It is not necessary that whilst I live I live happily; but it is necessary that so long as I live I should live honourably.

A categorical imperative would be one which represented an action as objectively necessary in itself, without reference to any other purpose.

Live your life as though your every act were to become a universal law.

That Logic has advanced in this sure course, even from the earliest times, is apparent from the fact that, since Aristotle, it has been unable to advance a step, and thus to all appearance has reached its completion.

To be is to do.

Always recognize that human individuals are ends, and do not use them as means to your end.