The military meets many of the plausible criteria for being a profession; it differs from professions such as law and medicine, characterized historically solo practitioners with full autonomy. Military organizations are among the most rule-governed social institutions, and the duties of military personnel are typically spelled out explicitly than are the role responsibilities of, say, parents or teachers. The constraints, embodied in the received rules of war, are central to the identity of the military in modern liberal democracies and other regimes that respect international law and, in particular, the law of armed conflict. Ultimately, though, the costs of military forces can be morally justified if they are related in some reasonably clear-cut way to benefits for individual human beings. The motive for ethical behavior to military effectiveness, a functional or instrumental approach does not provide reasons for the warrior to behave well when bad behavior does not seem to have a negative impact on the function of the military.