Excerpts from "Groundwork for the Metaphysics of Morals"

" There is therefore but one categorical imperative, namely, this:

Act only on that maxim whereby you can at the same time will that it become a universal law"

Second Formulation: "Act as if the maxim of your action were to become by your will a universal law of nature."

Third Formulation: "So act as to treat humanity, whether in your own person or in that of any other, in every case a the same time as an end, never as a means only."

"Now I say: the human being and in general every rational being exists as an end in itself, not merely as a means to be arbitrarily used by this or that will, but in all his actions, whether they concern himself or other rational beings, must be always regarded at the same time as an end...The foundation of this principle is: rational nature exists as an end in itself."

Immanuel Kant