What I Mean By "Physicalism"

Everything Is Physical, But The Physical Isn't Everything

Physicalism is often presented as the thesis that the world as described by physics is all that really exists, or is the “fundamental reality” everything else depends upon. That is not what I mean. In this post, I am going to reject that framing, while defending an alternative conception of physicalism: one that is less metaphysically rigid and that can answer Hempel’s dilemma.

By “physicalism”, I mean that everything that exists could (in principle) be given a comprehensive description in terms of physics, such that everything there is to know about the thing could (in principle) be worked out from the physical description.

Let me unpack this a bit.

What is “physics”?

What do I mean by “physics” here? I believe that all of reality is relational structure, and I would say that “physics” represents the most simple microstructural aspects of that structure. And I would add that these microstructural aspects lack the characteristic features of minds, such as intentionality. This can be neatly expressed using the language of Aristotle’s four causes. Physics, in a very broad sense, is looking at the world in terms of its simplest material causes (the parts that constitute a thing¹) and efficient causes (how a thing was brought about by the past), while excluding formal causes (the unified whole that is constituted by the parts) and final causes (how a thing is directed towards the future).

This broad definition of physics avoids Hempel’s dilemma. Hempel was concerned that if physicalism is defined in terms of our present physics it is basically wrong, since we can be confident that our current theories, like previous theories, are wrong in ways we do not yet know. But if it is defined in terms of an ideal future “physics”, we have no idea what might be called “physics” in the future, and so physicalism turns out to be meaningless. By defining physics in terms of material and efficient causes and the exclusion of formal and final causes we keep what I believe is the core idea of physicalism, without overcommitting to present theories and without leaving physicalism unspecified until a later date.

Physics Isn’t The Only True Description

This is not to say that the physical description — the description in terms of the simplest microstructural elements — is what is “real” while the complex macrostructures they constitute are somehow “unreal”. Just because we could give a comprehensive description of the world in terms of its smallest parts, does not mean that that is the only true description.

In fact we could (in principle) use holistic concepts of larger and more complex things to provide a much more efficient and equally complete description of the universe. The key is to think in terms of information theory and data compression. For example, if we imagine that Laplace’s demon wanted to efficiently write down the positions and velocities of every atom in the universe, he might decide to first note the position and velocity of the centre of mass for each galaxy, star, planet, moon etc, and then record the positions and velocities of each atom that makes up the macro-entity relative to its centre of mass. As another example, if he wanted to record the location and element of every atom in a human body, he could significantly compress this information by e.g. recording the position of the skeleton and then using a shorter code to record “calcium” for the atoms within the skeleton.

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These descriptions would be no less accurate than recording the same information without utilising the information about the macrostructural elements, but they would be vastly more efficient.

This is related to the point Daniel Dennett made in his famous paper ‘Real Patterns’, although he treated real patterns more as lossy pragmatic tools. He missed the fact that real patterns (including imperfect patterns) could (in principle) be used to provide a perfect compressed description of a system in its entirety. Of course, the “in principle” is doing a lot of work in that sentence, but the same phrase is working even harder when we imagine Laplace’s demon working without real patterns!

The same point can be applied to intentionality and final causes. If you know what an animal intends to do then the behaviour of the atoms that compose the animal become far more predictable, and predictability is exactly what allows for compression and efficiency². Therefore if Laplace’s demon wanted to more efficiently describe or predict the atoms within and around an animal over a period of time, it would do well to make us of information concerning the animal’s evolutionary design and its present intentions.

Since there can be equally complete descriptions of reality which make use of other categories of thought, including formal and final causes, why should we think the physical description alone is uniquely “true” or “real” or “ultimate”?

Physics Isn’t “Fundamental Reality”

Similarly, I would not say that the physical is “fundamental” or that everything besides the stuff of fundamental physics “depends on” the physical. The physical is a description of reality, not reality itself, nor even the sole description of it.³ To say, for example, that the biological depends upon the physical is nonsense. If we are talking about descriptions, it is possible to describe a thing’s biology with minimal understanding of physics. And if we are talking about the reality being described, the physical and the biological are the same thing. To say that the cat depends upon its material constitution is to say that the cat depends upon the cat. There is no cat over and above its material constituents, and there are no material constituents over and above the cat. They are the exact same thing, being described in different ways.

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This idea of dependence is often put using the concept of “supervenience”. Phenomenon A is said to “supervene on” phenomenon B if and only if any change in phenomenon B necessarily requires a change in phenomenon A. I would agree that everything supervenes on the physical. But the physical description also supervenes on the compressed complete descriptions I described in the section above, where information about planets, bones, and intentions is utilised. The apparent asymmetry comes from treating our complex concepts as lossy compressions, where information is lost by generalizing over multiple cases, rather than recognising their potential for lossless compression, where the specific details are all encoded except more efficiently. Of course the lossless compression is, strictly speaking, imaginary and impractical, but then the uncompressed complete micro-description is even more imaginary and impractical!

There is also a tendency among many to suppose that the parts of a thing are more “real” or “fundamental” than the whole. After all, remove the parts and the whole disappears, right? But this is confusing our different conceptualizations for different metaphysical entities that are mysteriously related to one another. The whole is not something in addition to its parts, it is a conceptualization of the parts in their relational structure. This is why we can remove and replace all the parts while the whole remains, as with the ship of Theseus. Likewise, the part is not something in addition to the whole, it is a conceptualization of some particular aspect of the same thing. They are different conceptualizations of the same reality.

The idea that the are distinct “levels” of reality is confusing our conceptualizations for the thing being conceptualized. And that includes the conceptualizations we call “physics”. There is no “one true description” of reality — the same reality may be conceptualized in multiple equally true ways. To put it more bluntly, reality does not come pre-labelled.

This also means that the causal story given by physics is not the only valid causal story. We can explain why I am typing these words by saying it is caused by physical processes in my brain, or by saying it is caused by my intention to communicate this message. These are not rival causal theories, because my intentions are not something over and above the physical processes, and the physical processes are not something over and above my intentions. They are two ways of conceptualizing the same causal structure.

What Is “Everything There Is To Know”?

In my definition of physicalism at the start I wrote, “everything there is to know about the thing could (in principle) be worked out from the physical description.” This requires some elaboration.

Let’s take the example of ink marks on a piece of paper. Can the meaning of these marks be “worked out” from the physical description alone? Could it be worked out from a physical description of the entire universe?

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If we imagine Laplace’s demon with full knowledge of all facts of physics but no other knowledge, then the answer is no. In fact, the demon would not even understand the question. If confined to physics alone, the demon would lack the concepts to understand what is meant by “What is the meaning of these marks?”, and so there would be something to know that could not be worked out from the physical description alone.

But if we suppose the demon had full knowledge of all facts of physics plus the required knowledge to understand the question, then the answer is yes. Even if the marks were in a language the demon did not know, it could work out what is meant by looking at how the ink marks relate to other ink marks and how they are related to the people’s behaviours.

The physical description only implicitly contains all facts there are to be known, such that they could (in principle) be worked out, but only by those who already possess the relevant conceptual frame. The physical description does not contain or subsume alternative descriptive or interpretive frames, even though it implicitly fixes all facts within those frames.

Conclusion

So that is what I mean by “physicalism”. It is not the claim that “fundamental reality” is physical, or that the “true ontology” is that used by physicists, or that all of reality is made of a “physical substance”. It is the much more modest idea that reality can, in principle, be comprehensively described in terms of its parts and its past. Even while it can also be validly and comprehensively described in other ways too.

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1. This is a point that seems to often be missed when Aristotle’s four causes are explained. His concept of a material cause is broader than just the “matter” or “stuff” things are made of, and is more of a general part-whole distinction. For example, he considered the letters of the alphabet to be the material cause of words.

2. The basic idea is that the more common/probable something is, the more you should prioritise dealing with that thing efficiently, even at the cost of expending more on other, less common events. This is why we develop acronyms and symbolic systems to make certain calculations more efficient. Concerning the power of symbolic languages, Whitehead wrote in his ‘Introduction to Mathematics’,

By relieving the brain of all unnecessary work, a good notation sets it free to concentrate on more advanced problems, and in effect increases the mental power of the race. Before the introduction of the Arabic notation, multiplication was difficult, and the division even of integers called into play the highest mathematical faculties[…] Our modern power of easy reckoning with decimal fractions is the almost miraculous result of the gradual discovery of a perfect notation.

3. There’s an annoying slogan to this effect: “the map is not the territory.” It’s true in the sense of what I’m saying here (that we shouldn’t confuse our conceptualizations for what we’re conceptualizing itself) but it seems to often be used to deny that reality is knowable or accessible at all, which is completely false. That is not what I am saying. We really do know the world through our concepts.