Let me have another go at this, since I've now rewritten the is-ought section of 'Pluralistic Moral Reductionism' (PMR).

This time around, I was more clear that of course it's true that, as you say:

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

We can make reducible 'ought' statements. We can make irreducible 'ought' statements. We can exhibit non-cognitive (non-asserting) verbal behaviors employing the sound 'ought'.

For the purposes of the PMR post, I'm interested to investigate frameworks that allow us to determine whether a certain subset of 'ought' statements are true or false.

Thus, in the context of PMR, non-asserting verbal behaviors employing 'ought' sounds are simply a different subject matter. They do not belong to the subset of 'ought' statements I am investigating for that particular post. (I discussed this in the cognitivism vs. non-cognitivism section.) At the same time, clearly such statements can be useful. For example, you can use them to affect others' behavior. You can affect others' behavior and attitudes with non-asserting verbal behaviors, such as when you say "female circumcisions" with a gasp and a frown.

Also in the context of PMR, some 'ought' statements can quickly be tossed in the 'false' bin, because the speaker uses 'ought' language assertively to refer to things that clearly don't exist, like divine commands.

In the context of PMR, other 'ought' statements can be tossed into the 'false' bin if you are a physicalist, because the speaker uses 'ought' language assertively to refer to things that don't fit within a physicalist ontology, like non-natural moral properties. If you're not a physicalist, then our debate about such 'ought' statements can shift to a debate about physicalism vs. non-physicalism.

Will, you seem to be saying that 'ought' has only one meaning, or one definition. You also seem to be saying that this one meaning of 'ought' (or 'should') is captured by what we 'actually want' in the CEV sense. Is that right so far?

If so, I'm still not clear on your arguments for this conclusion. Your writing here has a very high ratio of unstated premises to stated premises. My own writing does that all the time for communication efficiency, in the hopes that my unstated premises are shared or else successfully inferred. But many times I find that the unstated premises didn't make it into the other's mind, and thus my enthymeme is unclear to it. And when I care enough about my argument being clear to certain people, I take the time to draw my unstated premises into the light and state them explicitly.

Since I'm having trouble guessing at the unstated premises in your arguments for singularism about the meaning of 'should' or 'ought', I'll request that you state them explicitly. Would you please state your most central argument for this singularism, without unstated premises?