The substance objection
The substance objection
The objection is fairly straightforward: Locke defines a person as a thinking, intelligent thing. What is the thing that thinks other than a human animal (man) or immaterial substance (soul)?
But if my substance is a thinking thing, then my substance is a person: the person that is me. So in order to remain the same person over time, I have to remain the same substance. You can find both Butler and Reid making this point.
Locke's analogy with animal life
Locke himself concedes that thinking depends on substances: without an immaterial substance or animal life (he's agnostic regarding which of the two is necessary for consciousness) there's no thinking, so, all thinking takes place in some substance or other.
But Locke wants to insist that the conscious being can continue to exist despite changes in the underlying, (apparently) thinking substance. To make the point, he will appeal to an analogy with animal life.
I don't think anyone has any trouble with saying that a person could be made up of different bits of material substance: most of us gain and lose matter all the time but no one would suggest that we thereby become different persons.
Locke thinks the same is true of immaterial substance: is it conceivable that you've had several different souls during your lifetime? Since you wouldn't have noticed the change, according to Locke, it is.
Consciousness is what personal identity consists in. I am the person that I am at a moment in time by virtue of having conscious thoughts and experiences at that moment in time. I am the same as a person at another point in time by virtue of (being able to?) extend my consciousness now to his experiences.
Consciousness, according to Locke, unites these different moments into a person, much as life organizes matter into an animal.
The hardest thing to understand about Locke's position: Locke is willing to admit that consciousness requires an underlying substance, such as a brain or an immaterial soul, but he denies that you have to have the same chunk of immaterial soul stuff or the same material brain in order to be the same conscious being or person.
Why is consciousness important for Locke?
Locke's analogy is good as far as it goes. But it doesn't really meet the substance objection head on. It just asserts that there must be a way for a conscious being to remain the same over time despite material or immaterial changes just as there is some way that animals remain the same over time despite material changes.
Of course, Butler and Reid won't buy that: they don't think that, strictly speaking, animals and plants do remain the same despite material changes. (In all fairness to Locke, that's a pretty tough position they're staking out: my cat dies each time she sheds?)
So, Locke needs to do more than just play defense. He needs to go on offense.
Locke can argue that what he's trying to explain is our concept of a person; what it is that we take ourselves to be and why it's so important to us that, for example, A is the same person as me. Substances have nothing to do with this concept or its apparent importance: as far as we're concerned, substances are completely absent.
Butler and Reid both insist that I have excellent knowledge of my own identity. But how could that be if I was really a substance that I've never seen or had any other empirical evidence of?
Butler and Reid might reply that we know that we are substances because that's the only way we could be thinking beings. Their original argument gives us all that we need for knowledge of substances: I must be a substance for things I know to be true, therefore, I'm a substance. (This strategy is sometimes called a "transcendental argument," by the way).
Common sense objections
Locke's case rests heavily on the contention that he is giving our conception of a person: the one we care about and think is important.
Is that really so? What about sleep or forgetting? Locke may have ways of getting around these phenomena, but they look bad for his theory.
Did Locke blink?
Look at Section 13. Locke seems to be saying that God would never give one thinking, immaterial substance the memories or consciousness of another because that would be unjust: it would give the second substance the rewards or punishments due to the first. (You might also pay close attention to how the Prince moved from his original body into the Cobbler's. He rode along in his soul! See Section 15.)
Oops. That shouldn't matter. Substances aren't persons, remember. So who cares if substance A gets some memories from substance B? Only the memories were supposed to matter, not the substances. How can a substance be punished or rewarded unjustly? You can treat persons unjustly, but not substances.
I think this is a slip on Locke's part. His official position is still that personal identity is distinct from the identity of substances.
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