Locke’s chapter on personal identity is a masterpiece. Nonetheless, it is long, frequently repetitive, occasionally digressive, and, in a few places, downright confusing.
To help you find the most important parts and avoid the pitfalls, I summarized the central point of each section.
The very most essential sections are: §§3–4, §§6–7, §§9–12, §§14–16, §§19–20, and §22. You should feel confident that you understand those.
We are going to talk about how Locke thinks about identity in general. We will get to personal identity in earnest next time.
§1. How do you ask a question about identity? Locke’s answer is that questions about identity involve comparing things at different times.
He asserts that two things of the same kind cannot be in the same place at the same time. Then he draws two conclusions from this principle. (i) One thing cannot have two beginnings.1 (ii) Two things of the same kind cannot have one beginning.
§2. Assertion that there are only three substances: (1) God, (2) finite intelligences (or “spirits”), (3) bodies. Each has a single beginning, so there is no doubt about the identity of God, finite intelligences (see note), or atoms (meaning the smallest particles of matter).2
The different substances do not exclude one another from occupying a space at a particular time, although they do exclude other members of the same kind of substance. Thus matter and mind can be in the same place at the same time; your brain and your mind are in the same place at the same time, for instance. But there cannot be different pieces of matter in the same place at the same time.
§3. Extension of these points about the identity of simple things, like atoms, to complex things, like masses of matter, plants, and animals. Locke claims that two different complex things can occupy the same place at the same time. So when you ask whether a complex thing has remained the same over time, you need to specify what kind of thing you are asking about.
As an illustration, Locke distinguishes between a mass of matter and a living thing. Whenever you point at a horse or a tree, you are pointing at both a mass of matter and a living thing. When a colt becomes a horse, or a sapling becomes a mighty oak, the mass of matter changes but the animal or plant remains the same. So the identity of the living thing is not the same as the identity of a mass of matter.
§4. Locke claims that the identity of a living thing consists in the organization of the thing’s parts to continue its life.
§5. Analogy between living things and machines. In both cases, the identity of the thing consists in having its parts organized so that it will continue to function. They differ because machines are driven by an external “force” while the motion of living things has internal causes.
Locke draws a distinction between person and man. A man is a human animal. A person is a thinking thing (see §9). You would think that these are just two ways of identifying the same thing, but Locke disagrees.
§6. Definition of the term “man” to mean a human animal. Locke appears to argue for this with examples. But he is really just stating that this is how he will use the word “man.”
§7. What is the question about personal identity? There are three kinds of thing: substance, man, and person. The question is whether the identity of one of them consists in the identity of the other. So we are going to talk about questions like the following. Does being the same man (human animal) over time consist in being the same substance over time? Does being the same person over time consist in being the same man over time? Does being the same person over time consist in being the same substance over time? (The substances would be either finite spirits or material bodies; see §2.)
§8. Reiterating the definition of “man” as a human animal. Locke quotes a long story about a parrot in order to show that the word “man” refers to a human animal. The parrot has the qualities sometimes thought to be characteristic of human beings: it is rational and uses language. But it has a parrot’s body and so, according to Locke, it cannot be a man. As in §6, Locke is more insisting on a definition than he is proving a point.
§9. Definition of the term “person.” A person, according to Locke, “is a thinking intelligent being that has reason and reflection, and can consider itself as itself, the same thinking thing in different times and places.” A person considers itself as itself by being conscious of its thoughts and experiences. A person is conscious of its thoughts and experiences by being aware of having them.
We use consciousness to distinguish our own thoughts and experiences from those that belong to others: I am aware of my thoughts and experiences in a way that I am not aware of yours. We also use consciousness to determine how we are related to people in the past. If I can remember having the thoughts and experiences of a person in the past, I am identical with the past person. If I cannot, then we are different people. When Locke talks about extending consciousness “backwards,” he means remembering.