In contemporary philosophy, the orthodox view is "Physicalism." As it pertains to us, Physicalism is the view that we are physical objects. Perhaps we are indentical with bodies, or more plausibly we are identical with some part of bodies, for example brains. So let's take it that if Physicalism is true (as most philosophers believe), then you are identical with a brain. Which brain? That one behind your eyes.

Now if A is identical with B, then wherever A goes, B goes, and whatever happens to A happens to B. For example, Clark Kent is identical with Superman. If Clark Kent goes to the library, Superman goes to the library. If Clark Kent cuts his finger, Superman cuts his finger. And if Clark Kent dies, Superman dies too.

Now consider your relationship with that brain behind your eyes. If physicalism is true, you just are that brain. So whatever happens to that brain happens to you. Now within 100 years, that brain will be decomposing inside a wooden box, six feet underground. If physicalism is true, that means that you too will be decomposing. When your brain ceases to exist (which it will), you cease to exist. And so then there is no life after death, if physicalism is true. Life ends at the grave.

The alternative to physicalism is "Substance Dualism," the view that you are not identical with any physical object. You are instead a nonphysical object, capable of surviving the death of your body. You are an immaterial thing that thinks and feels, what philosophers have often called a "soul." You don't have a soul according to Substance Dualism, you are a soul. That's what people are, essentially: immaterial thinking, feeling things. Not brains. If Substance Dualism is true, life after death is possible. You may survive the death of your brain, since you are not your brain.

Now here's an argument for Substance Dualism (from the contemporary philosopher Richard Swinburne). First, consider a lump of clay (see picture above). Suppose we call the lump "Lumpy," and then cut Lumpy perfectly in half, and put one half to the left and one half to the right. Now suppose I asked you "What happened to Lumpy?" It seems to me that the obvious answer is fully satisfactory: 1/2 of Lumpy is on the left, and 1/2 of Lumpy is on the right. Lumpy got cut in half, end of story.

But now consider brains. Brains consist of two hemispheres connected via the corpus callosum. We know that people can survive the severing of the corpus callosum (a procedure known as a commissurotomy; historically used to treat epilepsy), and can even survive the loss of an entire hemisphere. And it seems in principle possible that one day brain transplants will be technologically feasible. We can already transplant livers, kidneys, lungs, and hearts. It's only a matter of time before we can transplant brains.

Alright, so suppose one day when such brain-transplant technology is available, someone endeavors to sever a subject's corpus callosum, and transplant each hemisphere into a separate vacated skull. Suppose the subject is named "Alan." The surgical plan is to separate his hemispheres, and then put the left one in a waiting, vacated skull (call it "L"), and the right one in another waiting, vacated skull (call it "R"). Alan's original skull, then vacated, will be destroyed along with his original body.

Here's the question: What happened to Alan?

In the case of Lumpy the lump of clay, the plausible answer was that Lumpy was 1/2 on the left and 1/2 on the right. But that answer doesn't seem plausible in the case of people. People can't be 1/2 on the left and 1/2 on the right. People, subjects of experiences, don't come in halves - a person is either there or not there. After the surgery, L and R will both regain consciousness and go on with their lives. One may move to Idaho, say, and the other may move to South Africa. Can we really make sense of the idea that, in that case, Alan is now 1/2 in Idaho and 1/2 in South Africa? One person is in two places with two completely independent streams of consciousness? No, that doesn't make sense at all.

But then there are only three options for what happened to Alan:

(Option 1) Alan is now in body L.

(Option 2) Alan is now in body R.

(Option 3) Alan did not survive the operation. He ceased to exist.

Which of these is true? What happened to Alan? The fact is each option seems equally plausible. Each one is certainly logically possible, and it's hard to see how we could figure out which one actually happened from our perspective as neurosurgeons.

But then we have a compelling argument for Substance Dualism, a compelling argument that Alan is not identical with any physical object. I'll explain exactly how this argument goes in my next post.