I have no very firm ontological beliefs. I don't want to make any claim about whether fictional characters or mathematical abstractions "really exist".
I do claim that I can talk about abstractions without there being any set of physical referents for that abstraction. I think it's utterly routine to write software that manipulates things without physical referents. A type-checker, for instance, isn't making claims about the contents of memory; it's making higher-order claims about how those values will be used across all possible program executions -- including ones that can't physically happen.
I would cheerfully agree with you that the cognitive process (or program execution) is carried out by physical processes. Of course. But the subject of that process isn't the mechanism. There's nothing very strange about this, as far as I can tell. It's routine for programs and programmers to talk about "infinite lists"; obviously there is no such thing in the physical world, but it is a very useful abstraction.
By the way, I think your Bugs Bunny example fails. When I talk to somebody about Bugs Bunny, I am able to make myself understood. The other person and I are able to talk, in every sense that matters, about the same thing. But we don't share the same mental states. Conversely, my mental picture isn't isomorphic to any particular set of photons; it's a composite. Somehow, that doesn't defeat practical communication.
The case might be clearer for purely literary characters. When I talk about the character King Lear, I certainly am not saying something about the physical copy I read! Consider the perfectly ordinary (and true) sentence "King Lear had three daughters." That's not a claim about ink, it's a claim about the mental models created in competent speakers of English by the work (which itself is an abstraction, not a physical thing). Those models are physically embodied, but they are not physical things! There's no set of quarks you can point to and say "there's the mental model."
mental models created in competent speakers of English by the work (which itself is an abstraction, not a physical thing)
This is where we disagree. Those mental models are simply arrangements of matter. The fact that it feels like you're referring something separate from an arrangement of matter-memory in your brain is another thing all together. The reason that practical communication works at all is that there is an extreme amount of mutual information held between the set of features which you use to categorize the physical memory of, say, Bugs Bunn...
I aim to make several arguments in the post that we can make statements about what should be done and what should not be done that cannot be reduced, by definition, to statements about the physical world.
A Naive Argument
Lukeprog says this in one of his posts:
I would like to question that statement. I would guess that lukeprog's chief subject of interest is figuring out what to do with the options presented to him. His interest is, therefore, in figuring out what he ought to do.
Consider the reasoning process that takes him from observations about the world to actions. He sees something, and then thinks, and then thinks some more, and then decides. Moreover, he can, if he chooses, express every step of this reasoning process in words. Does he really lose interest at the last step?
My goal here is to get people to feel the intuition that "I ought to do X" means something, and that thing is not "I think I ought to do X" or "I would think that I ought to do X if I were smarter and some other stuff".
(If you don't, I'm not sure what to do.)
People who do feel that intuition run into trouble. This is because "I ought to do X' does not refer to anything that exists. How can you make a statement that doesn't refer to anything that exists?
I've done it, and my reasoning process is still intact, and nothing has blown up. Everything seems to be fine. No one has explained to me what isn't fine about this.
Since it's intuitive, why would you not want to do it that way?
(You can argue that certain words, for certain people, do not refer to what one ought to do. But it's a different matter to suggest that no word refers to what one ought to do beyond facts about what is.)
A Flatland Argument
"I'm not interested in words, I'm interested in things. Words are just sequences of sounds or images. There's no way a sequence of arbitrary symbols could imply another sequence, or inform a decision."
"I understand how logical definitions work. I can see how, from a small set of axioms, you can derive a large number of interesting facts. But I'm not interested in words without definitions. What does "That thing, over there?" mean? Taboo finger-pointing."
"You can make statements about observations, that much is obvious. You can even talk about patterns in observations, like "the sun rises in the morning". But I don't understand your claim that there's no chocolate cake at the center of the sun. Is it about something you can see? If not, I'm not interested."
"Claims about the past make perfect sense, but I don't understand what you mean when you say something is going to happen. Sure, I see that chair, and I remember seeing the chair in the past, but what do you mean that the chair will still be there tomorrow? Taboo "will"."
Not every set of claims is reducible to every other set of claims. There is nothing special about the set "claims about the state of the world, including one's place in it and ability to affect it." If you add, however, ought-claims, then you will get a very special set - the set of all information you need to make correct decisions.
I can't see a reason to make claims that aren't reducible, by definition, to that.
The Bootstrapping Trick
Suppose an AI wants to find out what Bob means when he says "water'. AI could ask him if various items were and were not water. But Bob might get temporarily confused in any number of ways - he could mix up his words, he could hallucinate, or anything else. So the AI decides instead to wait. The AI will give Bob time, and everything else he needs, to make the decision. In this way, by giving Bob all the abilities he needs to replicate his abstract concept of a process that decides if something is or is not "water", the AI can duplicate this process.
The following statement is true:
But this is certainly not the definition of water! Imagine if Bob used this criterion to evaluate what was and was not water. He would suffer from an infinite regress. The definition of water is something else. The statement "This is water" reduces to a set of facts about this, not a set of facts about this and Bob's head.
The extension to morality should be obvious.
What one is forced to do by this argument, if one wants to speak only in physical statements, is to say that "should" has a really, really long definition that incorporates all components of human value. When a simple word has a really, really long definition, we should worry that something is up.
Well, why does it have a long definition? It has a long definition because that's what we believe is important. To say that people who use (in this sense) "should" to mean different things just disagree about definitions is to paper over and cover up the fact that they disagree about what's important.
What do I care about?
In this essay I talk about what I believe about rather than what I care about. What I care about seems like an entirely emotional question to me. I cannot Shut Up And Multiply about what I care about. If I do, in fact, Shut Up and Multiply, then it is because I believe that doing so is right. Suppose I believe that my future emotions will follow multiplication. I would have to, then, believe that I am going to self-modify into someone who multiplies. I would only do this because of a belief that doing so is right.
Belief and logical reasoning are an important part of how people on lesswrong think about morality, and I don't see how to incorporate them into a metaethics based not on beliefs, but on caring.