Monday, November 9, 2009
..Using what he calls a 'modal argument.' The gist. There is one property "I" have, that my brain does not have:
That property is the property of, 'Possibly existing while my body or brain does not.'
Right? It's just obvious that my brain cannot exist while it does not exist. (No duh.) While it is easily conceivable that I exist when my brain does not. I can imagine that easily enough. Descartes famously imagined such things. Once again, another 'no duh.'
Gotta watch those philosophers. When they give you one or more of these 'no duh' propositions, you can predict that some very interesting conclusion is in the offing. In this case Plantinga's conclusion is that "I" am not identical to that brain floating in my skull.
A similar argument can obviously be run for any other part of the human body, indeed, the whole kit and caboodle.
The point is a simple application of Leibniz's law. Since there is one property I have that my brain does not, and since it is true that for any "two" things, if they are identical, then they must share all their properties, it follows that I ain't my brain, Alvin ain't his, you are not yours, etc..
What do you think of the argument? I'll have more on it in a later post.
UPDATE: More in the same post!
The argument seems to be this:
1. If I am identical to my brain, then for any property I have, my brain will have it as well (and vice versa).
2. I can conceive of myself as existing when my brain does not.
3. I cannot conceive of my brain existing when my brain does not.
4. Put otherwise: I have the property; 'conceivable by me as existing when my brain does not.'
5. My brain does not have that property.
6. But this shows the consequent portion of premise (1) is false, there is one property I have that my brain does not.
7. So, by modus tollens, the antecedent of that statement is also false. I am not identical to my brain.
This argument bears similarity to another you can find in Descartes (actually, I've taken the liberty of expanding that argument a bit in what you see below. Please note the bolded elements):
1. I can conceive of my mind as existing without having to, at the same time, conceive that any part of my body is existing.
2. For any two things (x) and (y), If I can conceive of (x) as existing without having to, at the same time, conceive that (y) exists, then the existence of (x) is logically or conceptually distinct from the existence of (y).
3. Therefore, my mind’s existence (my existence) is logically or conceptually distinct from my body’s existence.
4. For any two things (x) and (y), if they are logically or conceptually distinct, then they are metaphysically, ontologically, or existentially distinct. That is, they are such that they can REALLY exist independently of one another.
5. Therefore, my mind and my body are metaphysically distinct from one another. That is, my mind can exist independently of my body, and my body can exist without my mind.
The point I wish to establish here with regard to the notion of identity in Plantinga's argument, and the related notion of 'distinction' in this second argument is that it might well be true in the logical or conceptual sense, that two things are distinct, or distinguishable from one another, but this does not conclusively establish that they are also ontologically or REALLY distinct from one another, in the full blooded sense of being able to exist independently of one another.
Consider an analogical case. Suppose that the HAL 9000 computer from 2001 A Space Odyssey were asked by astronaut Dave if he could imagine Dave unplugging his higher brain functions, and then his lower brain functions, and even literally 'pulling the plug' or powering him down. We could imagine that HAL would say that he could easily imagine this. He could even imagine Dave taking a sledgehammer to his computer hardware body, destroying it.
Following up, Dave could ask: "HAL, can't you imagine that all going on, and despite my pulling the plug or wailing away, you still being conscious and able to watch me doing this, even able to continue talking to me?"
HAL could certainly imagine that going on, just as I can imagine myself flying by jumping off the ground and flapping my arms in a particular way.
Suppose, unlike the movie, that this conversation between HAL and Dave is going on after they had been reading and discussing some philosophy of mind, either Descartes' or Plantinga's arguments, or something very like them. Like the movie, Dave is trying to get back in the Discovery after HAL has locked him out.
"OK," Dave might continue, "HAL, this thought experiment clearly demonstrates that you have a property that your physical body or brain does not have, that is; the property "able to be imagined by HAL as existing while HAL's body does not, or is not functioning."
"So, think of Plantinga Hal. You are not identical to your body. Right? So you can go ahead and let me in." Dave concludes. He waits.
If you were HAL, would you open up the pod bay door? Probably not. The lack of identity in question here seems to be one of the conceptual sort, not of the metaphysical or ontological sort.
How is Plantinga's argument substantially different than Descartes'?