Matter in Action

I’m reading up on Thomas Aquinas this month and it struck me for the first time that the concept of “agency” stretches like a great gap between the Renaissance and today. It appears to be a major sticking point for modern worldviews, so I’d like to spend a little time on why – and how – it was important historically.

First, we must remove the “philosophy” and speak common-sensically. I usually take the opposite tack, but here a little common sense may be useful. When I leave my book on the table, I expect it to stay there. Books don’t move themselves. When I throw a ball, I expect it to fly away from me and not return. We have confidence that some things (like steamboats) move under their own power while other things (like sailboats) rely on outside forces. Nothing fancy needs to be inferred or implied.

In Antiquity, Aristotle and others felt this was a very important concept. They said that some things – such as animals – move on their own while other things – such as rocks and books – do not. They called the ability to act agency and the ability to be acted upon passion.

Let us take a purely mechanical metaphor. Consider a modified tetherball, with a pole, an elastic tether (like a bungee cord), and a ball. When you hit the ball, it moves. The ball is passive to your force. When the ball moves, the rope moves with it. It acts as an agent on a patient. The pole is impassive. Even though connected to the tether, it doesn’t move when the tether does.

The distinction raises a couple interesting issues. First, consider the movability of the pole. The tether won’t move it, but a bulldozer would. So we cannot say the pole is completely impassive. Second, consider the motion of the tether. The force of ball made the tether move, but it also stretched it out. The tether will contract and pull the ball back in. The ball acts on the tether and then the tether acts on the ball. The tether has “agency,” but only because it was acted on first. It has no independent agency.

Antique, Medieval, and Renaissance thinkers were interested in knowing what has agency and what has independent agency. What things will scuttle away when I set them down (or fly away, or unfold, or breakdown…) and what things will simply sit there? For the most part, they argued that matter (the stuff you can touch) doesn’t have agency, though it could be organized in ways that do. “Form” was necessary, because it allowed you to have patterns of matter that might “do” something when left alone.

The question was re-framed in the Enlightenment in terms of “potential energy” (aka the ability to do work). You’re probably familiar with two of the most fundamental laws of science. Newton’s first law of motion states that an object in motion will stay in motion (in the same direction) and an object at rest will stay at rest, unless acted on by an external force. This could be restated as: material objects have no independent agency with regard to motion. The second law of thermodynamics states that an isolated system cannot increase in terms of order. In other words, systems have no independent agency. Neither matter nor systems of matter have independent agency. Everything simply reacts to other things. The tether ball slows down as the speed of the ball gets converted into the speed of the ball/tether system plus the potential energy building up in the tether. (We also lose a bit of energy to heat and friction as it passes through the air).

Under the Enlightenment model, the atoms that make up matter have no independent agency – the speed and potential energy have to come from somewhere. Some argued that the human who hits the ball has independent agency. Others said the human system was just like the ball/tether system, acting in response to outside forces.

We now know that matter comes with internal forces for everyday objects. Our cells are made up of molecules, our molecules of atoms, and our atoms of fundamental particles (electrons and quarks). Systems of fundamental particles store potential energy, but we still think of the forces providing the energy as external to the particles. We think of them as universal forces – gravitation, electromagnetism, the strong force, and the weak force.

We still want to know, however, whether the book will get up and walk away. Aristotle thought things fell as a result of the nature of matter. Heavy things contain particles of earth that incline downward by their nature (fusiV, the origin of the word physics). This is no more mysterious than the modern notion of gravity, where masses attract one another at a distance. Aristotle called this kind of motion necessity. The nature of matter caused changes in the world. He worried though, that this necessity was not enough to explain a crab scuttling away when you set it down. Some systems must have a nature above and beyond the nature of material particles. That nature – that principle of motion – he thought was more complicated than “down” (earth, water) or “up” (air, fire) or “steady on in a circle” (aether).

Life in particular caught his attention. Living systems have very complicated agency, which makes it hard to tell whether it is independent or reducible to necessity. For him, the “form” of the system added something that purely passive matter could not. He invokes the “soul” as the nature of the system that is not reducible to the nature of the matter.

Descartes, trying to make the universe easier to understand, stuck with passive matter and moved all agency to the realm of mind. God produced all potential energy at the beginning of time and humans continue to act on matter, but otherwise, the universe is simply reacting, like the tetherball flying back toward you. Subsequent materialists have argued that matter is all there is, but tend to sidestep agency. Where did the potential energy come from? Is new energy generated? It’s easy to say it’s all reaction, all complicated passivity until you think critically about what we are reacting to…

When Ancient and Medieval thinkers speak of the nature of aether, it may sound silly. It may sound even sillier when they start speaking of the souls of planets or individual angels pushing planets. We should be slow to judge, however. It was not until the seventeenth century that we came up with a better explanation of planetary orbits than the tendency of celestial objects to move in circles. Constant motion in a circle turns out to be rather difficult to explain; only in the last two decades have we developed decent models of the Solar System that don’t require planets to fly away or spiral inward. Souls and angels answered a very important question.

I’d like to think we’re making progress with biology, but we’re not nearly as close as the astronomers. What makes the living crab scuttle away when the dead crab does not? Why do crabs scuttle and rocks do not? In science, we want universal forces acting on passive particles to be enough. We have a good idea of the agency of organisms – how they change their environment. We have a good idea of the necessity of matter within them – how universal forces act on particles. What we don’t have is strong evidence that the latter cause the former. We can’t say whether


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