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Physicalism is the view that the ultimate constituents of the world are something other than conscious entities. (There are actually many ways to define physicalism, but this is the definition that will be most useful here.) Physicalism is often viewed as the simplest theory of reality, because it doesn’t postulate any mysterious “mind stuff” over and above the physical world.

However, the simplicity argument for physicalism ignores one very important fact: Our only acquaintance with the nature of the physical world comes by way of conscious experience. Interestingly, once we take this necessary starting point into account, we end up with the result that physicalism is not the simplest theory after all.

The argument goes like this:

The only concrete properties to which we have any direct access are the properties of our own conscious experience: the colors, sounds, shapes, smells, tastes, and sensations that philosophers call “qualia.” Now, these properties of our experience appear to change over time in a semi-patterned, semi-predictable way. The most common way of explaining these regularities in the qualitative properties of our conscious experience is by appeal to our changing relationship to something outside of our conscious experience that's nevertheless affecting it. Generally, this “something” outside our conscious experience is taken to be the physical world.

But what is the physical world?

Well, if one wanted to be as parsimonious as possible and not hypothesize any kind of entity beyond what we absolutely know to exist, one would have to say that the physical world is nothing but the regularities we observe in our conscious experience. That is, one would have to say that the physical world is just an abstraction from the concrete givens of conscious experience. We might call people who hold this view “eliminativists” about the physical.

However, most people—philosophers included—are inclined to postulate that the physical world has more “substance” to it than this. That is, they are inclined to the belief that the physical world has some measure of existence independent of our conscious experience, that it has some sort of concrete properties of its own that in turn causally affect our experience.

Although it’s not obvious that the existence of an independent, persisting entity is any more explanatory than the regularities themselves, let’s assume that it is, and thus that it does make sense to conclude that the physical world has concrete properties of its own, properties that it has in itself, over and above the way it affects our conscious experience of it. What sort of properties could these be?

Now, although the only concrete properties of which we have any knowledge are the qualitative properties of our conscious experience, we could postulate that the physical world has some other sort of concrete properties—properties completely different from the properties of our experience and properties of which we have no knowledge and never will. However, it would be much less ontologically extravagant to infer the inner nature of the physical world from the sorts of properties with which we are familiar: the qualitative properties of conscious experience. If we do this, we end up with the idea that the physical world itself has qualitative consciousness of some sort.

This view will seem radical and strange to many people, but it has recently been gaining a following among philosophers. Some of these philosophers, called “microexperientialists” or “micropsychists,” take qualitative experience to exist at the micro-level of the physical world, and see larger physical objects as being built up from these microexperiential objects. (For a classic statement of this view, see Strawson 2006.) Other philosophers see the nature of the physical world as being holistic. They see the universe as ultimately having only one mind, of which the various parts of the universe are aspects. (See, for instance, Goff 2017 and Kastrup 2019.) This holistic view is referred to as “cosmopsychism” (Shani 2015).

While consciousness-based theories of reality are still in the early stages of development (at least as regards their 21st-century forms), there are multiple motivations for developing such theories, which include their ability to solve the “hard problem” of consciousness as well as the characteristic we've just seen: their elegant ontological simplicity. Instead of positing the existence of mysterious “physical stuff,” these consciousness-based theories build their conception of reality exclusively from materials with which we are intimately familiar: the qualitative properties of conscious experience.

In the end, it’s simply not true that physicalism is the simplest theory of reality. It’s much simpler to believe that, if the physical world has an independent existence at all, it’s just another form of consciousness.