How exactly does this answer the question?
The set of non-ethical categorical imperatives is non-empty.
I agree. Epistemic imperatives are categorical, but non-empty.
The set of non-ethical hypothetical imperatives is non-empty. Hypothetical imperatives include instrumental rules, you have to use X to achieve Y, game-laying rules, etc.
Right, those are examples where non-ethical hypothetical imperatives often show up.
So how does this add up to a reason to think there is a case against categorical imperatives that doesn’t equally well count against hypothetical imperatives?
So, on your use of ‘end’, an ‘end’ cannot be objective and unconditional? I think that’s a highly uncommon use of the term.
But if you go this way, it seems like it’s less of a reduction of ‘ought’ and more of a misinterpretation, like reducing ‘Santa Claus’-talk into talk about Christmas cheer, or ‘God’-talk into talk of love.
After all, one important constraint on any interpretation of any ‘ought to X’ is that it should be positive towards X as opposed to negative or neutral, in favor of some action or attitude as opposed to against it or indifferent. But a mere predictive causal claim doesn’t have any valence at all: it’s just a neutral claim about what will probably lead to what, without anything positive or negative. So any attempt to reduce oughts to predictive causal claims seems doomed to failure.
EDIT: For the record, I’m an expressivist about normativity, and I think any attempt to understand it in terms of some actual or hypothetical ontology that could serve as the truth-conditions for a descriptive belief is a mistake. The mystery, I would say, lies in a descriptive interpretation of normativity, not in normativity itself.