- Problems for Naturalism
- Why Mental States are Causally Irrelevant on Naturalism
Why Mental States are Causally Irrelevant on Naturalism
To define some terms, “logically impossible” means impossible by virtue of self-contradiction, so anything that’s not self-contradictory is logically possible. For example, a magical unicorn is logically possible, but a married bachelor isn’t. “Naturalism” is the denial of the supernatural, such that a “naturalistic universe” is a universe where naturalism is true. A “mental state association set” is a set of associations where certain physical items (such as brains) have certain mental states associated with them.
Suppose we define a “physical state” as the universe’s physical conditions and the laws that govern it at some particular time. The naturalistic mental states (NMS) theorem, which the EAAN paper proves in section 2.2, effectively says that given any physical state for a logically possible naturalistic universe, no matter which logically possible mental state association set would obtain for that state, the universe’s outcome would still be the same. Thus, mental states are a causally irrelevant and useless byproduct of physical processes in the sense that no matter which mental state association would obtain for the physical world at a given time, it would not alter the universe’s resulting outcome.
Although the scholarly EAAN paper gets pretty technical (using math and formal logic) in arguing for mental states being causally irrelevant using something called the naturalistic mental states theorem (proven in the paper), the gist of why mental states are causally irrelevant on naturalism is actually pretty simple. Say that initial physical conditions are the initial conditions as specified in the domain of physics (types of particles, number of particles, their arrangement, etc.), that laws describe how the physical stuff (in the domain of physics) behaves in the absence of supernatural intervention including specifying the physical outcome of what will happen (e.g. where certain particles end up) given certain initial physical conditions in the absence of supernatural intervention, and that a physical state is the initial physical conditions and the laws that govern them.
Insofar as chemistry is reducible to physics (in that chemistry describes how certain combinations of the entities in physics behave with each other; e.g. how molecules interact with other molecules) the laws will consequently include the laws of chemistry. Insofar as biological systems like amoebas are merely very complex combinations of the entities of physics including molecules, those biological systems will include systems of chemistry and physics.
Now consider the following thought experiment: suppose on naturalism a given physical state (one that consisted of one person or many persons in the universe) were to have an entirely different set of mental states associated with this same physical state. Would the outcome be any different? It would not, because the same physical state means the same initial physical conditions and the same laws, so by definition we would get the same physical outcome in the absence of any supernatural intervention to change how things would go. On naturalism, if a different mental state (or no mental states) were associated with a given physical state, we’d get the same physical outcome (e.g. the same behavior) and on naturalism mental states are causally irrelevant in the sense that it doesn’t matter which mental state (if any) is associated with a given physical state; we’d still get the same physical outcome. We can structure this reasoning with the following argument:
- On naturalism, the following is true: If a physical state had any different set of mental states associated with it, the same outcome in the physical world (e.g. one’s behavior) would result.
- If (1) is true, then mental states are causally irrelevant on naturalism.
- Therefore (On naturalism), mental states are causally irrelevant.
Justification for (2): By “mental states are causally irrelevant” I mean in the sense that in the sense that it doesn’t matter which mental states the physical processes generate, and it doesn’t matter which set of mental states (even an empty set) is associated with the physical state of the world: it wouldn’t change the physical outcome (e.g. the same behavior would result). So essentially (2) is true by definition by what I mean by “mental states are causally irrelevant.” (One could mean something different by the phrase “mental states are causally irrelevant,” but this is what I mean by it.)
I suspect this sort of argument would convince most people, but some people (probably naturalists) can be remarkably resistant to the idea that mental states are causally irrelevant on naturalism in the sense that I described, and for such people the scholarly EAAN paper helps with via a rigorously proven theorem.
On naturalism, mental states are causally irrelevant in the sense that which mental states are associated with the physical states wouldn’t affect the outcome. The NMS theorem effectively says that given any physical state for a logically possible naturalistic universe, no matter which logically possible mental state association set would obtain for that state, the universe’s outcome would still be the same. This sort of causal irrelevancy poses (at least) two problems for naturalism. On naturalism, the mental content of a brain state (i.e. the mental state that’s associated with the brain state) doesn’t have anything to do with why its causal behavior is the way it is, whereas common sense suggests a mind’s mental content does have something to do with why it causes stuff. Another problem is that mental states being causally irrelevant in the way I suggested leads to Pr(R|N&E) being low (the Probability Thesis of the EAAN). It seems to me then that mental states being causally irrelevant on naturalism poses a serious problem to naturalism.
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 What if the outcome is random, such that (for example) there is exactly a 50% chance of a certain particle undergoing radioactive decay within a specified time period? In that case, the “outcome” would be something like “there is a 50% random chance that the particle undergoing radioactive decay within that time period such that on average, it will (randomly) decay 50% of the time.”