Platonic versus Aristotelian Causality

Tom asked a question about how things are caused in the post about the philosophy of abortion. This is exactly the sort of question that most people will find impossibly irritating, dense, arcane, and useless to consider; it is also, therefore, exactly the sort of question I love to think about. Aristotle says that the highest things are of course useless: to be useful is to be good for something else, as a tool is good for being able to perform a repair, and the repair is good for being able to return to using the truck, and the truck is good for being able to fetch food for yourself and your family, and the food is good for feeding the people you love so that they won't die. The people you love, though, are good for their own sake: they may not be useful at all. Nevertheless they can become the focus of your whole life: especially a baby is not useful but readily becomes the focus of the parents' lives for quite some time.

So too philosophy, especially metaphysics: it may not be useful at all, but that is because it is the study of the very highest things.

So I'm going to answer this question at length. Out of courtesy for the rest of you, I'll put it beyond a jump break so that you can dodge the question if you want.

OK, for those of you who are still here, let's go through the differences between Plato and Aristotle's approach to physics and metaphysics, and why you can't readily synthesize them. It will be helpful to read the comment thread that originated this discussion.

Aristotle and Plato both agree that physical reality is composed of things that are made of form and matter. Such a system is called hylomorphic, hyle (pr. HOO-lay) being the Greek for 'matter' and morph for the form that something takes. Their models nevertheless differ fundamentally. For Plato, the Form of the thing is a kind of idea that lives in a mind -- probably a divine mind, which later monotheistic thinkers recognized as the Mind of God. The physical thing is a kind of manifestation of a divine Idea, which has the physical 'form' that it has because it the matter is being ordered that way by the divine power. Many religious thinkers have liked this approach for obvious reasons, but it has also appealed to brilliant scientists like Einstein as well as rationalist philosophers like Kant (more on that later).

Aristotle has a much simpler-to-grasp idea: the form, he proposes, is in the thing. Consider the parts of a table, all lying in a heap on the floor. All the same material parts are there as the table would have, but it is not a table until it is put into the correct form. The form is thus immaterial: it is the way the material is ordered. Once the form is in the thing, the thing comes to be what it is: a table, whereas before it was a heap.

Aristotle's system still has a divine mind that is thinking about divine thoughts -- thought thinking itself -- but it is not transcendent like Plato's. These are the unmoved movers. They do end up driving the whole universe, as it happens, but not in the same way that Plato thought: their immaterial perfection, being pure form without matter, is so admirable that those beings who can see them try to imitate them as best as they can. These motions aim at circularity, because the circle is the closest thing to a perfect motion that a material being can obtain; and that is why the stars circle the Earth, because they are imitating the unmoved mover as well as they can. This keeps the universe in motion and accounts for most of the movement in reality, except in the sublunar realm where we are (and also where things are strangely worse; there is corruption here, and not above).

Monotheists who followed Aristotle, such as Aquinas and Avicenna and Maimonides and Gersonides, dispose of all the unmoved movers except one, who is God. They have increasingly disposed of the whole account of motion, which in the early Modern era proved to be implausible. It seemed pretty good for a long time, though: you can see that the stars move in circles around the earth by direct observation of them. Just watch, they do it every night. Thus earth must be at the center of the universe. Why? Well, it seems to be its natural place: pick up a piece of the earth, like a rock, and drop it. It moves toward the center of the universe, i.e., down. Water falls from the sky and forms lakes on top of the earth, and if you drop your rock into the water it goes to the bottom. Thus the element of earth has a natural place at the center of the universe; water above that; air above that; and if you light a fire, it goes up towards the stars. Thus, we can see how the universe is ordered by direct observation. That sounded good for a long time, and you probably have heard the story about how it stopped sounding good.

Anyway, a consequence of this approach is that Aristotle was much more interested in what we would today call physical science -- he called in the science of nature, ϕυσικά, which gives us our word physics. (For most of the period this was called natural philosophy, a term Newton was still using.) Because the form is in the thing, we can come to know it and its causal properties; and because the form is so tightly connected with the end or purpose of a thing, telos, the formal and final causes are often the same. A science of nature makes sense, then, because we are studying the forms -- the order in which things are -- and also the matter that is in those forms, and thus we can make an orderly investigation and study of nature.

Plato doesn't write a lot about physics, because he believes the Forms that are the ultimate causes of things are not readily observable. He gives an account of this in the Republic, in his famous Parable of the Cave. Most people are like people strapped into their seats in a cave, with a big fire behind them that is causing shadows to be cast on the wall in front of them. The reality they think they observe is the interaction of these shadows, but they are unable to see what is really producing the shadows. Think of shadow puppets made with your fingers, that look like rabbits or whatever but are really quite different than their appearance as a shadow suggests. Only the philosopher is able to get free and realize what is going on; and the best philosopher can go beyond that, getting out of the cave and its fire in order to experience the sun and the world. Most people never do that, but spend their lives focused on the shadow drama. 

There's not much point in studying the shadow-drama, then: it's not real. Physics becomes much less interesting if it is not able to approach real, capital-T Truth. It's still useful for engineers, but notice that it is merely useful. It is not the highest thing, because it's just a tool for obtaining other things that matter more. Plato's aims are higher.

The Aristotelian and Platonic causal systems thus don't blend well enough to synthesize them. They're talking about two different pictures of reality, and differ sharply on the question of how much we can know about reality by observing physics. In the Modern age, this clash played out again with Newton et al taking the Aristotelian position that there were laws of nature we could identify and come to know through study. David Hume rejected that idea, arguing that 'the secret springs of nature' were hidden to us; Newton could say a lot about gravity, for example, except exactly what it was and what caused it. (Newton admitted as much; he described the inverse square law of gravity, but as to why things worked that way he wrote 'I make no hypotheses.') Hume said that we, like observers of the shadow puppet show, could only talk about things that we observed happening together -- but we couldn't be sure why they happened together, and the fact that they did might be a mere coincidence that just happened to occur over and over. The source of the Forms behind the show remains hidden.

Immanuel Kant tried to reconcile this in his first critique, but he ended up making it worse. He recognized this distinction between phenomena, the stuff we can encounter and observe, and noumena, the things as they really are. Kant went on to prove, devastatingly, that the nature of our minds makes it impossible to ever observe or encounter noumena at all: phenomena are all we will ever have. Thus there is no possibility of learning the capital-T Truth about anything outside of our minds; useful study of phenomena is all we'll ever have. Kant denies both the Aristotelian/Newtonian concept that we can obtain the truth by studying nature, and the Platonic idea that we can obtain the truth through philosophical reflection.

Obviously we can still do lots of useful things, though; physics remains worthwhile as a handmaiden to engineering. As a road to Truth, however, it is closed.