How is a categorical imperative possible? : Kant’s deduction of the categorical imperative (GMS, III,4)

Kant’s deduction of the categorical imperative is the answer to the following
question: “How is a categorical imperative possible?” The answer
is given in subsection 4 (Sec. 4) of chapter three of the Groundwork.
It is impossible to understand this answer, and hence impossible
to understand Kant’s deduction of the moral law, without taking into
account the overall context of Groundwork III (GMS III). However,
here I can only sketch the overall structure of GMS III, and therefore
only present a sketch of what I call Kant’s thesis of analyticity.1 This
thesis is developed in Sec. 1 of GMS III; however, it appears time and
again in GMS III, and it deserves special attention (part 1). Part 2,
then, offers a close reading and analysis of Kant’s deduction.