The Metaphysical Elements of Ethics by Immanuel Kant Chapter 3 Page 1

Of the Reason for conceiving an End which is also a Duty

An end is an object of the free elective will, the idea of which determines this will to an action by which the object is produced. Accordingly every action has its end, and as no one can have an end without himself making the object of his elective will his end, hence to have some end of actions is an act of the freedom of the agent, not an affect of physical nature. Now, since this act which determines an end is a practical principle which commands not the means (therefore not conditionally) but the end itself (therefore unconditionally), hence it is a categorical imperative of pure practical reason and one, therefore, which combines a concept of duty with that of an end in general.

Now there must be such an end and a categorical