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The line between physics and metaphysics: musings on Descartes and phenomenology


November 22, 2020

7 min read

Descartes' Tree of Knowledge

For a program called The Knowledge Society, I've been spending my morning commutes the past two weeks reading through the Internet Encyclopedia of Philosophy and Stanford Encyclopedia of Philosophy's introductions to Renes Descartes. Two months ago, I had attempted to do the same for Nietszche, but struggled to come to any valuable understandings beyond surface-level connections to the Existentialist philosophy of Kierkegaard and Sartre. I was afraid that I would find the same with Descartes, but this wasn't the case. Nietszche was an approximate contemporary of the philosophers I already knew, but Descartes is a close predecessor, his ideas both the groundwork for and rejected antecedents for the later frameworks I (currently and loosely) hold as my own. This sparked some thoughts about the relationship between physics and metaphysics, the nature of truth, and the progression of knowledge over time that found their way into rambling conversations and eventually this blog post.

The "Father of Modern Philosophy"

Born in 1596, Descartes worked in the middle of the scientific revolution. SEP describes him as a "mathematician first," a "natural philosopher" second, and metaphysician third. He's often referred to as the "father of modern philosophy", and we're reminded of his contributions to math and science every time we use Cartesian coordinates.

What was this "modern philosophy" that Descartes brought about? Put simply, Descartes advocated for a mathematical, mechanistic interpretation of existence and reality. The old philosophy he broke away from was Scholastic-Aristotlelianism, which held "substantial forms" to be the cause of properties and behaviors of things in the world. "The goal of being a swallow is the cause of the swallow's ability to fly...a swallow flies for the sake of being a swallow," IEP offers as an example of this. Descartes rejected this kind of thinking as incapable of creating progress, instead seeking explanations for phenomena through "the configuration and motion of parts" without reference to the abstract natures of objects.

To us, 400 years after the scientific revolution, this is intuitive. Of course the properties of an object are explained by what it's made up of, not some sort of "swallow-ness" or "thing-ness". Taking a step back though, the larger question of how to think about the properties and existence of things is far from a clear-cut one. Descartes poses the hypothetical: what if we were all under the influence of a malicious devil, set on deceiving us at every turn? A similar modern equivalent might be: what if we were all just brains floating in jars in hyper-realistic VR systems feeding us experiences of things that didn't actually exist?

Descartes has a lot to say on the topic, especially proving the existence of a God who is perfect in every way. His proofs run into the problem of the "Cartesian circle", a logical loop that some scholars say cause much of his philosophy to come crashing down. Discussion around religion in philosophy can be super interesting -- my personal most-referenced philosophy is even Soren Kierkegaard's existentialist justification for Christian faith -- but Descartes' discussion didn't seem the most interesting. What did catch my interest was the overall ontology that Descartes laid out for the nature of reality.

God, mind, and matter

Descartes didn't abandon substantial forms entirely, he just greatly reduced his dependence on them to explain things. To Descartes, there are only three "substances": abstract elements that formed the foundations for everything that exists. First first of these forms is God. God contains an "infinite reality," Descartes says, able to exist on his own without any conditions. The second of these forms is mind -- this is where the famous "I think, therefore I am" comes into play. Thoughts exist in a space more abstract than the body or the world; it maintains its existence even if everything fed to it is deception (going back to our devil or VR hypotheticals from earlier). Mind is second to God, though, because mind requires God to exist. Third and last of Descartes' forms is matter, characterized by "extension" in physical reality. Rejecting distinctions such as "swallowness," the category of matter holds that there is no fundamental difference in the nature of all things in the physical world, including your own body and senses. (In other words, understanding the physical world is a matter of physics, not metaphysics.)

This ontology is much less intuitive than the earlier general mechanistic tendencies. Indeed, scholars have pointed out various flaws: the dubious proofs for God's existence mentioned earlier, and also the issue that, if mind is fundamentally different from body -- mind not posessing any extension in the physical world, and body not posessing any way to go beyond the physical world -- how do they interface and interact? A lot of thought has gone into these questions, of course, but to me they point to a more general thought about metaphysical frameworks like Descartes'.

That idea: "truth exists only insofar as it is useful."

The line between physical and metaphysical

I'll preface this discussion by saying that I'm not at all well-read in subjects of epistemology or ontology. What I'm about to lay out are musings based on the little bits of existentialist and phenomenological philosophy that I have read, and my understanding of Descartes' philosophy from a few encyclopedia entries.

That said, consider the following: why did Descartes set the line between abstract and physical existence between the mind and the body? Previously, the line between the physical and metaphysical was set a good amount beyond the body. Senses were considered to be the sources of truth, and objects' properties were believed to be explained by their fundamental natures. That's because there was no good alternative. If the senses couldn't be trusted to understand the world, then what could?

The scientific revolution brought math and science as a new alternative. Suddenly, it made more sense to explain things in terms of the forces of physics, or consistent chemical reactions, rather than through abstract ideas. With the better marker of truth that is physics, the realm of metaphysics was pushed back. The operations of the mind still could not be explained by physics, so that's where Descartes drew the line, declaring "thinking" an abstract matter that transcended mechanistic explanation.

The past few centuries of scientific progress have revealed that even the mind is more mechanistic than then thought. We now have tools like neuroscience and genomics, fields that are both still rapidly developing and bound only to generate further insights and updates to our understanding. Alongside this scientific progress, philosophy and metaphysics by the 20th century had re-calibrated as well.


Phenomenology -- or my understanding of it through David Abram's The Spell of the Sensuous -- can be nicely explained in the same terms as Descartes' ontology. Ignoring the category of God, Descartes sets the position of metaphysical ground truth at the level of the mind. "I think, therefore I am" is a foundational, axiomatic base from which all other knowledge is constructed. The senses, and all the things that exist in the physical universe, are external to this; they are "extensions", of a lesser reality. Phenomenology sets the metaphysical ground truth one level further back than even the mind.

I'll first use an example to explain. Imagine you are meditating. As you go through your breathing exercises or what have you and settle down, your thoughts calm and disappear. Your sense of time slips away. You're left isolated from your senses of the world around you, and even of your own body. You perceive them, but they're external to you, just as Descartes says. But now go one level deeper. In a moment of complete peace, when your thoughts really are calm, you're not bound to your consciousness or thoughts any more than you are to your body. Sure, thoughts might pop into your field of existence, but the point of meditation is that you can let them pass by and be without them again. In other words, your thoughts have become just as external to you as your senses.

If your thoughts are external to you, then your existence can't be defined in terms of your thoughts. You must be something more than your thoughts, then. You exist as an abstract entity, to which your thoughts and senses and external objects alike feed into externally. Or maybe you are all of these things combined, the sum of all your thoughts and experiences and the things that cause them, with no distinction between internal and external.

What we've just done is transcend Descartes' separation of mind and body. But like Descartes, we haven't eliminated substantial forms, we've just created new ones. Descartes could have taken the same steps outlined here, but it would have been less useful. Today, we have neuroscience to explain that our brains are just complex biological computers with predictable behavior. What that knowledge, it's extremely compelling to look for a characterization of existence that doesn't center around the mind. Descartes didn't have a rigorous way to explain the mind mechanistically, though, so it didn't make sense for him to abandon metaphysics at this level. For now, we can't use physics (science) to explain the nature of our existence, so this must remain in the realm of metaphysics.

The Tree of Knowledge

A last idea of Descartes' illustrates some thoughts I've come to in this blog post: the tree of knowledge. The root of Descartes' tree of knowledge represents metaphysics. The trunk is physics, and the branches and fruits are its eventual applications: mechanics, medicine, ethics, etc.

Descartes' Tree of Knowledge

I didn't think much of this breakdown at first, but looking back on it now, it illustrates the relationship between physics and metaphysics that has been my main takeaway from my brief study of Descartes. Both are part of the tree of knowledge, made of the same wood, not fundamentally different. The only difference is that physics (i.e. all science) is above ground, able to rigorously and logically explain real-world phenomena, while metaphysics are below ground, dealing with the domains of knowledge that we've yet to -- or may never -- decipher. Physics are necessarily dependant on metaphysics, but it can also push back: metaphysical roots grow in new and deeper directions as the trunk and branches grow above it. Domains of metaphysics have been replaced, or at least greatly impacted, by the development of physics in past centuries, and surely centuries more to come (admittedly here the tree analogy breaks down a little bit).

I'll close by saying that again, I'm not well read at all on ideas in epistemology or ontology that would seem to be highly applicable here. This post's thought, that what we consider to be physics and metaphysics are related and ever-changing things, based largely on what truths are "useful" at a given point in time or historical circumstance rather than an absolute, objective truth, are ideas that have been swirling around in my head and clarified with recent reading and conversations. It's these kind of thoughts, though -- shaped by the influence of thinkers historical and around me today -- that make up a person's continually updating understanding of self, existence, and reality. I'll continue to gradually take in thoughts of various forms -- less gradually so if I start university where I want next year -- and update my own understandings.

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