I have said that there are four versions of the argument from reason that, taken together, push me toward theism. The first argument establishes the reality of selves, persons, conscious states, and thoughts, while the second argument establishes the reality of free will. These two conclusions point in the direction of a third claim about the reality of mental causes, but the reality of mental causes is also independently supported by another version of the argument from reason.
Mental Causes
First, what do we mean when we talk about any kind of cause? The most straightforward answer is anything that produces an effect, by which I mean some kind of change in the world. I've heard some people say that causation has no role to play in physics. But either the people who say things like this are using the words "causation" and "physics" in very specific, technical senses—in which case, who cares?—or they are actually denying that causation plays any role in reality, in which case I don't see how we can possibly take them seriously. Anyone who says that throwing a baseball through a window plays no causal role in shattering the glass is not even remotely coping with reality. (In fact, if anyone really denies causation altogether, then the argument from reason discussed below will help expose the error in their thinking.)
Second, what do we mean by mental causes? They are distinguished from physical causes. In the physical world, I think we usually talk about events (rather than objects) as causes. For instance, if I throw a baseball through a window and shatter the glass, we can quibble over whether it's more appropriate to say that the baseball caused the breaking of the glass or that my throwing of the baseball caused the breaking of the glass. I have no strong opinion on the matter, at least not for now. But a physical cause is some physical thing or event that brings about some change.
By contrast, a mental cause would involve a mind or some other non-physical thing with causal power. If I have an immaterial mind, and if my mind is able to bring about change in the physical world (say, if I decide to raise my hand), then mental causation is possible.
Now what does this have to do with atheism? Most atheists affirm a view of the world in which there is no mental causation. Why? Because a crucial part of their worldview is the underlying conviction that the physical world—all of physical reality—is causally closed. Everything that happens is the result of prior physical conditions. If the physical world is not causally closed, then there are things that exist that can bring about changes in the physical world even though they are not part of the physical system, and (according to many people) this would potentially undermine science.
On the other hand, classical theism entails the reality of mental causation, since God is an immaterial person who can effect change in the physical world. It is no wonder why theism is usually linked to an affirmation of substance dualism, which holds that there are both mental and physical substances.
As a result, atheists typically either deny that we have minds, or they equate our minds with our brains, or they say that our minds are just mental properties that somehow arise from certain physical conditions and have no causal effect on physical reality. As long as one of these options is correct, we can continue to believe in the causal closure of the physical world. Thus, atheism very often involves a rejection of mental causation.
Free Will and Causal Closure
There is an obvious connection between causal closure and determinism. As discussed in the last post, determinism holds that every event is the inevitable result of prior conditions. The atheistic view of determinism (which I will just call "determinism" here for simplicity) holds that every event is the result of prior physical conditions. This is just another way of saying that physical reality is causally closed. Now, we've already seen why it's self-defeating to affirm determinism, because determinism implies that our beliefs about determinism are determined by prior physical conditions over which we have no control. If our beliefs are determined in this way, then it undermines the rationality of our belief in determinism (see the previous post for a longer discussion). Thus, we have good reason to affirm the libertarian view of free will.
Now, if we have free will in the libertarian sense, as I believe we do, then we have already undermined the causal closure of the physical world, since our free choices cannot be explained in terms of physical causes. This is why libertarian freedom is often (though not always) linked with belief in immaterial minds or souls. Since we have free will, mental causation must be possible.
The Argument from Reason
However, there is an independent argument for the reality of mental causation that makes no reference to the debate over free will and determinism, and I find it to be just as convincing. The argument goes like this:
- If beliefs about an argument’s conclusion are not even partially caused by beliefs about the argument’s premises, then the inference to the conclusion of any argument is not rational.
- If there is no mental causation, then beliefs about an argument’s conclusion are not even partially caused by beliefs about the argument’s premises.
- Therefore, if there is no mental causation, then the inference to the conclusion of any argument is not rational. (1, 2)
- But the inference to the conclusion of at least some arguments is rational. [cannot be rationally denied]
- Therefore, there is mental causation. (3, 4)
- If P, then Q.
- P.
- Therefore, Q.
a is my belief that "If P, then Q."
b is my belief that "P."
c is my belief that "Therefore, Q."
Obviously, we can see that there is a logical connection between the content of these beliefs. But how are these beliefs related to each other in my mind? It is crucial to understand that, if there is no mental causation, then my three beliefs just exist independently of each other, and the only reason each one exists is because of the physical causes that produce the relevant brain states or mental properties. Those physical causes do not have any logical relationship. To see why, consider the following three brain states.
x is the brain state associated with a.
y is the brain state associated with b.
z is the brain state associated with c.
When I say there is no logical relationship between these three brain states, what I mean is that brain state z does not "follow from" brain states x and y. It may not even be caused by the same physical processes that produced x and y. In that case, my belief c just exists because of physical, non-rational causes that are bringing certain changes about in my brain.
This means that my belief in c (or really in the conclusion of any argument) has nothing to do with my beliefs in the premises of that argument. Rather, I hold all of those beliefs because of physical causes, which are not concerned about logical validity. To see why this is a problem, suppose that we change the content of belief c.
c is my belief that "Therefore, R."
We can clearly see that my inference to R is invalid, since it does not follow from the two premises. But what does this have to do with brain states? In a causally closed world, physical causes are going to do what they're going to do. I may think that R follows from the two premises, or I may think that it does not, but neither thought is going to make any difference in how I interact with the physical world. Yet this seems wildly implausible. Surely there must be a meaningful difference between the processes that produce a valid inference and the processes that produce an invalid one, and it makes no sense to explain this difference in terms of physical causes.
In fact, we can make the implausibility more clear if we replace the content of all three of my beliefs.
a is my belief that "If I am standing in the middle of a busy highway, I will probably get hit by a car."
b is my belief that "I am standing in the middle of a busy highway."
c is my belief that "Therefore, I will probably get hit by a car."
Given these beliefs, I will almost certainly try to move myself away from the highway. Yet if there is no mental causation, then the only reason my body moves (or doesn't move) from the highway is that it was caused to move by physical brain states or some other set of physical causes. My beliefs had nothing to do with it. I submit that this is absurd.
I'll end by offering a slightly modified version of the argument, which directly references brain states. This makes it even more clear that mental causes must be able to interfere with the physical world if our beliefs are rational.
- If brain states associated with beliefs about an argument’s conclusion are not even partially caused by beliefs about the argument’s premises, then the inference to the conclusion of any argument is not rational.
- If there is no mental causation, then brain states associated with beliefs about an argument’s conclusion are not even partially caused by beliefs about the argument’s premises.
- Therefore, if there is no mental causation, then the inference to the conclusion of any argument is not rational. (1, 2)
- But the inference to the conclusion of at least some arguments is rational. [cannot be rationally denied]
- Therefore, there is mental causation. (3, 4)