This is our first day on metaphysics. Our first metaphysical question is: what are the necessary and sufficient conditions of identity? Specifically, we’re interested in the identity of persons
We discussed the first half of Locke’s chapter on “Identity and Diversity.” This covered Locke’s views about identity in general, the identity of masses of matter, the identity of living things like plants and animals, and his initial statement of his view about the identity of persons.
The position Locke is driving towards is that the conditions for the identity of a person are different from the conditions for the identity of masses of matters, animal lives, or immaterial souls.
I highly recommend looking at the outline I posted. It gives summaries of what Locke was saying in each section and identifies the sections that I believe are especially important for understanding his view.
It’s not easy to formulate questions about identity properly. Suppose you ask “What is involved in one’s thing being identical with another?” The appropriate answer is: nothing. One thing can’t be identical with something else. Or suppose you ask “what is involved in one thing’s being identical with itself?” Here, it’s hard to understand why there is a question. If I knew what the thing we were talking about was, I would pretty much have my answer. And if I didn’t know what we were talking about, we wouldn’t be able to get started.
Locke deftly handles this problem in the first sentence. He notes that questions about the identity of things can be posed over time: is this thing now the same as that thing then? That lets us formulate a sensible question. It also enables us to talk about change (since change happens over time). Many questions about identity concern what changes a thing can undergo while remaining the same. Suppose, for example, we asked what changes the table could survive while remaining the same. Then we would start going through possible changes. The table will remain the same table if you paint it a different color: it can ‘survive’ a change in color while remaining the same table. But it can’t survive being smashed up. And so on.
A helpful distinction for talking about identity through change is the distinction between qualitative and numerical identity. The idea that things can continue to be the same despite changes is the idea that they can undergo qualitative change while remaining numerically the same.
Two things are qualitatively identical if all their qualities are the same. Strictly speaking, we should say something like “all their intrinsic qualities are the same.” Why the qualification? Well, you could have two balls sitting side by side that would have exactly the same qualities except for one: their spatial position. The point is that the two balls themselves are exactly alike: if you turned around and I switched them, you wouldn’t be able to tell them apart. That’s what I mean in calling them qualitatively identical.
The example also illustrates numerical identity. There are two balls. Even though they are qualitatively identical, they are numerically distinct. You could destroy one and the other would remain intact.
This is going to be important when we talk about people down the line. Would someone who has all of your thoughts and memories be numerically identical with you or merely qualitatively identical?
Another nice thing that Locke insists on is the need to be specific about what kind of thing you’re asking about. Say you point at the oak tree outside Pearsons Hall and ask: “is this now the same as the thing that was on the same spot ten years ago?”
That question is not specific enough because there are at least two things you might be asking about: the mass of matter and the living tree.
It’s not the same mass of matter that was on the spot ten years ago because the matter that makes up the tree is different now than it was ten years ago. The tree is bigger and it has lost leaves and branches.
It is the same tree as the one that was on the spot ten years ago, however. What makes it the same tree? Locke has an answer. There has been one “continued organization” over the past ten years that has received and distributed nourishment in a way that continues the life of the tree (see §4).
We’re going to be talking about necessary and sufficient conditions for identity over time.
A necessary condition of a thing’s identity over time is a condition that must be met for a thing at one point in time to be numerically identical with a thing at another point in time.
A sufficient condition of a thing’s identity over time is a condition that, when it is met, guarantees that a thing at one point in time is numerically identical with a thing at another point in time
It’s really difficult to come up with examples that illustrate the difference between necessary and sufficient conditions of identity. But I can illustrate the difference between necessary and sufficient conditions in general.
Having a color is a necessary condition of being brown. Nothing could be brown without having a color. Conversely, being brown is a sufficient condition of having a color. Everything that is brown has a color.
This is brown and it has a color. By itself, that doesn’t prove much. But if you wanted to show that having a color is not a necessary condition of being brown, or if you wanted to show that being brown is not a sufficient condition of having a color, you would have to give an example of something brown that did not have a color. Good luck with that!
Of course, having a color is not a sufficient condition of being brown. This box has a color and it is not brown; it is green. That proves that having a color is not sufficient for being brown.
It also proves that being brown is not a necessary condition of having a color. The box has a color and it is green, not brown. So being brown cannot be a necessary condition of having a color.
Here is another example. Suppose the Cardinals are playing the Red Sox in the World Series. The first team to win four games wins the series. Suppose the Red Sox have won the first three games.
Winning the fourth game is a sufficient but not a necessary condition of the Red Sox winning the World Series.
It is sufficient because winning the fourth game means they win four games and that would guarantee that they win the World Series.
It is not a necessary condition of winning the World Series because they could still do that by winning the fifth game even if they lose the fourth game.
Winning the fourth game is a necessary but not sufficient condition of the Cardinals winning the World Series.
It is a necessary condition because if the Cardinals lose the fourth game, the Red Sox would have won four games, thereby winning the series. So the only way the Cardinals can win the series is if they win the fourth game.
It is not a sufficient condition because they would still have to win three more games in order to win the series: the fifth, sixth, and seventh games.
And what does this have to do with personal identity? Well, Locke is going to consider a variety of proposals about what personal identity over time consists in. These can be put in terms of necessary and sufficient conditions.
For instance, suppose you said that personal identity over time consists in the identity of a mass of physical matter. Then you would be saying:
A necessary condition of A being the same person as B is that A and B are the same mass of matter.
A sufficient condition of A being the same person as B is that A and B are the same mass of matter.
This way of putting things helps us to identify the ways that one could go about challenging a proposal like this. For instance, someone would probably say that the necessary condition is false on the grounds that I am the same person as the one who went to lunch two hours ago even though I am a different mass of matter than that person was. After all, my current mass includes what I ate for lunch.
Is being the same mass of matter a sufficient condition of being the same person as me? Probably not. After I’m dead, my matter will be dispersed throughout the environment. It will inevitably wind up in plants and other animals. Suppose that, after billions of years, all of the atoms that made up my body at my death wind up composing someone else’s body. Given enough time, almost anything can happen, right? Anyway, the future person would have the same mass of matter as I do, but would not be the same person as me. So having the same mass of matter as me cannot be a sufficient condition of being the same person as me. At least, that’s what I think.
Granted, this is a silly proposal. No one thinks that personal identity consists in the identity of a mass of matter. But it does illustrate the more serious proposals that we will take up next time, namely, that personal identity consists in being the same living human animal (“man,” in Locke’s lingo) or that personal identity consists in having the same immaterial spirit or soul.