The economic dimension of the innovation phenomenon is no longer sufficient to explain often conflicting processes of social relation changes caused by the intervention of actors to meet the needs of a social nature. This gap has prompted alternative perspectives to address social innovations. As a contribution to the knowledge on how social innovation is legitimized, the objective of this case study is to understand, in light of Pragmatic Sociology and studies on rationality, the legitimation process of social innovation related to the "critical case" of the Volunteer Fire Corps of Joinville. This thesis, result of convergence among multiple theory streams, lies in an attempt to recognize the plurality complexity of the main power (worth) sources present in social contexts, situated in the midst of the criticism surrounding the social innovation phenomenon. Finally, further comments on entrepreneurship and innovation were presented in both economic and social dimensions.