“Act only according to that maxim that you can at the same time will that it should become a universal law; act as if the maxim of your action were to become a universal law of nature” (421).

“Act in such a way that you treat humanity, whether in your own person or in the person of another, always at the same time as an end and never simply as a means” (429).

Act under “idea of the will of every rational being as a will that legislates universal law” (431).
“Act on a maxim which at the same time contains in itself its own universal validity for every rational being” (438). “So act as if your maxims were to serve at the same time as a universal law (for all rational beings)” (438). “Always choose in such a way that in the same volition the maxims of the choice are at the same time present as universal law” (440).

Always regard yourself “as legislator in a kingdom of ends rendered possible by freedom of the will, whether as member or as sovereign” (434).
“Act in accordance with the maxims of a member legislating universal laws for a merely possible kingdom of ends” (439).