What it is to be persuaded by an argument

This is from my reply to Keith Parsons in essay "Some Supernatural Reasons Why My Critics are Wrong" (a title that was given to my essay by someone else), in Philosophia Christi (Volume 5, no. 1, 2003).

But think for a moment about what it is to be persuaded by an argument. If we are thinking in common-sense terms, we would have to say that what goes on when we are persuaded by Parsons's argument that Arizona State will not be in the BCS this year is that we consider the epistemic strength of the premises, the grounding relation between the premises and the conclusion, and then accept the conclusion as a result of considering the evidence presented in the argument. To be convinced by an argument is for the reasons presented in the argument to play a causal role in the production of the belief. If the argument is causally irrelevant to the belief, then we cannot say that the argument was persuasive. This can often be cashed out counterfactually: If I really am persuaded by Parsons's argument, then it cannot be the case that I am such a partisan of the Arizona Wildcats that I would think the worst of the Sun Devils' prospects even if the Sun Devils had a Heisman trophy candidate at quarterback, outstanding and experienced running backs and wide receivers, a rock-solid offensive line, and was returning everyone from what had been the stingiest defense in the Pac-10 the previous year.

On the one hand, the reasons have to persuade me in virtue of their being reasons. The logical force of the argument has to have a causal impact on belief. It has to make a difference as to whether I form the belief or fail to form the belief in question. And that, by the way, is bound to make a difference as to what I do with my body. I am going to behave differently if I think the Devils have a good chance to take the Pac-10 title than if I don't. And that is going to affect what the particles in the physical world do. But if the physical is causally closed, that means that the physical and only the physical can affect where the particles in the physical world go, and, the physical is defined as lacking, at the basic level of analysis, the central features of the mental. So the only way this kind of causal relation could possibly exist, would be if we could analyze the mental in physical terms as a kind of macro-state of the physical. Just as the word "planet" is absent from physical vocabulary, but a whole bunch of particle-states add up to there being a planet, perhaps "S's belief that P" can be added up from a set of physical states. But that seems to me to be just impossible. Add up the physical all you like, and you aren't going to get "S's belief that P." The physical leaves the mental indeterminate. Yet, if science is to be possible, is has to be determinate whether, for example, Einstein is plussing or quussing when he is adding numbers in the course of developing his theory.

So, I argue that you need mental causation for the possibility of science, but you can't get that without affirming what seems to be an implausible reductionism, that conflicts with the indeterminacy of the physical.