"A free will and a will under moral laws are the same": Kant’s concept of autonomy and his thesis of analyticity in Groundwork III

In section 1 of GMS III, Kant claims that “a free will and a will under
moral laws are the same” (447.6–10). 1 h is claim expresses Kant’s concept
of autonomy; after all, the concept of freedom is the “key” (446.6) to
this concept. So if we understand freedom in its relation to morality, we
understand autonomy. But how are we to understand this relation? On
the standard reading, Kant’s claim is that a free will is under the moral
law as a Categorical Imperative (CI); hence, once it is shown that we are
free it is shown that we are obliged by the CI. 2 h is interpretation, I will
argue, is incorrect.