Suppose that there were a device like the teletransporter (a.k.a. “transporter”) on Star Trek. To quote from Wikipedia:
A transporter is a fictional teleportation machine used in the Star Trek science fiction franchise. Transporters allow for teleportation by converting a person or object into an energy pattern (a process called “dematerialization”), then sending (“beaming”) it to a target location or else returning it to the transporter, where it is reconverted into matter (“rematerialization”).
Now suppose that someone modifies it. Instead of being dematerialized, someone in the machine is just scanned. Then the information from the scan is beamed to from Earth to Mars to create a material body there while the person who got in the transporter on Earth is left intact.
Most of us say that the dematerializing version of teletransportation is a way of traveling: you get in the machine, get dematerialized, beam to Mars, and then get rematerialized. You moved from Earth to Mars.
However, most of us also say that in the modified version, where you are just scanned without being dematerialized, you remain on Earth while the person on Mars is a copy. You did not travel this time, even though the beaming and rematerializing steps are the same.
This pair of examples convinces Parfit that identity is not what matters for survival. To put it another way, you can survive into the future even if no one in the future is the same person as you.
And yes, that sounds paradoxical, but the reasoning is fairly compelling.
There is a lot of vocabulary in the reading that makes it harder than it probably should be. But do not fear. I am here for you.
Qualitative and numerical identity (201-202). Two things can have the same qualities while being, well, two different things. Two identical billiard balls are qualitatively identical but numerically different. By the same token, the person on Mars is qualitatively identical with the person on earth, at least initially. But it does not follow that they are numerically identical.
The physical and psychological criteria of personal identity (202-209). These are two contending views about personal identity over time. The physical criterion holds that A is the same person as B if and only if A and B have the same body. (Strictly speaking, the same brain.) The psychological criterion holds that they are the same if and only if they are psychologically continuous with one another: there are overlapping psychological connections, such as memories, intentions, beliefs, desires, character traits, and so on linking them. The physical criterion holds that a person is what Locke calls a “man” whereas the psychological criterion is a modified version of Locke’s basic idea about what a person is.
Reductionism and non-reductionism (209-14). This is a lot more complicated than it needs to be. Parfit is going to dispute the idea that there are always determinate answers to questions about personal identity. We will go into what that means in class, but the basic idea is that when you ask “Is A the same person as B?” someone who believes that there must be a determinate answer thinks that there are only two possible answers: yes or no. There is no third alternative such as “a little of both” or “there is no saying.”
There would be determinate answers to questions about personal identity if personal identity consisted in the identity of an indivisible immaterial soul (a.ka. a “separately existing entity”). We would look at A’s soul and see if B has the same one. If the souls are the same, the answer to the question “is A the same person as B?” would be “yes.” If the souls are different, the answer is “no.” There is no third possibility.
Parfit does not believe there are indivisible immaterial souls. That leaves physical bodies or psychological connections as the remaining bases for personal identity. However, Parfit is going to argue, neither one guarantees that the question “is A the same person as B?” will always have a determinate “yes” or “no” answer.
That is the essence of what he is getting at. The labels “non-reductionist” and “reductionist” hinder more than they help, in my opinion. They refer to people who think that all questions about personal identity either do or do not have determinate yes or no answers. Non-reductionists think the answers are always yes or no while reductionists disagree. That is the important part.
Here are the weedy details that, in my opinion, are less important. All non-reductionists believe that questions about personal identity have to have determinate yes or no answers. Some of them believe that this is so because people are made up of indivisible immaterial souls while others think it is so because physical or psychological relations always yield definite yes or no answers. Parfit is going to argue that those who believe that physical or psychological relations always yield definite yes or no answers to questions about personal identity are mistaken. They are logically committed to reductionism even if they think they are non-reductionists.
Do not worry if that makes your head spin. The distinction between reductionism and non-reductionism is more confusing than helpful. So I would not spend a lot of time trying to figure it out if I were you.
At the end of the reading, Parfit talks a lot about something he calls “what matters” (215-17). What he means is probably better expressed by adding a couple words: what matters for survival? That is, what has to be true in order for me to survive into the future?
Most of us think that what has to be true is that I will be identical with someone living in the future. To put it another way, what matters for my survival is that a future person will be the same person as me. What else could it mean, right?
Parfit is going to deny this. He thinks that what matters for my survival is that there is someone in the future who is psychologically connected or psychological continuous with me (see “Relation R” on p. 215).
What’s the difference? Well, in the Branch-Line case, there are two people who are psychologically connected or continuous with you before you got into the machine: one is on Earth and the other is on Mars.
When you read the story, you think that you are the one on Earth and that the person on Mars is a copy. Parfit thinks that is an illusion. The relationship between you before you got into the machine and the person on Earth is the same as the relationship between you before you got in the machine and the person on Mars. You can survive as either one of them. Or even both!
The reason why is that there is nothing extra to being you beyond the continuation of your psychology. There is no immaterial soul, for instance, that makes up your essence. There is just the various elements of your psychology. As long as they continue, so do you. Whether they continue in one person, two, three, or four is irrelevant.