A term coined by Immanuel Kant to characterize the moral law as thus enunciated:
"Act so as to use humanity, in your own person or in others, always as an end, and never merely as a means."
It is enacted by reason alone, is the sole motive of the will, an absolute imperative through mere respect for reason dictating its universality and necessity as based on humanity itself.
It is a law unto itself, autonomous, and subject to no external lawgiver.
Morality consists solely in obedience to this law of reason and in acting solely through respect for reason as a law.
In criticism it is affirmed that man is not an end in himself but is subordinate to God as his ultimate end; nor is he autonomous, but is subject to God as his supreme Lord and Lawgiver.
Reason does not enact the moral law but merely recognizes and proclaims it.
It is of wider extension than the merely obligatory.
The basis of morality is God as the ultimate end, highest good, and supreme lawgiver.
New Catholic Dictionary