supererogatory \soo-puhr-ih-ROG-uh-tor-ee\, adjective:
1. Going beyond what is required or expected.
2. Superfluous; unnecessary.
As a result, Crane's moral reflections range from the pre-ethical (duties toward animals) to the properly ethical (conduct toward humans in ordinary situations) to the optional and supererogatory (heroic actions above and beyond ethical obligation).
-- Patrick K. Dooley, "The humanism of Stephen Crane", The Humanist, January 11, 1996