[woodruffw]

> In my mind, Kant's categorical imperative could be viewed as either a proposed definition of the good (in which case Moore's argument is applicable), or a claim about what actually is good (in which case it escape's Moore's argument)

It’s an academic opinion, but I believe it’s the latter: the very first line in the GMS asserts that the metaethical object itself is the good will: “nothing in the world (or indeed beyond it) can possibly be conceived as good without qualification except for the Good Will.”

The CI is the logical consequence (according to Kant) of what the good is. But that distinction is definitely subtle in the context of his normative ethics.