Condign merit supposes an equality between service and return; it is measured by commutative justice (justitia commutativa), and thus gives a real claim to a reward. Congruous merit, owing to its inadequacy and the lack of intrinsic proportion between the service and the recompense, claims a reward only on the ground of equity. …
The essential difference between meritum de condigno and meritum de congruo is based on the fact that, besides those works which claim a remuneration under pain of violating strict justice (as in contracts between employer and employee, in buying and selling, etc.), there are also other meritorious works which at most are entitled to reward or honour for reasons of equity (ex œquitate) or mere distributive justice (ex iustitia distributiva), as in the case of gratuities and military decorations. From an ethical point of view the difference practically amounts to this that, if the reward due to condign merit be withheld, there is a violation of right and justice and the consequent obligation in conscience to make restitution, while, in the case of congruous merit, to withhold the reward involves no violation of right and no obligation to restore, it being merely an offence against what is fitting or a matter of personal discrimination (acceptio personarum).
