Sunday, December 20, 2020

Physicalism, epiphenomenalism, and rationality

Physicalism is the view that as humans, all we are is physical stuff. Everything about us can be reduced to some physical state or process. That includes our mental life.

Epiphenomenalism is the view that the physical can give rise to the mental, but the direction of causation cannot go in the other direction. Mental states or processes cannot bring about or give rise to physical states.

Physicalism entail epiphenomenalism. If you can account for every event in your brain by appeal to the physical properties of your brain without any reference to mental properties, then there is nothing for mental properties to do.

Physical properties are entirely objective and third person. Mental properties are entirely subjective and first person. A third person property cannot be the same thing as a first person property. According to the indiscernibility of identicals, if A and B are the same thing, then whatever property A has, B also has, and vice versa. So if there is anything true about A that is not true about B, or vice versa, then A and B cannot be the same thing. So third person properties cannot be first person properties.

Since the physical activity in our brains can be exhaustively explained in terms of their third person properties, that means there is nothing for the first person properties to do. The third person properties can give rise to first person properties, but those first person properties cannot turn around and have causal influence over the third person properties.

Third person properties can be observed or measured by outsiders. But it is impossible to observe a first person property unless you are the person experiencing it. So, for example, you can apprehend your thoughts directly through introspection, but the best a brain scientist can do is look at your neurons. So if your first person properties actually do have causal influence over your brain, then there would have to be causes happening in your brain that were invisible to the neuroscientist. No amount of looking in your brain can reveal a first person property since only third person properties can be observed by third persons. But if physicalism is true, then all of the causes for any event in your brain would have to be third person causes. The neuroscientist could, in principle, observe all the physical states in your brain and apply the laws of physics to figure out what's going to happen next, and he should be able to do this without any reference to first person properties. That means that if physicalism is true, then epiphenomenalism is true.

There is a serious problem with affirming epiphenomenalism. If you deny that your conscious states affect your behavior, then you cannot appeal to evolution to explain how your cognitive faculties became reliable at producing true beliefs. You might be tempted to say that natural selection favored true beliefs over false beliefs, but if our beliefs don't affect our behavior, then our beliefs are irrelevant to natural selection. So natural selection would have no way to select for reliable belief-producing faculties.

With that being the case, the chances that our belief-producing faculties would be reliable is very small. It would be an unimaginable stroke of luck if they happened to be reliable.

If our belief-producing cognitive faculties are unreliable, then you cannot trust them to tell you that epiphenomenalism is true. So affirming epiphenomenalism undermines its own rational basis. So it's a self-defeating belief. And that means it's an irrational position to hold.

If physicalism entails epiphenomenalism, and if epiphenomenalism is an irrational belief, then to be rational, we must reject physicalism.

But let me take this a step further. Let's say that your beliefs somehow could affect your behavior, even if physicalism is true. If that were the case, then there would still be a problem. The problem is that your mental states could only give rise to your behavior by virtue of their underlying physical causes. If you want to equate the physical states of your brain somehow with your mental states, that would be fine under this scenario, but it wouldn't solve the problem. The reason is because although your mental states would, in that case, have causal influence over your brain states, they wouldn't do so by virtue of their semantic content, but by virtue of their underlying physical properties.

Let's say, for example, that there's some physical state of your brain let's call XYZ. As long as XYZ happens in your brain, then you will have a corresponding desire to drink a Dr. Pepper. So XYZ entails a thought that has intentionality. It's about Dr. Pepper and your desire to have it. But as far as your behavior is concerned, it doesn't matter what your thought is about. All that matters is that it has the necessary physical structure to cause you to drink Dr. Pepper.

Consider a philosophical zombie. A philosophical zombie is a human being that has all the exact same physical manifestations of an ordinary human except that there's nobody behind the wheel. If physicalism were true, then philosophical zombies would be conceivable. That means a philosophical zombie would have brain state XYZ, which would result in drinking Dr. Pepper, but there would be no desire, belief, or conscious state behind it whatsoever.

If XYZ fully explains the behavior of a person by virtue of its physical properties, then that behavior would be exactly the same whether XYZ gave rise to mental states or not. You might say that consciousness is the inevitable consequence of XYZ, and that may be true, but it doesn't matter. The thought experiment doesn't depend on whether mental states are the necessary consequence of physical states. It's only meant to illustrate why, under physicalism, the semantic content of mental states are superfluous.

So even if you deny epiphenomenalism by saying mental state can cause physical states in the brain, and therefore behavior, you would still be stuck with semantic epiphenomenalism--the view that mental states cannot have causal influence by virtue of their semantic content, i.e. what those mental states are about, but only by virtue of their underlying physical properties.

And that leaves you with the same problem. If it doesn't matter what your beliefs are about, as far as behavior is concerned, then it doesn't matter whether your beliefs are true, as far as behavior is concerned. And if it doesn't matter whether your beliefs are true, as far as behavior is concerned, then there is no way for natural selection to select for reliable belief-producing cognitive faculties.

So any way you look at it, physicalism is an irrational point of view. It undermines the necessary preconditions to make any of your beliefs rational. So to be rational, you must reject physicalism, and if you reject physicalism, you should be open to the supernatural.

No comments: