Physicalism is the philosophical position that holds that everything is physical and that there is nothing over and above the physical. This includes substances that are still subject to debate, like abstract entities (numbers or concepts like justice, for example), consciousness/ qualia, spiritual experiences, morality, and more.
General Argument:
Premise 1: All of our successful scientific theories thus far have shown that many things once thought to be or caused by non-physical things were found to be physical.
Premise 2: Via induction, if something frequently occurs in the past, it is more likely to happen in the future.
Conclusion: We should think that phenomena that we now have reason to think are non-physical will be found to be physical.
Briefly, a successful theory is one that can explain all the phenomena without positing the existence of unnecessary objects and can hopefully make testable and accurate predictions about the future.
Examples of Explanations:
There are tons of examples where people thought that something was caused by non-physical forces but eventually realized that it had a physical causes. I will go over a few here:
Intelligent Design: For most of human history, it was thought that only an intelligent designer could have created all the biological sophistication that we see on Earth. Later, however, we learned about the theory of evolution, which explains how extremely sophisticated biological traits and parts can arise from very simple, fundamental rules like natural selection.
Rainbows: During the times of the Bible, rainbows were thought to be a sign of the covenant between God and the earth:
God further said, “This is the sign that I set for the covenant between Me and you, and every living creature with you, for all ages to come. I have set My bow in the clouds, and it shall serve as a sign of the covenant between Me and the earth.
It was later found out that rainbows are actually not supernatural and come about by material causes. Particularly, rainbows form when sunlight is refracted, dispersed, and reflected in water droplets in the atmosphere, causing a spectrum of light to appear. The light enters a droplet, is refracted at the droplet's surface, reflects off the back of the droplet, and then refracts again as it exits, creating a circular arc of colors.
Personality and Behavior: People once used various non-physical theories to explain psychological differences among people — some people thought that immaterial souls and spirits influenced how we behave, especially those with mental illness.
However, it is now understood that personality and behavior can be explained by appealing to material causes like brain chemistry, genetics, neural structures, and environmental factors.
Infectious Diseases: People used to think that infectious diseases—like the black death—arose from non-physical sources such as divine punishment or astrological events. Once again, these were later found to be wrong and replaced with significantly better physical theories.
“But this time is different!”
Many non-physicalists object to this claim by arguing that some things now (qualia, cause of the universe, etc) are fundamentally different than the things we’ve discovered earlier. There are three main points that non-physicalists can use: 1) we have good object-level reasons to think that this time is going to be different, 2) materialist theories are incomplete, and 3) if we think that the universe is mostly physical, we would expect that physical theories would have done really well in the past. In the next sections, I will attempt to defend physicalism from these arguments.
Defense #1 — A Similarly Scientific Inductive Case:
Science is almost entirely done using inductive reasoning, which uses past observations to draw on general conclusions—laws of nature, for instance. Without inductive reasoning, we would have no prior knowledge to work off of and science would repeatedly ask the same questions to make sure previously held assumptions still hold.
For example, imagine that you are exploring a remote wilderness and come across an animal that doesn’t look like anything you’ve ever seen before. After doing some research and finding no information about it online, you send it to a database that has access to all known species. To your surprise, it says that you have found a new species and cannot determine what animals it may have evolved from.
Is it now reasonable to think that this animal was evolved via evolution, especially considering that it doesn’t look like any other animal that has evolved? The answer is obviously yes; so many animals that were once thought not to have been evolved have shown to be evolved. On this basis, it is reasonable to think that this animal was evolved via evolution because of meta-level considerations (evolution has developed every other animal), despite object-level counterarguments (this animal looks different than others).
Similarly, in the argument from meta-induction for physicalism, we should be able to derive generalizations from many instances of cases, despite compelling object-level differences.
Defense #2 — Incomplete Non-Physical Theories:
Non-physical explanations are usually not precisely defined nor do they explain how these causes come about. For example, panpsychists (who believe that consciousness is a fundamental part of the universe typically in response to The Hard Problem) don’t make testable claims — they usually just assert the existence of some property that cannot be precisely defined among other issues. In this case, there is the Combination Problem, which asks how micro level conscious experiences combine to form unified, macro-level conscious experiences, and the Interaction Problem (a problem for dualists, as well), which asks how fundamental consciousness interacts with physical processes.
Another example might be thinking that the cosmological constant is fine-tuned by a non-physical source like God. The existence of God also raises many questions — where did God come from, how and why does God casually interact with the physical, etc. In this case, despite object level considerations for why this time may be different, we should take meta level considerations into account as well.
Once these immaterial theories have their own issues (like explaining the interaction of the immaterial to the material), they seem to be in a similar explanatory position to the physical theories, except that they don’t have the meta-inductive point for physicalism. On this basis, we should have good reason to reject these non-physicalist theories.
The second objection requires an understanding of the problem of induction, as will be explained in the next section:
Defense #3 — The Problem of Grue:
This problem of induction was developed by Nelson Goodman.
Imagine that you are a miner in a cave, and it is a known fact that all the emeralds that have ever been that have found have been green. Because of this, every single new emerald found thus far has increased the likelihood of the proposition P being true; whereas P represents the claim that all emeralds are green.
On the other hand, another miner (miner 2) starts off with the proposition Q; whereas Q represents that all emeralds are grue. Grue is defined as green before some time in the future, let’s call it time T, and blue after time T. Because miner 2 predicts that we will have only found green emeralds so far, he can claim that all emeralds that have been found increases the likelihood of Q being true.
From the perspective of both hypotheses predicting the same evidence, one might argue that finding green emeralds before time T should equally increase the likelihood of propositions P and Q being true, but this doesn’t seem true. It seems like the fact that we’ve found only green emeralds in the past means that we will find green emeralds in the future, not grue emeralds (despite proposition Q anticipating the same experience).
While there have been many answers to this problem (appealing to simplicity, more natural properties, etc), without relying on a specific solution, I will condition on the fact that the proposition P is more likely than Q.
Similarly, in the case of physicalism, claiming that we would expect to find many physical phenomena before non-physical phenomena simply because there are more physical things is problematic. This is like assuming that finding green emeralds equally supports the hypothesis that all emeralds are green and the hypothesis that all emeralds are grue. Just as the green hypothesis is more likely based on past observations, physicalism is more likely based on the historical success of physical explanations.
As always, tell me why I’m wrong!
There's a hugely important difference between other reductions and reductions of consciousness to physical stuff. All the other reductions are about behavior. And sure, perhaps we can explain how things behaves in terms of physical stuff. But the fact that we can successfully explain behavior--and this gives us a reason to be skeptical of Behe's arguments, for instance, for intelligent design--doesn't give us reason to think that we can explain subjective experience which is about what it's like to be in a certain state, not a fact of how that state behaves.
In fact, I'd go so far as to say there are other inductive arguments going the other way. Not a single mental state has ever been successfully reduced. And there are many examples in history of people saying things that appear radically different are reducible to each other--take, for instance, the claim among mechanist that action at a distance reduced to mechanical pulling or the claim of the Greeks that everything was made of fire/water/air/earth/some combination/the apeiron.
As Goff notes, the physical sciences were never intended by Galileo to reduce everything. Galileo's radical thesis--which has been majorly vindicated--was that everything other than consciousness could be reduced to underlying physical causes.
It can also be dangerous to carry linear extrapolation too far! One of the reasons that the things under consideration like consciousness and mathematical facts have resisted reduction may be that unlike the things we've reduced, they can't be reduced even in principle. The fact that reduction covers the easy cases doesn't show it covers the difficult cases.
This is a well written and clearly argued article.
But from a non-physicalist point of view, it reduces to question begging. In premise 1 you appeal to all the “many things” that have been successfully explained by science. What do they have in common? It was possible to explain them with scientific methods.
A helpful distinction here would be between super-natural and preter-natural. Supernatural means something that is - in fact - beyond nature, whereas preternatural means having the appearance of being divine.
Preternatural is things we don’t understand how they function, or what they are, so it’s not only unsurprising, but entirely expected that preternatural things would be steadily explained as science progresses in understanding the natural world.
Whereas supernatural means it’s of an entirely different order of things. So we’d expect to find it can’t be explained by physics.
And I think the two things the non-physicalist can definitively point to are qualia (and intentionality) as well as the cause of the natural world itself. Both of these have logical arguments why science can never explain them.