Thursday, November 29, 2007

An argument against psychological identity theories: accuracy and reliability of copying

According to the psychological identity theorist, if the contents of your mind (e.g., brain or soul) are copied into another mind (brain or soul), with the original mind destroyed, you will survive and come along with the copied contents. Now, plausibly, perfection is not needed in the copying. If one digit in the memory of your phone number is not copied over, and everything else is, then surely you will survive that, if you would survive any such copying operation at all. But some fidelity in copying is needed.

We can measure a copying operation in several ways. For any portion of the information to be copied (think of a 0/1 value or a continuously variable value, for instance), we can talk of the accuracy of the copying, which says how similar is the output of the copying procedure in fact was to the input, and the reliability of the copying, which is a measure of how likely it was that the output would have a given accuracy. (We can come up with various ways of quantifying this, but it doesn't matter.) Now, for a mind-copying to at all plausibly move a person from one mind to another, there has to be both overall accuracy and overall reliability. One won't do without the other. One could, after all, have very high reliability in copying, i.e., a high probability of accuracy, but be unlucky so that the the output is completely unlike the original. The psychological identity theorist would not say the person was moved then, since few of the memories and character traits would have survived. Nor would high accuracy with very low reliability transfer a person. Take a limiting case of low reliability where the output is entirely random and independent of the input. Nonetheless, one might be lucky, with the output by chance being just like the input. That wouldn't result in person-transfer, either. After all, if my mind is destroyed, and completely by chance a man arises randomly after lightning hits a swamp in Transylvania and that many by chance has the same mental states as I did, that man wouldn't be me.

So, we need both high accuracy and high reliability for person-transfer to occur. But now note that reliability is in part an extrinsic criterion. It measures the probability of accuracy. Suppose that you're undergoing a mind-content transfer procedure, and Dr. Black, the evil neurologist, after having starred in Frankfurt's Neurologist, XIII, happens to be sitting around in the lab. Now, almost all of the time when Dr. Black is in a lab when a mind-content procedure takes place, he hijacks the procedure, and ensures that while the subject's original mind is destroyed, the data transfered to the output mind in fact is a very poor copy of the subject--in fact, it is a copy of Dr. Black's vicious mind. This time, however, Dr. Black is distracted, and forgets to hijack the procedure, and only remembers once the operation is done. The reliability of the copying process is very low--Dr. Black was very likely to hijack it.

This leads to the following absurd conclusion. If person-transfer through copying of content is possible, then whether Dr. Black is in the room when the procedure happens determines whether the subject survives the procedure--even if Dr. Black in fact is distracted and in no way causally interacts with the process. Since this absurdity comes from psychological identity theories, we should reject psychological identity theories.

But what if one bites the bullet and says that whether Dr. Black is in the room when the procedure happens does determine whether one survives. Now I have a second move. What happens in copying is a causal process whereby an earlier mind causes a later mind to have the same content. The same thing is happening in us all the time. Our brain's having a certain neural state at t1 (e.g., a state correlated with a belief that 2+2=4) will often cause that brain to have the same state at t2. Our brains are always in a state of flux, and the brain's preserving of information is relevantly very much a process of copying. (Plato says something like this in the Symposium.) Suppose now that you live your ordinary life, but Dr. Black keeps on shadowing you, with his neurological equipment, and he keeps on planning to subvert your brain's data preservation processes, but whenever he is about to do so, by a very small chance, he is distracted and does not. In fact, Dr. Black does not interact with you causally. But his presence makes the reliability of the transmission of data from the past to the future in your mind be very low. By the same reasoning as above, it follows that the mere presence of Dr. Black kills you--even though he in fact does not interact with you.


Mike Almeida said...

Alex, which psy-identity theorists say this?

According to the psychological identity theorist, if the contents of your mind (e.g., brain or soul) are copied into another mind (brain or soul), with the original mind destroyed, you will survive and come along with the copied contents.

Don't these theorists hold that my current psychological states S have to bear the right relation R to my previous psychological states S', in order for me to survive? The relation is typically some sort of causal one. I don't see how a psy-identity theorist could hold that you survive in virtue of being copied, since the "is a copy of" relation is not in general (and not in this case) a causal relation and, further, it cannot ensure numerical identity.

Alexander R Pruss said...

When the copy is made from the original, it counterfactually and causally depends on the original.

Mike Almeida said...

Alex, how? I can't see how the original caused the copy. What caused the agents to copy the original is not that it was there. It was likely some experimental goal or something. I do not deny the counterfactal claim. But I also do not deny the counterfactual claim that had there been no big bang, there would have been no copy. The big bang did not cause the copy, I'd say, any more than the existence of the original did. What am I missing?

Alexander R Pruss said...

Well, there is certainly causal dependence there, and the original state is part of a sufficient set of causes.

Take a simple case of photocopying a sheet of paper. What was on the original paper is a partial cause of what is on the original paper. Why? Well, what was on the original paper is the cause of the fact that light rays bounced off some portions of the paper and not other portions, thereby creating a certain scanned image, which then causally led to the new hard copy.

The same will, I think, be true for any copying method.

And that it is a partial cause doesn't matter, since even in the case of the self-perpetuation of the brain states, it's not just the old brain states alone that give rise to the new ones, but the old brain states plus whatever perpetuation/copyinig machinery there is in the brain, etc.

In any case, the idea of memory transfer seems not to be challenged by psychological identity theorists, though I do not have references off-hand.

Mike Almeida said...


The analogue of the photocopy is the idea (if you will) of the original in the minds of those doing the copying. I don't deny that that (or something like that) is a causal relation. Let me put it this way. Had those doing the copying to have had the idea of the original in mind, and chosen not to copy it (keeping the past and laws the same) it would not have been true that something causally impossible happened. Or, in any case, I have no intuition that something causally impossible would have happened.

Alexander R Pruss said...

I am assuming that the machine doing the copying is scanning the original while impressing the data on the target.