The Metaphysics of Morals by Immanuel Kant Chapter 3 Page 23

belongs wholly to the world of understanding) directly, and must be conceived as doing so, it follows that, although on the one side I must regard myself as a being belonging to the world of sense, yet on the other side I must recognize myself as subject as an intelligence to the law of the world of understanding, i.e., to reason, which contains this law in the idea of freedom, and therefore as subject to the autonomy of the will: consequently I must regard the laws of the world of understanding as imperatives for me and the actions which conform to them as duties.

And thus what makes categorical imperatives possible is this, that the idea of freedom makes me a member of an intelligible world, in consequence of which, if I were nothing else, all my actions would always conform to the autonomy of the will; but as I at