There are at least three kinds of thing sitting in my chair right now:
We know from Locke’s initial remarks about identity that each of these excludes other things of its kind — there’s only room for one mass of matter, one man, and one person — and that each had just one beginning, and so on.
But why don’t they exclude one another? Well, they’re different kinds of things. Proof: an animal can continue to exist even as its mass of matter changes. Or you can have the same mass of matter without having the same animal. If the animal dies there is no longer a “common life” to organize its parts and so there is no animal even though the mass of matter is the same (see §4).
Michael Green, the man, is the same as the man that taught class last week if and only if they are both part of the same animal life. This could be true even if the mass of matter that sat before you today is different than the mass of matter that did so last week.
After all, I did get a haircut in the meantime.
What about the person Michael Green? There was one of those in class last week too. What are the necessary and sufficient conditions of the person who was in class today being the same person as the one with the same name who was in class last week? That’s what the bulk of Locke’s chapter is about.
A minute ago, I wrote “Michael Green, the man, is the same as the man that taught class last week if and only if they are both part of the same animal life.” The “if and only if” part is a quick way of saying that being part of the same animal life as the man that taught class last week is a necessary and sufficient condition of being the same man that taught class last week.
For the fastidious, the “if” is the sufficient condition (if the two are part of the same animal life, then they are the same man), “only if” is the necessary one (if they are the same man, then they are part of the same animal life = they are the same man only if they are part of the same animal life).
We went over necessary and sufficient conditions quickly in class. But most of us need to run over it multiple times. In fact, I’m quadruple checking that previous paragraph right now and I’ve done this more times than I can count. I have a tutorial on them that will probably help.
Our questions about personal identity are questions about the necessary and sufficient conditions of being the same person as some independently identified person.
Locke held that being conscious of A’s thoughts and experiences is a necessary and a sufficient condition of being the same person as A. Someone can be conscious of A’s thoughts and experiences either directly or by remembering them.
We talked about two ways of getting to this position. Locke’s stated reasons are laid out in §§9-10. They concern self-knowledge. As Yavor noted, Locke’s position is quite similar to Descartes’s. Descartes said that he is a thing that thinks and that he had especially intimate knowledge of his own existence based on his thoughts and experiences (see the Second Meditation, for example).
I presented an historical progression of views, from Aquinas’s version of the doctrine that persons are immaterial souls, through Hobbes’s materialism, to Locke’s position. Roughly, Locke disagreed with Aquinas, but in a different way than Hobbes did. He thought that consciousness explains when the little finger is, and when it is not, a part of me.
Locke considered three alternative views. The necessary and sufficient conditions of person A being the same as person B are …
Locke’s reply to the first is that the case of personal identity should not be different than animal or plant identity. A plant may grow while remaining the same plant; that is, it is the same plant despite being a different mass of matter. See §12.
If that’s so, why isn’t something similar true of immaterial substances? Do we know more about the immaterial substances in us than we do about the material ones? Are you more certain that you haven’t inherited Socrates’ soul than you are that you haven’t, ahem, injested, some of the matter that was part of his material body? See §14.
We didn’t cover the last case, but it’s the natural one for a materialist like Hobbes to go for. How does Locke handle it? (Hint: look for the cobbler and the prince).
I want to restrict objections to Locke’s view for Friday. But Charles slipped one in at the end that is just too good to pass up. It is that Locke’s conditions are not transitive while identity is. Specifically, it is possible that:
That can’t be right because if B is the same as A and C is the same as B, then A should be the same as C. Think of it in terms of mathematical equalities. If 2 + 2 = 4 and 3 + 1 = 4, then 3 + 1 = 2 + 2.
This objection was famously given by Thomas Reid in his Essays on the Intellectual Powers of Man (1785).
There is another consequence of this doctrine, which follows no less necessarily, though Mr. Locke probably did not see it. It is, that a man may be, and at the same time not be, the person that did a particular action.
Suppose a brave officer to have been flogged when a boy at school for robbing an orchard, to have taken a standard from the enemy in his first campaign, and to have been made a general in advanced life; suppose, also, which must be admitted to be possible, that, when he took the standard, he was conscious of his having been flogged at school, and that, when made a general, he was conscious of his taking the standard, but had absolutely lost the consciousness of his flogging.
These things being supposed, it follows, from Mr. Locke’s doctrine, that he who was flogged at school is the same person who took the standard, and that he who took the standard is the same person who was made a general. Whence it follows, if there be any truth in logic, that the general is the same person with him who was flogged at school. But the general’s consciousness does not reach so far back as his flogging; therefore, according to Mr. Locke’s doctrine, he is not the person who was flogged. Therefore the general is, and at the same time is not, the same person with him who was flogged at school.
Chart it out. That is, draw three pictures in a line: boy at school, brave officer, and general. Then draw arrows representing memories: which one remembers which one’s experiences? Then note which one is the same person as which, and which is not, according to Locke. You’ll see the problem.