Some philosophers and social scientists have stressed the importance for good government of an altruistic citizenry that values the well being of fellow citizens. Economists, however, have emphasized the need for incentives that induce even the self-interested to contribute to the public good. Implicitly most have assumed that these two approaches are complementary or at worst additive. But this need not be the case. Behavioral experiments ?nd that if reciprocity-minded subjects feel hostility towards free riders and enjoy in?icting harm on them, the incentives provided by the anticipated punishment support near e¡Ë cient levels of contributions to a public good. Cooperation may also be supported if altruistic individuals internalize the group bene?ts that their contributions produce. But the e¢´ects of these two supports for high levels of cooperation may be less than additive. Using a utility function embodying both reciprocity and altruism we show that unconditional altruism attenuates the punishment motive and thus may reduce the level of punishment in?icted on defectors, resulting in lower levels of contribution. Increases in altruism may also reduce the level of bene?ts from the public project net of contribution costs and punishment costs. The range over which altruism inhibits cooperation and reduces material payo¢´s is greater, the stronger is the reciprocity motive among group members.
