van Inwagen’s defense of physicalism

PHIL 20208
Jeff Speaks

November 2, 2006

1 Physicalism and the Ship of Theseus
2 The view that we are living organisms
3 The case for physicalism

1 Physicalism and the Ship of Theseus

van Inwagen is out to defend physicalism: the view that we are physical things, meaning that we are objects composed entirely of the particles studied in physics. (Hence the name ‘physicalism.’) This looks a lot like the view which we have been calling the ‘bodily’ view of personal identity till now but, as we’ll see, there are some complications here.

van Inwagen begins by considering an immediate problem for physicalism:

“If I am, as the physicalists say, a living organism ...then I have ‘lost’ almost all of the atoms that composed me ten years ago and I am now made almost entirely of atoms that existed ten years ago but were then parts of other things or parts of nothing at all. ...

If I am a physical thing, therefore, I am made of different matter from the matter that composed the physical thing that bore the name ‘Peter van Inwagen’ ten years ago. The physicalist is forced to say that al of our statements that imply that I existed ten years ago must be, strictly speaking, false.” (169-70)

He illustrates this problem further with the story of the Ship of Theseus. If we agree, as it seems that we should, that the Original Ship = the Reconstructed Ship, then it seems that we have to agree that, strictly speaking, physicalism leads to the conclusion that the person that bore my name ten years ago me. How can the physicalist reply to this problem? van Inwagen considers three responses:

The physicalist can accept the conclusion that my impression that I am strictly identical to the person that bore my name 10 years ago is an illusion. van Inwagen thinks that this is an overreaction; we should give up on the view that one person can exist at more than one time only if we have an unanswerable argument for this conclusion. And this argument is not unanswerable, since we could avoid it by being dualists.
We could say that although we are physical things, our identity over time is guaranteed not by sameness of our matter, but by sameness of our mental properties. This would be the response taken by defenders of the psychological view that would want to consider themselves ‘physicalists.’ van Inwagen thinks that this combination of views is incoherent:

“they mean that a hunk of matter that existed ten years ago and a hunk of matter that exists today can both be the same person ...provided only that the memories and other mental properties of the latter have ‘grown out of’ the mental properties of the former by the right sort of causal process ...but in fact no causal process can be adequate to this task. No causal process can accomplish the feat of turning one hunk of matter into another.”

What is the argument here?
van Inwagen thinks that this ‘psychological’ response to the problem of changing matter over time only makes sense if we adopt one of two views, both of which he thinks are false:
1. The relativity of identity. There is no such thing as identity simpliciter; there are only such relations as ‘being the same person as’ or ‘being the same collection of atoms as.’ How would this solve the problem posed above? Is it plausible?
2. We are four-dimensional objects, extended in time in much the same sense in which we are extended in space. How does this solve the problem of the Ship of Theseus? Can this solution be carried over to the present problem? Is it plausible?
We can say that we are living organisms, and that organisms are the kinds of things that can change its parts with the passage of time. This is van Inwagen’s view, and we turn to it next.

2 The view that we are living organisms

As van Inwagen says, the present argument against physicalism relies on the idea that physical things cannot change their parts over time. This was supported by the Ship of Theseus example. Consider the following line of reasoning (see pp. 175-6).

1.	On Monday, the thing we call “The Ship of Theseus” = the thing made up of planks 1, 2, ...1000. Lets call this thing “Monday-Theseus.”
2.	On Tuesday, plank #1000 is replaced with a new one (#1001), and taken ashore.
3.	On Tuesday, the thing we call “The Ship of Theseus” = the thing made up of plans 1,2, ...999, 1001. Let’s call this thing “Tuesday-Theseus.”
4.	On Tuesday, we can still consider the original set of planks 1,2, ...1000, even though one of them is now ashore. Let’s call the thing made up of this collection of planks “Scattered-Theseus.”
5.	On Tuesday, Tuesday-Theseus has a property which Scattered-Theseus does not – namely, containing plank #1001. So, Tuesday-Theseus Scattered-Theseus.
6.	Planks 1, 2, ...1000 remain the same from Monday to Tuesday. So, whatever they compose on Monday must be identical to whatever they compose on Tuesday. So, Monday-Theseus = Scattered-Theseus.

C.	Monday-Theseus Tuesday-Theseus. (5,6, transitivity of identity)

Since we could run a parallel argument regarding any object which loses or gains a part, this seems to show that no object can lose or gain a part while remaining the same object. But this is the claim that van Inwagen wants to reject; so he must find something wrong with this argument. In particular, he must either find a flaw in the reasoning, or reject a premise.

In fact, van Inwagen thinks that we have good reason to reject two premises in this argument: (3) and (6). Against (3): the object composed of Alpha Centauri, Stanford Hall, and my left toe. Against (6): the example of Taffy and the prehistoric fish (p. 176).

Once we see that we can resist this kind of ‘Ship of Theseus’ argument, we see that it is not only possible, but plausible to regard living organisms as the kind of things which can gain and lose parts while remaining the same thing. As van Inwagen puts it:

“The life of an animal is a kind of storm of atoms that is constantly, and very rapidly, changing its ‘membership.’ Whatever may be true or other physical objects, a living organism would seem not only to be a thing that changes its parts with the passage of time, but to be a thing whose very nature demands that it change its parts with the passage of time.” (177)

This view so far seems very plausible. But consider the following argument against the view:

Maybe organisms, and in particular human organisms, can and often do gain and lose parts. But surely this is not true of every physical object. For example, consider the set of atoms which compose me, and now consider the object, which we can call ‘My-Body-Now’, which just is that collection of (aggregate of) those atoms. We can agree that even if human organisms can remain the same despite changes in parts, collections or aggregates cannot: if we remove one member of a collection of atoms and replace it with another, we have a new, even if similar, collection. But then I have a property which My-Body-Now does not: I can gain and lose parts. So I My-Body-Now. But does this mean that there are two things sitting in my chair right now, me and My-Body-Now? And how can van Inwagen’s view count as a version of physicalism, if he has to say that I am distinct from My-Body-Now?

Think about how van Inwagen replies to the example of the Ship of Theseus. How do you think he would reply to this argument?

3 The case for physicalism

van Inwagen presents four arguments in favor of physicalism:

The interaction argument.
The argument from common speech.
The remote control argument:

“If dualism is true, our relation to our bodies is analogous to the relation of the operator of a remotely controlled device ...to that device. Now consider Alfred, who is operating a model airplane by remote control. Suppose that something ...strikes a heavy blow to the model in midair ...the blow will have no effect on Alfred, or no effect beyond his becoming aware of the blow or some of its effects on the performance of the model and his ability to control it. ...
[So] what effects should dualism lead us to expect from a blow to the body? ...The blow at the base of Alfred’s skull that in fact produces unconsciousness should, according to dualism, produce the following effects on Alfred: he experiences a sharp pain at the base of his skull; he then notes that his body is falling to the floor and that it no longer responds to his will; his visual sensations and the pain at the base of his skull and all of the other sensations he has been experiencing fade away; and he is left, as it were, floating in darkness, isolated, but fully conscious and able to contemplate his isolated situation ...
Here is another wrong prediction: if dualism were correct, we should expect that the ingestion of large quantities of alcohol would result in a partial or complete loss of motor control but leave the mind clear.”
The duplication argument (pp. 180-182).

How do you think that a dualist like Swinburne should respond?