Full Idea
The moral order expressed in the propositions of duties is just as much part of the fundamental nature of the universe (or any possible universe) as is the spatial or numerical structure expressed in the axioms of geometry or arithmetic.
Clarification
'Axioms' are initial assumptions
Gist of Idea
Moral duties are as fundamental to the universe as the axioms of mathematics
Source
W. David Ross (The Right and the Good [1930], §II)
Book Reference
Ross,W.David: 'The Right and the Good' [OUP 1930], p.29
A Reaction
A few of the axioms of geometry (e.g. the parallel line postulate) have been changed, with interesting results. Moral duties seem to change dramatically in a crisis, such as a war, or a ship sinking. Can I have a duty if I am too dim to perceive it?