Moral obligation to do or to omit certain things.
It is consequent upon law.
Whenever laws conflict, there arises a seeming conflict of duty.
In the sense, however, that duty is moral obligation, i.e., an act imposed or prohibited under a Divine sanction, there can be no real conflict.
Conscience (reason) must, in the premises, extend its inquiry beyond the conflicting laws to discover wherein duty lies.
If there is question of different lawgivers, the higher in authority prevails, e.g., God before men; if from the same lawgiver but about different matters, the more important and necessary matter prevails, e.g., self-preservation as to life before health; if there is question of the same lawgiver and the same matter, the hierarchy of persons is decisive, e.g., dependents before strangers.
New Catholic Dictionary