cartesian: you are both a substance dualist and an interactionist: you believe that mind and body are distinct (kinds of) substances and you also believe that some mental events cause physical events and some physical events cause mental events. You will be taxed by some with a supposedly insurmountable difficulty: how can there be mind-body and body-mind causation if mind and body are radically different kinds of substance?
There are benighted souls who think this objection is decisive against Cartesian dualism. They are mistaken.
To show that the objection is not decisive it suffices to set forth a theory of causation that would allow mental events to cause physical events (and vice versa) even if a mental event is construed as an irreducibly mental substance's instantiation at a time of a mental property and a physical event is construed as an irreducibly physical substance's instantiation at a time of a physical property.
Well, a regularity theory of causation would do the trick, would it not? Suppose we say that:
Event-token e1 causes event-token e2 if and only if (i) e1 temporally precedes e2, and (ii) e1 and e2 are tokens of event-types E1 and E2 respectively such that every tokening of E1 is followed by a tokening of E2.
On this Hume-inspired theory (sans the contiguity condition), causation is just regular succession. If this is the correct theory of causation, then there is nothing problematic about mental events causing physical events, and vice versa.
Of course, if you think that causation must involve the transfer of some physical quantity such as energy or momentum, then of course substance-dualist interactionism is out. But there is nothing in the very idea of substance-dualist interactionism to render it incoherent. It all depends on how causation is understood.
Suppose one adopted a counterfactual analysis along the lines of: c causes e =df had c not occurred, e would not have occurred. There is nothing here to rule out substance-dualist interactionism.
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I think your approach to solving the mind body interactionism problem has a few problems. I am a latter day Cartesian and I am in complete agreement with you that the traditional objection to dualism is not even close to being a defeater, to use Plantinga’s jargon. A regularity theory of causation is a theory of causation, but does it correspond to what we experience? Why must we avoid direct causation of physical events by mental events? I have never read or heard anything to convince me that we should avoid it. My mind causes something to happen in my brain when I talk, walk, or make a funny face at my daughter. Obviously, we are not able to directly perceive this aspect of our minds; the precise details are unknown. Husserl might say it is ontologically immanent and epistemologically transcendent. If you or anyone else has made a discovery to the contrary, please let me know! I would suggest that the kinship of mind and matter is much closer than is often thought. In a personal interview with him, I found that Dallas Willard solves the problem in this way, “Mind is an energy that does not have to traverse space to have its effects.” Interesting statement to say the least. It implies direct causation of physical events by mental events. I think the theory of causation is important here, but the real problem is a metaphysic that excessively limits what mind energy can do. We make the mind like a ghostly entity which passes through material objects and only occasionally directly effects them. The statement above may be compatible with regularity causation, but it is also compatible with direct efficient mental causation of physical events. That is where I stand today.
Posted by: Sam | Saturday, 30 July 2005 at 16:38