Immanuel Kant 
The Metaphysical Elements of Ethics 

Ethics in ancient times signified moral philosophy (philosophia moralis) generally, which was also called the doctrine of duties. Subsequently it was found advisable to confine this name to a part of moral philosophy, namely, to the doctrine of duties which are not subject to external laws (for which in German the name Tugendlehre was found suitable). Thus the system of general deontology is divided into that of jurisprudence (jurisprudentia), which is capable of external laws, and of ethics, which is not thus capable, and we may let this division stand.