Endogenous Preferences and Private Provision of Public Goods: a ‘Double Critical Mass’ Model Angelo Antoci ∗ Pier Luigi Sacco † Luca Zarri ‡ October 5, 2004 Abstract In this paper we set up an evolutionary game-theoretic model aimed at addressing the issue of local public good provision via direct commit- ment of voluntary forces (namely, private donors and nonprofit providers) only. Two classes of agents are assumed to strategically interact within a ‘double critical mass’ model, where the provision and maintenance, on voluntary bases, of a public-type good is concerned. Uncertainty as to equilibrium outcomes emerges as within both categories a positive pro- portion of agents faces the temptation to opportunistically free ride on others’ efforts. Further, private donors and nonprofit providers’ payoff functions are interdependent, in the sense that (a) potential donors de- cide to be actual donors only insofar as a ‘large enough’ proportion of nonprofit organizations provides a high effort level, otherwise they act as free riders; (b) nonprofit organizations, in turn, prefer to exert a high productive effort only insofar as a ‘large enough’ proportion of poten- tial donors acts as actual donors, otherwise they exert a low effort level. Through this analytical framework, we are able to focus on the critical factors affecting the dynamic outcome of such interaction: under certain conditions, in a medium-long run perspective, even in contexts where, ini- tially, either a large proportion of agents behaves as free riders or a large proportion of nonprofit organizations exerts a low effort level, the local public good may be provided. 1 Introduction As far as private provision of collective goods is concerned, most part of the the- oretical models dealing with such issue tend to explain it by exclusively focusing on the features of the demand side, namely individual donors. 1 The basic goal of our model is to take a step further, at both methodological and substantive ∗ University of Sassari (Email:angelo.antoci@virgilio.it) † IUAV, Venice (Email: sacco@iuav.it) ‡ University of Verona and University of Bologna (Email: luca.zarri@univr.it) 1 It is worth specifying that it may sound puzzling to consider individual contributors to nonprofit organizations as part of the ‘demand side’. The point is that, though they may not be 1