We first introduced dualism as the simplest theory that makes use of a range of obvious philosophical facts. It's a theory with a logical philosophical argument behind it, in the work of Descartes. Yet dualism has taken a number of serious knocks in previous lectures, such as last time when we argued that our picture of the mental functioning that goes along with dualism, that of the inner theater, doesn't hold up very well under more careful examinations. To the extent that our inner theater is part of our obvious philosophical facts, it may not longer be so obvious that these are genuine facts, rather than just common assumptions. Dualism also faces the interaction problem. If substance dualism is true, is there are two radically different kinds of stuff in the universe, how could they possibly interact?

In this lecture we'll talk about some philosophical alternatives. If dualism isn't true, what might be true instead? Let's first talk about some alternatives within dualism. Descartes was a dualist, since it was Cartesian dualism after all. He was perfectly aware of the interaction problem, and even in his time, his critics made sure of that.

You say the mind and body are essentially different kinds of things? Then how could they possibly interact? Descartes did in fact have an answer. It doesn't appear in the Meditations, but it does appear in his 1649 book on the Passions of the Soul. He admits that the essentially different substances must interact. There is a place where mind and body are causally linked.

Where? Descartes' answer was the pineal gland. If you dissect a brain all the way down, as Descartes actually did, you would find, just about in the center of your head, sitting on top of the spinal column, a small reddish gray organ about the size of a pea. That's the pineal gland, where Descartes proposed that the mental universe meets the physical. That's where mind meets body.

Descartes had several reasons for settling on the pineal gland as the magic organ of interaction. First, most visible parts of the brain come in symmetrical pairs. You have two hemispheres, two clear sides of the hippocampus, a left and right thalamus, yet only one pineal gland.

It's also true that the pineal gland sits above the spinal column like some precious thing on a pedestal. It just looks like some spot of central importance. Finally, Descartes thought that people were essentially different from animals, that people alone had souls, as they mistakenly thought that animals didn't have a pineal gland.

Yet of course, when one thinks about it, none of this really answers the interaction question. The question is not where mind and body interact, but the question is how they possibly could. Pointing to the pineal gland, or any other physical structure, doesn't solve that basic problem. It looks like we have to face facts. Causal interaction between the mental and the physical is real and obvious. Yet it poses a crucial problem for dualism.

There are two things one could do in the face of that. One would be to give up dualism, precisely because it makes causal interaction a mystery. Or one could keep one's dualism and give up the idea that there really is causal interaction between the mental and physical.

The first root is the modern one. That's the one we'll explore through most of this lecture, because causal interaction is so obvious, that dualism has to be wrong. From the time of Descartes and a significant period afterward, people seriously explored the second route. So lets start here.

It sure does seem that there are two radically different dimensions of the universe. So maybe the idea of causal interaction is an illusion. One theory that was proposed was called epiphenomenalism. It says that maybe we're wrong about interaction. Maybe physical events don't cause mental events, or vice versa. Or maybe mental events nonetheless ride piggy back on physical events. They just come along for the ride.

It's hard to get analogies that really work, but here's a try. As a horse runs, it's shadow glides beside it. Maybe the brain is like the horse doing all the work, and the the mental realm is just it's shadow. The rush of a locomotive makes a whistling sound as it goes by. Maybe the brain is like the locomotive, doing all the work. The mind is just the whistling sound, as it rushes by.

Epi means above, and what epiphenomenalism maintains is that mental events float above physical events. There were proponents of epiphenomenalism even into the 1800s. Thomas Huxley 1825-1895 was one of them, though he was better known as Darwin's bulldog for defending the theory of evolution.

In the epiphenomenalist view, alcohol consumption doesn't cause mental confusion. What alcohol consumption causes is the particular brain state, which may in turn cause stumbling or slurred speech. It's just that the brain state casts a mental shadow, mental confusion is an epiphenomenon of that particular brain state.

OK, does that solve anything? For Patrick it just points up another question, what we mean by cause? That's a big question, one we can't pursue here in full detail. What the epiphenomenalist admits is that every time we are in a certain brain state, we find ourselves in a certain mental state. If we weren't in that brain state, we wouldn't have that mental state. That certainly sounds like a causal connection.

The analogies don't help much either. The movement of that train does cause that whistling sound. The movement of the horse does cause the movement of its shadow. Why would we see this parallel between the mental and physical if there weren't a causal connection?

Another view explored at the time, tried to answer that very question. It's called occasionalism, and the classical proponent being one Nicolas de Malebranche 1638-1715. In this view, physical events do not cause mental events. Admittedly it looks like the two go together, but that's because on every occasion, God is there, making both happen. It's as if God had a puppet in each hand, the physical puppet on one hand, and the mental on the other. God is there, minute to minute, making them dance together. Hence the illusion of interaction.

Just one step away from occasionalism is parallelism, a view championed by Gottfried Wilhelm Leibniz 1646-1716. He thought that the occasionalist view didn't offer a very dignified picture of God, with these two puppets. The God of the occasionalist is constantly meddling in the affairs of the world in order to keep the mental and the physical in sync. Hasn't he got more important things to do?

Instead, Leibniz asks us to consider two clocks running side by side, in perfect synchrony. It may look like what one does, causes the other to do the same thing, but that's not what's happening. It's just that they were wound up the same time and were sent running in parallel. That's what God does. He predetermines the physical universe and the mental universe. Leibniz calls if preestablished harmony. The two are not connected, but run in parallel since the beginning. Hence the illusion of interaction.

Epiphenomenalism, occasionalism, and parallelism. If all of those seem pretty desperate to us, we're in good company. That's the general verdict in the philosophical community today. If one has to go as far as these theories in order to save dualism, maybe dualism isn't worth saving? Maybe it's time to seriously rethink the whole question?

What of the modern alternatives to dualism? We'll lay out some major contenders to think about. As we go through them, we should be asking ourselves if we've hit upon a theory which sounds plausible to us? One that sounds right. Yet we should also give ourselves plenty of room to consider new arguments, and to change our minds.

So where do we go if we leave dualism behind? A major problem with dualism was that it gives no plausible story about interaction between the universe's two substances. Yet if interaction is the problem, it won't help to postulate more substances. If instead if two basic substances, we've postulated three or four, and went from dualism to triplism or quadruplism, we'd just have more interaction problems to answer.

No, if we're going to give up dualism, it'll be in favor of some form of monism. This includes all those views in which there is just one kind of basic stuff. The universe, whatever its complexities, is ultimately a single unified universe, composed of a single, unified, kind of stuff.