Apart from warlike activity proper, the institution of the duel is also an expression of the same superior readiness for combat; and the duel is a leisure-class institution. The duel is in substance a more or less deliberate resort to a fight as a final settlement of a difference of opinion. In civilized communities it prevails as a normal phenomenon only where there is an hereditary leisure class, and almost exclusively among that class. The exceptions are (1) military and naval officers who are ordinarily members of the leisure class, and who are at the same time specially trained to predatory habits of mind and (2) the lower-class delinquents -- who are by inheritance, or training, or both, of a similarly predatory disposition and habit. It is only the high-bred gentleman and the rowdy that normally resort to blows as the universal solvent of differences of opinion. The plain man will ordinarily fight only when excessive momentary irritation or alcoholic exaltation act to inhibit the more complex habits of response to the stimuli that make for provocation. He is then thrown back upon the simpler, less differentiated forms of the instinct of self-assertion; that is to say, he reverts temporarily and without reflection to an archaic habit of mind.
This institution of the duel as a mode of finally settling disputes and serious questions of precedence shades off into the obligatory, unprovoked private fight, as a social obligation due to one's good repute. As a leisure-class usage of this kind we have, particularly, that bizarre survival of bellicose chivalry, the German student duel. In the lower or spurious leisure class of the delinquents there is in all countries a similar, though less formal, social obligation incumbent on the rowdy to assert his manhood in unprovoked combat with his fellows. And spreading through all grades of society, a similar usage prevails among the boys of the community. The boy usually knows to nicety, from day to day, how he and his associates grade in respect of relative fighting capacity; and in the community of boys there is ordinarily no secure basis of reputability for any one who, by exception, will not or can not fight on invitation.